How To Parallel Port.

How To Parallel Port.

Since its launch, the parallel port - also known as Centronics port - has been synonymous with printer port.
Although a serial port can also be used to send data from PC to some printer models, the door
Parallel is faster. A serial port sends data one bit at a time over a single wire. A parallel port can
send multiple data bits through eight parallel wires simultaneously as soldiers marching side by side. The same
time a serial connection sends a single bit, a parallel port is able to send a byte integer. Or, another
approach, while a serial connection sends the letter A, a parallel port can send the word pin.

A parallel connection is a limitation. The voltages on all its lines to generate crosstalk, a phenomenon which causes
tension fade up from one line to another, the same thing that happens when you hear a third person interfering
their telephone conversation. The larger the cable the greater the interference. The maximum limit for a parallel cable is 10 feet
(Approximately 3m).

Some older printers and plotters used the serial ports as a means of communication. But today, as
vector fonts and graphics features that have become common in most printed documents, there is need for greater
amount of data is sent to the printer, making the parallel port the only option available. In addition, the doors
parallel are used to transport files between two PCs, and the popularity of laptops - many
often are deficient in terms of expansion slots - created a market for peripherals such as disk drives and
sound generators that use parallel ports.

Source: Evolution of Computers

Serial Port.

Serial Port.

The example presented here shows a serial port - connected to a modem - which follows the standard RS-232.

1 - Pins 1 and 5 of the computer port to connect respectively to pins 8 and 7 from the modem port. Pins 1 and 8
share the same ground connection. 5:07 The pins allow the PC to detect a signal from the telephone line.

2 - Pin 6 - the same on both sides - it sends a signal indicating that data is ready to be sent.

3 - Pin 4 PC connects to pin 20 of the modem. It signals that the PC is ready to receive data.

4 - Pin 7 PC connects to pin 4 of the modem. He makes a request to send data.

5 - 8 pin PC sends a signal to pin 5 of the modem when the PC is ready to receive data.

6 - Pin 2 PC sends data to the modem pin 3. Only one bit - here exemplified as a hub for bit blue
1 and a red ball in bit 0 - the cable can pass at a time. The fact that the data is sent serially, gives
name to such connection.

7 - Pin 3 PC receives data from the modem pin 2. Again, the bits can move by only one cable at a time.

8 - 9 pin PC conccta up to pin 22 of the modem to detect the phone ringing.

Source: Evolution of Computers

How To Serial Port.

How To Serial Port.

Without the serial and parallel ports of your computer, much of the work performed by the PC would never be seen by anyone
the person who was sitting in front of him. The serial port is the type workhorse among components
computer. Its concept is simple: one line for sending data, other for receiving and a few more to
regulate how data is being sent by the other two lines. Due to its simplicity, the serial port has been
used for the PC to communicate with almost every device imaginable - from the known modems and printers
until plotters and alarm systems.

The most common use is for the serial mouse or modem. The reason is that the serial port is not a very efficient
for data transfer. She can only send data serially - one bit of data at a time, like soldiers marching
in queue. However, this inefficiency for data transfer is acceptable to use the mouse, which transmits a quantity
so little data that the speed is not really crucial, and perfect with respect to modems because with technology
current telephone lines can not carry more than one signal at a time.

The serial port is commonly known as RS-232 port. This is a specification of the Electronic Industries
(Electronics Industries Association) for a pattern of how the connectors are used on a serial port. The problem is
this pattern is not always taken into consideration for peripheral manufacturers and even by the manufacturers of
computers. The fact of connectors, either 9 pins or 25 pins, are used as serial ports shows that even
we have a long way to go before establishing exactly what is an RS-232.

Source: Evolution of Computers

Liquid Crystal Display.

Liquid Crystal Display.

1 - The light - emanating from a fluorescent panel located behind the screen of a laptop - it spreads in waves
vibrate in all directions.

2 - a polarizing filter located in front of the light panel, only allows the passage of light waves that are
vibrating more or less horizontally. The fact that a polarizing filter is not completely accurate makes the monitor
create different shades.

3 - In a layer of liquid crystal cells, the internal video card laptop computer applies a variable load
electric current in some cells and no load on the other. In cells with current, larger molecules in
rod shaped material comprising the liquid crystal reacts to the load, forming a helix. The more potent is the
load, the molecules form spirals. With a very strong charge, the molecules from one end of the cell is viewed
90 degrees with respect to the orientation of the molecules of another end of the cell.

4 - The polarized light that enters the cells behind is twisted through the spiral molecules. In cells where it was
a total load applied to the vibrating polarized light emerges with an angle of 90 degrees to its original alignment.
The light that passes through the cells which have no charge emerges unchanged. Cells that received rotate partial load
light at an angle between 0 and 90 degrees, depending on the amount of charge received.

5 - the light emerging from each liquid crystal cell passes through one of the three color filters - red
blue or green - arranged close to each other.

6 - colored light beams pass through a second filter polarizer aligned to allow passage of only
Light waves that vibrate are more or less vertically. The light that passed through the liquid crystal which was applied
total electrical load is perfectly oriented to pass through the second filter.

7 - As the filter is not completely accurate, some of the light waves that passed through the cell with partial load - and that
consequently, were partially torddas - pass through the filter while the others are blocked.

8 - In this stage, the light was not twisted at all when passed through the liquid crystal is completely blocked.
In the example shown here, were issued 100 percent red beam; spent 50 percent of light green and light blue
was completely blocked. The result appears to the human eye as a single point of light brown dimmed.

Note - 0 example presented here shows only one form of such liquid crystals and polarizers manipulates
Light. Some liquid crystal panels using two polarizers with the same alignment, so that the load applied to the
Liquid crystal cell resulting in a light blocked by twisting two methods are also used to carry the
liquid crystal cells. The passive matrix displays use relatively few electrodes arranged on slides in
liquid crystal layer and let the time for the cells to manage receive the correct load. The loads on the monitors
active matrix weaken rapidly, creating faded colors. The active matrix displays, such as the example
shown here have individual transistors for each of the cells, such load transistors provide a more
precise and powerful, giving more vivid colors. But the monitors have an active matrix production more expensive because about 80
percent of them are usually discarded due to malfunction of the transistors.

Source: Evolution of Computers

VGA Monitor Table.

VGA Monitor Table.

