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
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