The floppy disk driver does not use the SSF or the elevator algorithm It is

The floppy disk driver does not use the ssf or the

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The floppy disk driver does not use the SSF or the elevator algorithm. It is strictly sequential, accepting a request and carrying it out before even accepting another request. In the original design of MINIX it was felt that, since MINIX was intended for use on personal computers, most of the time there would be only one process active. Thus the chance of a disk request arriving while another was being carried out was small. There would be little to gain from the considerable increase in software complexity that would be required for queueing requests. Complexity is even less worthwhile now, since floppy disks are rarely used for anything but transferring data into or out of a system with a hard disk.
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That said, the floppy driver, like any other block driver, can handle a request for scattered I/O. However, in the case of the floppy driver the array of requests is smaller than for the hard disk, limited to the maximum number of sectors per track on a floppy diskette. [Page 301] The simplicity of the floppy disk hardware is responsible for some of the complications in floppy disk driver software. Cheap, slow, low-capacity floppy drives do not justify the sophisticated integrated controllers that are part of modern hard drives, so the driver software has to deal explicitly with aspects of disk operation that are hidden in the operation of a hard drive. As an example of a complication caused by the simplicity of floppy drives, consider positioning the read/write head to a particular track during a SEEK operation. No hard disk has ever required the driver software to explicitly call for a SEEK. For a hard disk the cylinder, head, and sector geometry visible to the programmer often do not correspond to the physical geometry. In fact, the physical geometry may be quite complicated. Typically there are multiple zones (groups of cylinders) with more sectors per track on outer zones than on inner ones. This is not visible to the user, however. Modern hard disks accept Logical Block Addressing (LBA), addressing by the absolute sector number on the disk, as an alternative to cylinder, head, and sector addressing. Even if addressing is done by cylinder, head, and sector, any geometry that does not address nonexistent sectors may be used, since the integrated controller on the disk calculates where to move the read/write heads and does a seek operation when required. For a floppy disk, however, explicit programming of SEEK operations is needed. In case a SEEK fails, it is necessary to provide a routine to perform a RECALIBRATE operation, which forces the heads to cylinder 0. This makes it possible for the controller to advance them to a desired track position by stepping the heads a known number of times. Similar operations are necessary for the hard drive, of course, but the controller handles them without detailed guidance from the device driver software.
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