1 - The digital signals from the operational environment or program is received by the VGA card (sometimes built into the motherboard
PC). The board passes the signals through a circuit known as a digital-analog converter (DAC). Typically, the
circuit is in particular a chip that has actually three DACs - one for each of the three primary colors
used by a monitor: red, blue and green.

2 - The DAC circuitry compares the digital values ​​sent by the PC with a table containing the verificagäo degrees
voltage (voltage) that match the three primary colors needed to create the color of a single pixel. The table contains
values ​​for 262,144 possible colors, of which 256 can be armazendas in memory of the VGA card. (Super VGA monitors,
which have more memory may manage greater number of colors and higher resolutions, the more pixels).

3 - The board sends the signal electrons of three triggers, located at the rear of the cathode ray tube (CRT)
monitor. Each electron trigger sends an electron beam, each beam goes to one of the three primary colors. The
intensity of each beam is controlled by the signals of the plate.

4 - The board also sends signals to the mechanism that is in the neck of the CRT that focuses and directs the electron beam.
Part of the mechanism, a deflection coil (magnetic deflection yoke), uses magnetic fields to deflect the direction of
electron beams. The signals sent to the deflection coil help set the display resolution - the number of pixels
vertical and horizontal - and vertical scan rate (refresh rate) Monitor, which is the frequency with which the image of
screen will be redrawn.

5 - beams pass through the holes of a flat metal known as shadow mask. The purpose
this mask is to keep the electron beams correctly aligned in relation to their targets within the screen of the tube. The dot
pitch of the CRT is the measure of how close the orifices are each other, the closer they are, the smaller the dot pitch.
This, in turn, generates a more accurate picture. The holes in the majority of shadow masks are arranged
triangularly, with the important exception of the Sony Trinitron tube, used by several manufacturers of monitors.
The holes in Trinitron are arranged in parallel slots.

6 - The electrons hit the phosphors coating the inside of the screen. (Matches are materials that glow when hit
by electrons). fóstro Three different materials are used - one for red, one for blue and one for
green. The stronger the electron beam reaches the match, the more light it will emit. If each point red, green and
blue composition is reached with equal intensity by the electron beam, the result will be a point of white light.
To create different colors, the intensity of each beam is varied. After a spot beam leaves a match,
This still continues to shine for a time, a phenomenon called persistence. For the image to remain
stable matches must be reactivated by repeated scans of electron beams.

7 - Once the beams perform a horizontal sweep across the screen, the electron beam is turned off while the
triggers electron beams deviate to the left end of the screen, at the point just below the scan line
earlier. This process is known as horizontal scan tracking.

8 - deflection coil continuously changes the angles of curvature of electron beams so that they sweep across
the surface of the screen, from top left to bottom right edge. This full scan of
screen is known as a field. After completing a field, the beams return to the upper left corner to
start a new field. The screen is usually reconstructed or redesigned, about 60 times per second.

9 - Some video cards sweep line but not in the online field, a process known as entanglement. Interlacing
allows the card to generate higher resolution - ie, more sweeping lines - with cheaper components. However, the decrease in
intensity of matches between each pass is more visible, making the screen flicker (flicker).

Source: Evolution of Computers

How To Monitor.

How To Monitor.

A few years ago, color monitors for personal computers were considered a luxury - most appropriate for games
than for the job itself. Most programs was based on text mode and text displayed on color monitors
was of poor quality and difficult to read. Even for graphics applications, monitors color graphics (CGA),
who were the first to appear for DOS based computers, had serious difficulties in showing only
four colors of the 16 colors available in its highest resolution - a resolution full of zigzags in place
mild curves and lines defined.

Today, the reality is another. Not only the color is considered acceptable for the work computer, as I became
required in this field due to the use of environments such as Windows or OS / 2, requiring more of the graphics. The
Programs currently used to color not only to make them more attractive, but to add greater amounts of
Information.

Color monitors are far more recent colors and resolutions arid models of the past decade. In ten of the
four colors now have a palette of at least 256 colors and some even thousands of colors. In place of the old
CGA resolution of 200 lines by 640 columns of pixels, most modern monitors have a resolution of 768 lines per 1,024
columns of pixels, effortlessly. (A pixel, short for picture element, or component screen, is the smallest unit
logic that can be used to construct an image inch screen. A single pixel is normally formed by grouping
several points of light (dot). The smaller the dots used to create a pixel, the better the resolution of the monitor.)

The secret of the best monitors currently found is the combination of VGA video adapter (Variable Graphics Array)
with versatile monitors that can operate with a variety of signals from the video card. The oldest video cards
used exclusively digital information that informed it was a pixel on or off, making it difficult to distinguish
between shades of color. The VGA utilizes an analog signal converts the digital information into different levels
voltage varying the intensity of a pixel. The process requires less memory and is more versatile. Super VGA monitors
use a set of special chips and more memory to further increase the number of colors and resolution.

In the coming years, some type of VGA monitor will become standard. We'll look at two types of VGA monitors colorful -
the desktop display and liquid crystal display of the notebook computers.

Source: Evolution of Computers

the Keyboard Scan Codes.

the Keyboard Scan Codes.

1 - Regardless of the type of key used, the act of pressing it will cause a change in current flow through the
circuits associated with the key.

2 - A microprocessor such as the Intel 8048 within the keyboard constantly scans circuits leading to the key.
It detects the increase and decrease of power button being pressed. When it detects an increase or decrease
the stream, the processor can say so much whether the key was pressed or released. Each key has a particular
A set of codes, even for users that they appear identical. The processor may, for example, to distinguish between
Shift left and right. To distinguish between a real signal and abnormal fluctuations in the current scan
is repeated hundreds of times per second. Only the signals sensed by two or more scans have significance for the
processor.

3 - Depending on which key circuit bears the signal to the microprocessor, the processor generates a number, known as
scan code. There are two scan codes for each key, one for when it is pressed and another when it is
released. The processor stores this number in the buffer memory of the keyboard itself and loads it into a connection port for
that can be read by the computer's BIOS. Then, the processor sends an interrupt signal through cable
keyboard, stating that there is a code scan waiting for him. An interrupt requests that the processor set aside
whatever you're doing and turn your attention to the service being requested.

4 - The BIOS reads the scan code from the keyboard port and sends a signal to the keyboard, informing him that the code can
be cleared from memory.

