Auto initial test.

Auto initial test.

1 - Ouando you turn on your PC, an electrical signal follows a path permanently programmed into the CPU to clean the data
registers left in the internal memory chip. The signal resets the CPU register called the program counter
to a certain number. In the case of TAs and newer computers, the number is F000. This number on the counter
tells the CPU the address of the next instruction to be processed. In this case, the address is the start of the program
startup (boot), permanently stored in the address F000 chipset ROM (read only memory)
containing the basic input / output system (BIOS) of the PC.

2 - The CPU uses the address to find and activate the program startup (boot) the ROM BIOS, which in turn,
activates a series of system checks, known as self-test or POST (Power-On Self-Test). First, the
CPU is checking itself and the POST program, through a code reading in various positions, comparing it
these checks are identical to the permanent records.

3 - The CPU sends signals through the system bus (bus) - where all the circuitry connect the components - for
check if they are all working.

4 - In older PCs that have a core programming language BASIC in ROM, this part of the code is given
while checking the timer (timer) system, responsible for timing and order of all functional operations
the PC.

5 - The POST tests the memory contained on the video card (display adapter) and video signals that control the monitor. He
causes the motherboard BIOS code becomes part of the total system BIOS and memory configuration. It is from
then you get to see something on the monitor of your PC.

6 - POST performs a battery of tests to see if the RAM chips are running smoothly. The CPU writes
data on each chip then takes a reading comparing these data with those sent originally. A counter memory
being read appears on the screen during this test.

7 - The CPU checks if the keyboard is properly connected and that no keys are pressed.

8 - The POST sends signals for specific paths through the bus (bus) to the disk drives and expects a reply
to determine which units are available.

9 - In AT computers and newer, POST test results are compared with the official record exists in
CMOS chip, which tells you which components are installed. The CMOS chip is a type of memory that does not lose its data
when you shut down the system or there is power cut: it is powered by a battery (battery). Any changes
the basic system configuration must be recorded in the CMOS configuration data, all PCs that have this
function. (Only the original PC and XT do not use the function CMOS.)

10 - In systems that contain components which include their own BIOS, as certain disk controller cards (disk
controller), the BIOS code is recognized and incorporated as part of the very system BIOS and memory usage.
The PC is now ready for the next step of the boot process (boot): load the operating system from disk.

Source: Evolution of Computers