Hard Disk (hard drive) Operation

The disc platters are mounted on a single spindle that spins at a typical 10,000rpm. On EIDE and SCSI drives the disk controller is part of the drive itself. It controls the drive’s servo-motors and translates the fluctuating voltages from the head into digital data for the CPU. Data is recorded onto the magnetic surface of a platter in exactly the same way as it is on floppies or digital tapes. Essentially, the surface is treated as an array of dot positions, with each domain’ of magnetic polarisation being set to a binary 1 or 0. The position of each array element is not identifiable in an absolute sense, and so a scheme of guidance marks helps the read/write head find positions on the disk. The need for these guidance markings explains why disks must be formatted before they can be used. When it comes to accessing data already stored, the disk spins round very fast so that any part of its circumference can be quickly identified. The drive translates a read request from the computer into reality. There was a time when the cylinder/head/sector location that the computer worked out really was the data’s location, but today’s drives are more complicated than the BIOS can handle, and they translate BIOS requests by using their own mapping. Interleave Factor In the past it was also the case that a disk’s controller did not have sufficient processing capacity to be able to read physically adjacent sectors quickly enough, thus requiring that the platter complete another full revolution before the next logical sector could be read. To combat this problem, older...

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