5 - If the scan code is on a key obtained from or Shift keys to a considered
special or two states - Ctrl, Alt, Num Lock, Caps Lock, Scroll Lock and Insert - BIOS change two bytes in an area
special memory to record which keys were pressed.

6 - For all other keys, the BIOS checks these bytes to determine if a key was pressed with Shift or
special. Depending on what you find, the BIOS translates the scan code to ASCII code, used by the PC, which
represents a character or a special code for function key or key cursor movement. The characters
lowercase and uppercase have different ASCII codes. In both cases, the BIOS sets an ASCII code or key
special in its own memory, which will be sought by the operating system or the program so that the operation
is being carried out has finished.

Source: Evolution of Computers

Keypad - keys physical contact.

Keypad - keys physical contact.

1 - In a physical keyboard touch the keys pressionamcnto you slide a capsule of foam rubber.

2 - The capsule press a blade of plastic, located at its lower end, which in turn has an area
Metal connected to the rest of the printed circuit board of the keyboard. The metal surface comes into contact with a
similar surface on another plastic sheet, allowing current to pass through the printed circuit connected
each of the cushions.

3 - When the key is released, the capsule back to its original shape, releasing pressure on the plastic blade. The plastic
also returns to its original position, breaking the circuit and cutting the chain.

Source: Evolution of Computers

Keyboard - capacitive keys.

Keyboard - capacitive keys.

1 - in a capacitive keyboard, pressing the button compresses a spring that causes a plunger plastic and metal
move closer to the two pads fixed on a surface covered by a combination of tin, nickel and copper.
The pads are connected to the printed circuit board of the keyboard. Although the two metal areas never touch each other, they
act like a capacitor therewith maintaining a positive charge and the other a negative equal. The lowering spring
some keyboards is designed in such a way that generates a mechanical click.

2 - The plunger of metal passing between the pads reduces the load contained therein. The difference causes a small load,
but noticeable current flowing through the circuit connected to the pads.

3 - When the key is released, the spring expands, turning the key to its original height by moving the plunger out of
metal pads and causing it to flow - flowing through the circuit pads to which leads - to return to its
original level.

Source: Evolution of Computers

How the Keyboard Works.

How the Keyboard Works.

You have direct contact with the keyboard than with any other component of your PC. You can go years without the
see less - much less play - the processor or hard drive of your PC, but most people pay much
more attention than these components in one part of the computer that does not define the proper functioning of the computer, but the
quality of work performed on it.

A poorly designed keypad locks productivity and can even cause health problems. A well-designed keyboard
is that you even forget it exists; thoughts seem to flow freely to the screen of your computer without you
aware of what your fingers are doing.

Despite the importance of the keyboard, most manufacturers - and many users - pay little attention to this part. Today
days, some keyboards have built-in trackball or other pointing device. Some have drawings
different, the designers believe alleviate repetitive motion syndrome. The few changes that have emerged -
keyboard with concave keys equidistant fingers or keyboards where you can work with only one hand - not
caught.

Regardless of the manufacturers do not have the imagination or the computer users are not interested, the
basic operation of a keyboard not changed significantly since the first appearance of the early IBM PC
80. Although the provision of all keys except the alphanumeric is at the top - especially in
keyboards of notebooks - the only practical difference in how keyboards work lies in the mechanism that converts
movement of a keystroke on a signal sent to the computer. We'll see how these two mechanisms: contact
physical and capacitive. Except for this difference, the movement of the signal from the keyboard to the PC is a technology
tested by time.

Source: Evolution of Computers

​​Data percorendo the bus.

​​Data percorendo the bus.

1 - The signal processor or other components undergo several parallel lines of the circuit. The number of lines
depends on the type of architecture used by the bus. The simplest - the 8-bit bus used in the original IBM PC
- Uses sixty-two lines to connect expansion boards. Any signal sent to a board is received by
all others.

2 - Eight lines to transmit electricity boards. Different lines have different voltages.

3 - Eight of the thirty-two lines are used to transmit any data, whether the data is intended
the memory chips, the monitor or the disk controller.

4 - Twenty lines carry information that determines the address where the data should be taken. Each expansion card
uses a unique address and specific - all available from the first megabyte of memory - that can be addressed
by the operating system.

5 - The remaining lines are used to transmit control signals to certain specific commands such as
read and write commands to the memory device and for each input / output.

6 - Each board bus constantly looking for signs in the appropriate command lines. When a sign appears
the command line recording, for example, all input / output acknowledge the command, and circuitry
Memory not.

7 - The boards I / O alerted by the write command, the lines are aware dc address. If the specified address
these lines is not used by the card, it will ignore the signals sent by the data lines.

8 - If the signals from the address lines match with the address used by the card, accepts this data sent
by lines, using them to supplement the recording program.

Note - Recently, a new form of communication with peripherals gained popularity. This is the place bus or
local bus, which overcomes the speed limitation imposed by the other bus designs. Original bus 0
was designed to operate at 8 MHz, about twice as fast as the processor of the IBM 8088 PC. While
Processor speed increased to 10 MHz, 25 MHz, 33 MHz, 50 MHz or more, the bus remained at 8 MHz with the
Local bus design, it has become possible to transmit 32 bits of data in the local speed of the processor of the PC.
Generally, a PC with local bus architecture limits this to one or two slots, used by video cards or
disk controllers, where speed is necessary. The slower expansion slots are used for communication
with the serial and parallel ports and the keyboard, where speed is not as important a factor.

Source: Evolution of Computers

Differences between the buses.

Differences between the buses.

8-bit bus - The data is transmitted to the expansion slots and the other components of the bus only
8 by parallel lines of data.

Or ISA bus of 16 bits - The data are transmitted through 8 or 16 lines of data, depending on the type plate
used in the expansion slot.

MCA or EISA bus - The data is transmitted to the plates designed specifically to work with buses
Bit 32 through 32 data lines. MCA expansion slots do not accept cards of 8 or 16 bits.

Adaptability EISA - The design of the expansion slots EISA allows plates 8 or 16 bits are fit enough
to make contact with the line 16 connectors that manage the data based on the EISA bus. But the plates designed
specifically for the standard EISA can fit deeper and align its connectors to the 32 special fittings slot
that manage data based on standard EISA.

Source: Evolution of Computers

How the Bus Works.

How the Bus Works.

One of the most brilliant ideas behind the personal computer is the expansion slot - connectors to insert new
circuit boards that connect to the rest of the PC via circuitry known as bus, or bus. The
expansion slots for transforming a personal computer so that it can pass the tasks ever
imagined by the designers of the machine. Inserting the right plate - usually called adapter plate, or
expansion - it is possible to increase the resolution and number of colors used by the video, turn your PC into a machine
that records and plays music, make it work with disk drives, printers, backup tapes and as host
peripherals that did not even exist when you bought the computer. Bus circuits are used also for
communicating with some peripherals - such as keyboard - not connected to an expansion board.

The advantages of the expansion bus are so obvious that one might think that all computers have this feature. In
Indeed, before the advent of the IBM PC, many computers had their fixed components, ie, could not be
changed. The designers, on their own, decided to produce the artwork, not imagining that anyone would want
add something to it.

When IBM introduced the first PC, she was smart enough to realize that they should create a computer
accept and expansions should also disclose all the necessary technical information to other companies
could develop expansion boards for the IBM PC. The result was the emergence of a slew of new
components that, since then, continue to push the boundaries of what can be done with a personal computer.

The bus became, next to the microprocessor, the most critical factor for performance and differentiation between
classes of computers. Trends to be adopted by the new buses will determine the future of the PC itself.

Source: Evolution of Computers

Device inlet and outlet.

Device inlet and outlet.

All the wonderful tasks that a personal computer is capable of running would not have any meaning if he had not
a way to communicate with the outside world. Early personal computers such as the Altair, used a method
communication so primitive that is admirable how the pioneers of computing had imagination to create a contraption
that could offer any practical use in the real world. Instructions and program data were introduced in
computer through electrical switches - and not the type miniaturized transistors, but the size of a thumb. The
computing results were shown in a pattern of seemingly random small lighted lamps on a panel.

Nowadays, the forms of communication that we use with devices that include PCs even more pioneers
visionaries of personal computing be able to imagine. The keyboard and cathode ray tube (CRTs) are so common that
is hard to think of a PC without them. There is also the modem, scanner and mouse that help us to get information and
instructions from the outside world. In addition to traditional CRT there is a series Monitors advanced as the monitor SuperVGA
active-matrix color, and printers capable of far better things to offer than just print letters rudimentary.
With this, the personal computer became part of our real world, to the point of becoming something that is to be treated more like
human - someone who listens and responds - and less like a pile of microchips and electronic components.

In summary, most of external devices to the microprocessor - in other words, most of PC - constitutes
device input or output. Each act of reading or writing data to a disk drive or memory
uses the BIOS service (acronym for Basic Input / Output System, or the basic input / output) of the computer.
Still, we usually associate only the input and output devices such as the keyboard, monitor and mouse, of which
rely on to do our work. The restricted vision we have of the importance of input and output devices is
understandable, though without them even the most powerful PC in the world no more than a clumsy tool for
interest and a curiosity for others.

Source: Evolution of Computers

Vector Interlaced Disk Drive

Vector Interlaced Disk Drive.

1 - When a file is to be recorded on Interlaced vector, for example, three units, it is divided into two
parts so that each part is recorded on a separate drive. The vector interlaced requires at least three units
disk. Typically, vector writes the data to all units but one that is used for error checking.

2 - The program of the Company or vector performs a Boolean operation XOR the data recorded on the disk drives and
then writes the result of this operation, called a parity bit, the remaining unit. An XOR operation results in
bit 0 whenever two equal bits are compared, and 1 bit whenever two different bits are compared. Eg
applying XOR in binary numbers 1100 and 1010 arrives at the 0110 parity. If more than three units in the vector, the
two first XOR make the comparison and the result will be the third, and so on until the final result becomes
the last unit. This operation invalidates much of the performance achieved in the first stage, with simultaneous recording
the different parts of the file.

3 - When a file is read into a vector interlaced disk drives, the Company typically seeks each
in different parts of the file on disk drives that have been recorded.

4 - In the event of damage to one part of a file or disk drives, the controller performs the opposite
an XOR operation. Comparing the undamaged bits with parity bits, the controller can infer that the
missing bits are 0s or 1s. The information can also be used to repair data lost due to physical defect
in the media.

Source: Evolution of Computers

Vectors Mirrored Disk Drive.

Vectors Mirrored Disk Drive.

1 - When a file is written in a vector mirrored disk drives, the controller sends both copies
File identical to each unit forming the assembly. Mirroring can be done from two
disk drives.

2 - When a vector file mirrored disk is to be read, the controller simultaneously search
alternating clusters of this file in each of the units, putting them together (in ordered sequence) to be
sent to the PC. This process makes reading faster, but the speed depends on the number of mirrored drives in the array.
If there are only two, the reading time is reduced by half, approximately, three mirrored drives, the time may
drop by about one third in relation to a unit.

3 - In case of a read error - caused by defect in the surface of one of the units or damage occurred in
one - the parent simply reads the version of the file intact on the drive that does not display any defects.

4 - If the read error is caused by a defect in the media, the controller automatically reads data from a copy of the
file on another drive, burning it to a new area and no defect in the unit in which the problem occurred.

Source: Evolution of Computers

How does it work Vector Disk Drive.

How does it work Vector Disk Drive.

The array of disk drives is based on the theory that if a hard drive is already a good thing, two units
disk is twice as good and five units quintuplicam this positive quality. Using multiple units of
hard drive configured for the operating system to function as if there were only one, the personal computer can
acquire great speed when reading data or greater protection against the loss of these. In fact, one can achieve
it economically.

The most common type of vector units is called RAID (an acronym for Redundant Array of Inexpensive Drives) or vector
redundant units cheap. Models with greater capacity and speed, the cost of hard drives has increased. But
with RAID, you can use multiple disk drives cheaper and have a total cost less than a model of high
performance, uniting similar performance and greater data security.

RAIDs using a combination of mirroring and / or entanglement, both methods provide great protection against
data loss. Mirroring, in which a disc is direct copy of the other, produces a great increase in performance, but it has
high cost. The entanglement, in which the files are spread across multiple disks and protected against data loss
another disk, is used when data protection is required and performance has priority.

Typically, the vectors of disk drives in PCs are rare independent because, despite the tactic being used
inexpensive disks, the vector as a whole is still expensive compared to the cost of most of the individual components
the PC. Vectors are more common in PCs that function as servers LANs.

Source: Evolution of Computers

DAT Tape Drive to Backup.

DAT Tape Drive to Backup.

1 - When you give a command backup, the program checks the file allocation table of the hard disk to
find those that will be copied. Then the program copies the data file to file to the buffer unit
digital audio tape (DAT), which generally behaves 512KB to 1MB of data. As in the case of QIC tape drive, the
DAT drive applies an algorithm to the data to create a code error correction that is added to the data contained
in the buffer.

2 - It is the unique design of the head read / write units DAT which lets you copy large amounts of
data in a tiny cartridge of similar size to a matchbox. The mechanism is a rotating cylinder with
four heads separated by 90 degrees. Two of them, the recording heads A and B, write the data to be
copying, and the other two reading verify the data. The cylinder tilts slightly so you can rotate according
the angle of the tape. It rotates 2,000 times per minute while the tape passes in front of the cylinder in the opposite direction
rotating at a speed of 1/3 inch per second.

3 - While The recording head maintains contact with the tape are recorded approximately 128KB of data and correcting codes
Error buffer unit for a track of the tape. As the cylinder is inclined to one end of the head is
tape at the beginning of the read head and moves diagonally across the tape to find the other end. This raises
a narrow diagonal eight times longer than the width of the tape.

4 - The read head reads the data back and checks the track, bit by bit, comparing them with the data still
are in the buffer. If the tape data are correct, are removed from the buffer and more data is read from the hard drive.
If the data contained in the present track errors will be recorded again in the next passage.

5 - The recording head B passes through the tape and writes data on a track with 40 degree angle relative to the track,
performing a type of intersection that overlaps the track A. The overlapping data store for more information
inch tape, and are not confused later because the magnetic bits written by the two heads have
different polarity, and the other two heads only read data tracks correctly aligned.

6 - reading head B recording and B satisfy the same process steps alternating with the other heads A until
all data has been copied. Then, the unit rewinds the tape and writes the directory of the files stored
a special part in the beginning of the tape or a hard disk file.

Note - To restore files from a DAT drive, the program reads the directory, move the tape to the starting position
where are the files you want and copy them to the hard drive.

Source: Evolution of Computers

Backup Drive Cartridge for 1/4 inch (QIC).

Backup Drive Cartridge for 1/4 inch (QIC).

1 - When you send a command to be made a backup, or backup, the drive QIC (acronym
Quarter-Inch Cartridge), the program reads the file allocation table (FAT) hard drive to locate files
to be copied. The program stores the directory information in a buffer in 32KB RAM PC. Then, copy the
files to the same buffer. Each file is given a header (header) that identifies and reports its position in the tree
the hard disk directory.

2 - If the tape drive controller has chips that manage error correction, the program backup
unloads the entire buffer in the RAM buffer controller itself, so that the chips add-correcting codes
error (CE). If the parent does not have built-in error correction, the program executes the code as the standard EC
bits 0 and 1 of the files, attach them at the end of the data in the RAM buffer and copies the entire contents of the buffer RAM for
buffer controller. When the data have already been transferred to the controller, the buffer RAM will be free
to receive the next data block from disk.

3 - The tape drive controller sends signals to the mechanism of the tape start moving. QIC drives
depend on the cartridge to keep the tape taut. When the capstan (or capstan) unit rotates the drum cartridge,
an elastic strap that surrounds the reels stretches them slightly to attach the ribbon, allowing the reel started
movement balancing tensile strength with resistance reel containing the tape. Thus, the tape is pressed
against the head of the unit steadily reducing errors read and write.

4 - The controller sends a data stream to the recording head unit. Many tape drives have a head
with three parts of type read-write while. Two read heads flank the central recording head which transfers
data for the magnetic coating of the tape. Depending on the movement of the tape, one of read heads which reads data
just been recorded by the recording head to verify that the data contained on the tape are the same as that
recording head sent to tape. If the scan does not find error, the buffer is emptied and the parent
unit switches to the next section of disk data. However, if any errors are found, the data is rewritten in
next section of the tape.

5 - The format of a QIC tape contains basically 20-32 parallel tracks. When the tape reaches one of the moving
roll ends, reverses the direction and flow of data back to the next track out. Each track is divided
in blocks of 512 or 1,024 bytes, with each segment contains 32 blocks. Among the blocks contained in a segment eight
contain error correction codes. Furthermore, at the end of each block, the unit runs a test or cyclic redundancy
CRC (Cyclic Redundancy Check acronym) to better ensure the correctness, adding it to the block. Most
programs backup reserve space at the trailhead 0 or a separate track for a directory
security files.

6 - As the end of the tape approaches the head unit, the orifices placed on the tape so that the signal
unit reverse the motion and change the active area of ​​recording up or down, searching for the next track
continue the recording process. When all the data have already been recorded, the program updates the backup
the directory of the tape according to the trails and locations of the files that were copied.

Note - To restore a file, the unit uses the directory of the tape to locate the file and read it in its buffer.
The controller reserves a CRC code for each block, comparing it with the CRC code recorded at the end block. If
difference, the error correction routines can generally fix the data using the codes contained in each EC
data block. Once the driver's buffer is full, the data is written to the hard drive in the directory
appropriate.

Source: Evolution of Computers

How To Tape Backup Unit.

How To Tape Backup Unit.

Make a backup of your hard drive in a tape drive is comparable to one of those advice given by their
mother when you were a child: Take an umbrella that day is cloudy and put a coat. Okay, his mother had
reason from time to time - it might rain and you get wet, but that was not such a horrible thing. And if the table
allocation (FAT) file from your hard drive stay cluttered making you lose half of your files? There are some
years while it is copied important data files on floppy disks, recover some megabytes of programs was not
so serious.

Today, however, the implications of a small accident on the hard disk acquired astronomical proportions. We are not
talking more disk drives with a few tens of megabytes in file, but hundreds. A simple program that runs on
Windows can contain about 20 megabytes of files. And with such a complex environment such as Windows, no program
there alone. Each program for Windows installed will modify at least one of the files. INI Windows. Furthermore,
many tricks you may have done on your system - from hidden parameters for a line driver device
that manages memory in CONFIG.SYS to improve the color scheme of Windows - things you no longer remember.

At the same time growing the need to back up the hard drive units with 200 megabytes or
become more abhorrent the idea of ​​verbatim copies. This situation has given rise to a new, cheaper and more appropriate
generation of backup tapes. Priced around $ 500, these tapes are feasible even for those who have computers at home.
The advantage of being able to copy a gigabyte or more on a single tape further simplifies use even for hard
Larger hard.

Here's how they work internally both types of tape backup best known: the cartridge a quarter inch
(QIC) and digital audio tape (DAT).

Source: Evolution of Computers

Bernoulli Drive.

Bernoulli Drive.

Spindle Read / write head.

1 - When the flexible material that comprises the internal disk cartridge Bernoulli is at rest, the hard stoops
naturally, away from the head read / write drive.

2 - When the drive shaft (spindle) starts to spin the disk, the movement pushes the air into the opening in the
flat surface to the upper disc. The air beneath the disc, being practically stable, has
greater pressure against the bottom of the disk that the pressure exerted by moving air above it. This difference in pressure
makes the hard climb towards the surface. The same effect on the Bernoulli increases when the head
read / write protruding through the surface, causing the disc even closer it.

3 - The disc does not touch the head because the stationary flat surface creates an air barrier between the head and the disk. The
opposing forces that promote the lifting and air barrier causes the disk is stabilized at 10 millionths
inch head read / write closer than the distance between a conventional hard disk and a head
read / write.

4 - If there is any possibility of any damage to the hard drive - such as lack of energy or strong vibration
unit - the unit disc Bernoulli down a bit, moving a safer distance in relation to the head
read / write, thus reducing the chances of the disc touching the head and damage the surface layer of magnetic film
in which data is stored.

Source: Evolution of Computers

How the Unit Works Bernoulli.

How the Unit Works Bernoulli.

In the eighteenth century, the Swiss mathematician Daniel Bernoulli was the first person to describe a special phenomenon of dynamic
fluids involving water or moving air. The principle is the same Bernoulli noted that makes a plane
lift off the ground.

Bernoulli noticed that the faster the air moves, the lower the pressure exerted by the object that is flying. The wing
a plane is curved at the top so that air about her having to travel faster than the air that moves below
her. But as the air currents passing through the two parts of the wing must follow their respective directions, the same
time, the upper air must move faster. When the air presses the bottom
wing with more force than the air above the wing, the plane takes off. You can demonstrate this principle even blowing part
top strip of paper.

The Bernoulli principle inspired an unusual storage device, created by Iomega Corporation in the early
80. He was different because he had the same capacity of hard drives at the time, but the disc could be removed,
just like a floppy disk. The Bernoulli Box, as it is called, has unlimited capacity mass storage, and more
appropriate that the floppy disk drives.

Since then competitors have developed various types of removable hard drives. But few devices beyond
Bernoulli Box offer protection against damage the drive head.

Source: Evolution of Computers

Reading Data from Disk Magneto-Optical.

Reading Data from Disk Magneto-Optical.

Sensor Aluminum Alloy Plastic Plastic.

1 - A laser beam is focused on the weaker tracks with the data that was previously recorded by a laser beam
more intense.
2 - The laser beam is reflected by the surface existing in the aluminum alloy layer. When the beam passes through the league,
polarizing the aligned crystals, allowing to pass only light rays that are vibrating in a certain direction.
3 - The sensor reads the reflected light and determines the direction of its polarization. The alignment of the crystals in bits 1 polarizes
light in one direction, while the alignment of crystals in bits 0 polarized in the other direction.

Source: Evolution of Computers

Writing Data in Magneto-Optical Disk.

Writing Data in Magneto-Optical Disk.

1 - An intense laser beam focused on the disc surface, consisting of a crystalline metal alloy with a few atoms
thick. The alloy, which polarizes light, overlying a substrate of aluminum. Both alloy as the substrate lie between two
plastic layers.

Laser Plastic Aluminum Alloy Plastic.
2 - The laser beam heats a tiny spot grade alloy than the critical temperature known as the Curie point.
At the Curie point - which varies according to the material - the alloy crystal (alloy) are released in sufficient quantity
that can be attracted by the magnetic field.

3 - A recording head, similar to conventional disk drives, creates a magnetic field that aligns the crystals
league in one direction to represent the bit 1, and in another direction to represent the bit 0. The area affected by beam
laser is so small that it can store up to 500MB of data on a single side of the disc 5 1/4 inches.

Source: Evolution of Computers

How It Works, Magneto-Optical Unit.

How It Works, Magneto-Optical Unit.

Magnetic signals used by floppy disk drives and conventional hard disk recording data on tracks
microscopic. And even if used on a universal scale, are rudimentary. In contrast, a light beam produced by
laser can be reduced to a much smaller area than that achieved by the head read / write magnetic most sensitive.
Logically, if a laser beam can be used to read and write to disk, this means that more data can be
stored in the same space.

The first experiments to direct the laser beam as a device read / write resulted in products
WORM, acronym for Write Once, Read Many (write once, read many times). A WORM can actually store hundreds
megabytes of data on a single removable disk. The problem about him is that, after the data is written to
disk is no longer able to change them or delete them. An elaborate scheme to search for a new track enabled version
file that can be burned to disk escobrindo its original version. The scheme worked well, but was not the solution
ideal. Theoretically, it is possible to fill in a WORM disk with a 500MB file only 1KB. Currently, the units
WORM are useful only to keep track of transactions for audit unchanged.

A solution to the removable memory storage that allows data to be erased and altered emerged with
units magneto-optical (MO), which combines technology and the advantages of conventional magnetic units with the
CD-ROMs and WORM drives based on beams of light. The laser used in the MO drives allows data to be
compressed so that hundreds of megabytes of information are stored in a single disc that can be
transported - as a CD - from one machine to another. Just as in the magnetic units, it is possible
record, edit and delete data without the limitation of reading the CD-ROM and limitations of recording units
WORM. In addition, the disks do not have magnetic fields that may be affected by temperature. As the head
read / write unit MO far from the disc surface, there is less risk of damage. These two technologies
cause the magneto-optical disks are the ideal way to backup and transport of bulk data.

Source: Evolution of Computers

CD-ROM.

CD-ROM.

Land Disk Pit coil Focusing Objective Lens Prism Light-sensing diode Laser diode Sectors

1 - The motor constantly changes the rotational speed of a CD-ROM disk, no matter where the component named
detector relative to the disc radius. The portion immediately below the detector always moves at the same speed. (See note below.)

2 - The laser projects concentrated beams of light that pass followed by a coil focusing (focusing coil).

Note - Discs such as those used in magnetic hard disk drives have the data arranged in concentric circles
called tracks, which are divided into sectors in the radial direction. Through a scheme known as angular velocity
constant when the magnetic disk rotates at the same rate, i.e., the tracks near the outer edge of the disc move more
faster than the tracks near the center.
As the external sectors pass under the heads faster read / write, they must be physically larger to
can store the same amount of data that the domestic sectors. This format wastes a lot of space
on the disk, but maximizes the speed with which data is read.

Note - Commonly, CD-ROM uses a different scheme of magnetic disks to mark the areas of the disk that
the data are recorded. Instead of several tracks arranged in concentric circles, the CD-ROM data are,
in a single spiral track moves towards the center of the disc. The trail is also divided into sectors, each sector but
occupies the same physical size. Through the method known as constant linear velocity, the disk varies
continuously rotating the disc. Thus, when the switch moves to the center of the disc, it slows down. The
effect allows the CD contains more than one magnetic disk sectors and therefore, a larger amount of data. When the
detector moves toward the center of the disk, the velocity decreases, allowing time for the data to be read from disk.
A new type of CD called MultiSpin, far outweighs the CD.

3 - The laser beam penetrates the protective layer of transparent plastic material and has a reflective layer resembling an aluminum foil at the bottom of the disk.

4 - The surface of the reflective layer ALTEMA among the highest areas, or protrusions (pits), and the tiny low-lying areas or recesses (lands). These records form the two surfaces 1 and 0 used to store data.

5 - Upon finding a projection (pit) light is scattered but achieving a groove (land) returns directly to the detector by passing through a prism (prism) which deflects the laser beam to the photosensitive diode (light-sensing diode).

6 - Each pulse of light that hits the photosensitive diode generates a small potential difference (DDP) electric. DDPS These combine with a timer circuit to generate a stream of ls and Os that the computer can understand.

Source: Evolution of Computers

How Does CD-ROM.

How Does CD-ROM.

The CD-ROM uses small discs wrapped in plastic, similar to the compact discs of music in
which data are read by means of laser beams. As a music CD, the CD can store huge computer
because amounts of information using light to record data in a much more compact than the method used
by magnetic heads read / write of conventional disk drives. The computer CD also serves only
for reading, and you can not use it to record data.

The immense capacity and nature of the read-only CD-ROM, combined with the relatively low cost of
units to make them perfect way of storing large amounts of data that do not require updates
frequent. It is common to find CD-ROM image libraries (clip art), photographs, encyclopedias, works
Complete Shakespeare and even complete sets of reference works. The CD-ROM is also a component of
essential for multimedia systems, which use sound and video files, which are usually huge.
(An additional advantage of the multimedia features is that the CD-ROM are also able to play music CDs.)

Unlike CD turntables, the CD-ROM does not have many buttons and liquid crystal displays, except the button
used to insert and remove the disc and a single light that indicates when the disc is being read. The CD-ROM is
controlled by a program inside the PC that sends instructions to the circuit of the controller that is on the motherboard or
a separate card installed in an expansion slot. Together, the program and the circuit components manage high
technology. In comparison, this process makes the conventional disk drive device rudimentary.

Source: Evolution of Computers

Disk Cache.

Disk Cache.

1 - When you load a program from disk cache, the memory resident program reserves a portion of memory
conventional, expanded or extended, for their exclusive use. The amount used by the cache can range from a few
kilobytes to several megabytes of RAM. Generally, the more RAM uses a cache, the more effective. Some caches earmark
certain part of memory; others require all the available memory, but parts of the release memory when other programs
need it to perform their own tasks.

2 - The CPU under the command of the application, sends a command to the hard drive, requesting data. The cache intercepts
data request.

3 - The cache reads data from the disk satisfies the request and search more data, usually in clusters of adjacent unit.
The cache passes the requested data to the CPU, but keeps a copy of them with excess data sought in RAM reserved
above.

4 - In many instances, when the CPU is not actively engaged in processing instructions, the cache takes control to
read more data on the drive, which are also stored in RAM, usually the next sectors to files already read. Each
cache has an internal logic that makes discover which blocks are more likely to be requested later
by the application. The intelligence of this logic distinguishes the efficiency of a cache for another.

5 - Later, when the program requests more data, the cache again intercepts the request and checks whether the data
requested are already in RAM. If so, the cache provides directly to the CPU without having to access the disk. Otherwise,
caching repeat the previous procedure, seeking new data, fomecendo them to the CPU and also keeping them in RAM with the
clusters extras on the disc. When the RAM used by the cache is full, it releases the data that have been there longer
no use, replacing them with data collected during the most recent procedures disk access.

6 - When a program sends a command to write data to disk, some caches intercept the data, not the recording in
disk until the CPU is idle. This makes it faster computer operations because the attention of the CPU is not
divided between the disk and record other processing.

7 - If the file to be written to disk is still in the area controlled by the RAM cache, it writes to the disk only
clusters that have changed. Some caches also remain pending writes to minimize the movements of the heads
read / write drive.

Note - The disk cache controllers work similarly to programs cache, but do not use any
system memory, or to the logic that controls the cache not to store data in the cache. The controllers
cache usually offer better performance, but are more expensive than programs cache.

Source: Evolution of Computers

How does it Disk Cache.

How does it Disk Cache.

The slowest of any computer your drive. The units and the keyboard are the main items
personal computer that contain moving parts. The rest of the PC is simply to move the electrons from side to
other. But the mechanical parts moving in the real world, which takes into account the mass and inertia. No matter how
fast a hard drive can be mechanical parts seem sluggish compared to the other components that move
data at the speed of electricity.

There are ways to minimize this inherent slowness units. Some are faster than others. One is
make sure that the files are defragmented disk - ie, clusters that make up such files are
close to each other, and the read and write heads need not go all the physical space of the disk to unite
different parts of the file. Another way is to circumvent the problem by choosing a unit into RAM, which is part of
PC memory and is configured to cheat the PC, making it work as if it was a real unity.

However, despite these tricks, it is impossible to totally eliminate disk access. Reading programs and data files
the disc is essential for any self-respecting computer. The easiest and most efficient way to compensate for the slowness of
disk drives is to use a disk cache. Basically, a disk cache becomes faster computer operations,
maintaining data in RAM of your application that are most likely to be requested from the unit.

The concept behind the disk cache is similar to the cache RAM. But as the speed difference between
disk drive and any chip RAM is much greater than between a RAM chip fast and slow, causes the disk cache
results much more evident that cache RAM. There are several programs disk cache for sale, one of them came
MS-DOS. Some are better than others, but even the one offering the lowest efficiency will provide noticeable difference.

The most modern disk controllers come with a circuit for units with RAM cache so that the cache itself does not use the
memory that would be required by the programs. However, one can obtain similar results by loading programs flights
cache memory resident using the main system memory to cache units.

Source: Evolution of Computers

Hard Drive.

Hard Drive.

1 - A totally sealed metal housing protects internal components from dust particles that could penetrate
in the tiny space between the heads read / write and dishes, and cause damage to the magnetic coating of
dishes.

2 - In the lower part of the unit, one printed circuit board, also known as logic board receives commands
Controller, which in turn is controlled by the operating system. The logic board converts these commands into
voltage fluctuations that force the actuator to move the heads to read / write on the plate surfaces. The plate
also causes the rotational speed of the plates is constant and informs the drive heads when reading and when
record on the disc. In an IDE disk (Intcgrated Drive Electronics), the controller incorporates the logic board.

3 - A spindle connected to an electric motor rotates eight magnetically coated plates at a rate of thousands of
revolutions per minute. The number of plates of magnetic coating composition and determine the capacity of the unit.
Currently, the use dishes are almost always covered by an alloy of about 3 millionths of an inch thick.

4 - The actuator pushes and pulls the arm head group of read / write across the surface of the plates with precision
critical. It aligns the heads with tracks arranged in concentric circles from the surface of the dishes.

5 - The heads read / write connected to the ends of the movable arms sliding over the surface synchronized
the disk platters spinning. Heads record the data from the controller by aligning the magnetic particles in
surface of the plates, and then read the data to detect the polarity of the particles that were already aligned.

6 - When you or your program asks the operating system to read or write a file, the system prompts the
parent move their heads read / write to the file allocation table (FAT). The operating system
reads the FAT to determine which disk clusters that file is located or that disk parts are still available
to store a new file.

7 - A single file can be segmented into clusters positioned in hundreds of different dishes. The operating system
Guard the top of the file in the first block available that find the FAT. The FAT keeps track of chained
clusters occupied by the file, and each link leads to the next block that contains more pieces of the file.
Once the data from FAT have passed through the electronic part of the unit and the disk controller and returned to
operating system, this instructs the unit to skip their heads read / write on the surface of the plates,
reading or writing clusters on plates that are spinning in their heads.
After the operating system writes a new file on disk, the heads read / write FAT to return to
record the list of all clusters of the file.

Source: Evolution of Computers

How To Hard Disk.

How To Hard Disk.

The hard drive is a hard worker system PC. The dishes that store the data begin to spin rapidly
so the computer is turned on (except in the case of portable PCs, which periodically turn off the disk to save
battery). Each operation of the disk drive to read or write a file triggers a sequence of movements absurd - that
should be performed with microscopic precision by heads read / write. The settings of a hard drive obey
such accuracy - the intervals between the heads and the dishes are so small that they do not include a hair - is
fantastic as the unit can play so well its task without constant damage. Instead, it remains in order,
working for many years and presenting very few flaws.

The capacity, shape and performance of hard disk drives have changed dramatically since the onset of the first
IBM XT hard drive, in the early 80s. At that time, 10 megabyte capacity was considered generous.
The hard disk drive had 3 to 4 inches wide and occupies a space similar to a unit of
5 1/4 inches.
The access time of 87 milliseconds was then superfast, compared to the access time of floppy disk drives.
A decade later, the hard drives that hold 200 megabytes, with the smaller size of a disk drive
3 1/2 inches and access speed of 18 milliseconds, are cheap and supercomuns. More recent still, the models
removable 20 megabytes or more are no bigger than a matchbox. In the future, the size of the units
continues to decrease further as the storage capacity increases.

Certainly, one thing about the hard drives remain. Unlike any PC components that meet the
program commands without complaint, the hard drive vibrates and beeps while you are doing your job. Those
noise allow you to remember the hard drive as one of the few components in PCs that is both
mechanical and electronic. The mechanical components of the unit often make things happen.

Source: Evolution of Computers

Floppy Drive 3 1/2 inches.

Floppy Drive 3 1/2 inches.

1 - When a floppy disk 3 1/2 inches is inserted into the drive, it pushes the drive lever system. A
lever opens the flap (shutter) of the disc to expose the cookie - the layer of Mylar covering the both disk
sides with magnetic material that allows the recording of data.

2 - The other levers and gears move the two heads read / write up to almost touch the disk surface
(Cookie) on both sides. The heads, which are tiny electromagnets, the magnetic pulses used to change the orientation
of the metal particles contained in the disc surface.

3 - The circuit board unit receives signals from the controller card, containing the data and the instructions for these
data is written to disk. The circuit board converts the instructions into signals that control the movement of the disc and
heads read / write.

4 - If the signs contain instructions for the data to be written to disk, the circuit board finds in the first
place if there is no light visible through the small window that can be closed, located in a corner of
housing floppy. If the window is open and the light beam emitted by the diode can be detected by the photodiode
located on the opposite side of the disc, the unit will recognize that the disc is protected and refuse to write the data.

5 - The engine located below the disk rotates a shaft which engages a tooth in the center hole of the disc to make it spin.

6 - A stepper motor - which can rotate a certain number of times in either direction, according to signals
received from circuit board - moves a second axis having a spiral groove. Inside this groove, there is an arm that
binds to the head read / write. As the shaft rotates, the arm moves forward and backward, placing the
heads read / write on the disc.

7 - When the heads are properly positioned electrical impulses create a magnetic field in one of the heads
write data to the top or bottom surface of the disk. When the heads are reading data, they react to
magnetic fields generated by the hard metal particles.

Note - Despite the differences in size and casing, the floppy 5 1/4 inches is just a bigger version, more
less complicated and slow disk 3 1/2 inches. It has no door to be opened, but has a cutout side
to determine if it is protected against data recording. The heads read / write drive work the same
so that the smaller unit.

Source: Evolution of Computers