DOS and Windows operating systems can recognise a Floppy Disks format and will read from, and write to, almost any disk format. Over the years as Floppy Disk technology has improved, DOS has followed this evolution and quite a few disk formats have resulted. The first IBM PC's used a single sided floppy disk drive. Sectors are numbered from 1 and there can be 8, 9, 15, 18 or 21 sectors per track.Tracks are numbered from Zero and can be a max.Tracks (also referred to as cylinders) are concentric circles around the disk, and each track is divided into sectors. The surface of a Floppy Disk is divided into Track's, Sector's and Side's. Most 3.5 inch Floppy Disk Drives only require a +5 volt supply. The 5.25 inch Floppy Disk Drives require a +12 volt and a +5 volt supply. It is easy to re-assign the A: and B: drives in modern PC computers. Most cables suppled with modern hardware have four connectors on the floppy drive end of the cable with a 34 pin edge connector and a 34 pin header connector for each drive. This standard 34 wire Floppy Disk Drive Interface cable used in most PC computers has Drive A:, as the drive at the end of the cable, and drive B: further in, before the twist. Most PC Computers use a strange standard interface cable originally used by IBM, where each drive is selected as the second drive and a twist in the cable transposes the control signal between one drive and the next. The original way the drives were meant to be configured was to select one drive as the first drive and the other as the second drive, via the jumpers on the drive. In a PC computer the first drive is called A: drive and the second drive is called B: drive. Floppy Disk Drives have drive select jumpers on them that configure the drives as either first or second drive. The floppy drive interface can control two drives and the interface cable has two sets of control signals - one for each drive. 5.25 inch drives use an edge connector on the drive and the 3.5 inch floppies use a 34 pin header (pin) plug. The image at the right shows a typical direct drive motor that rotates the floppy disk media.įloppy Disk Drives require an interface circuit to interface them to the computer bus and the "standard" interface uses a 34 wire ribbon cable. An alignment of the head assembly can be performed with the aid of digital alignment disk but is not usually cost effective. A magnetic head assembly is moved back and forth across the surface of the disk by a stepper motor and must be aligned to very close tolerances in relation to the centre of rotation of the floppy disk. The Floppy Disk is rotated at 300 RPM for normal disks (DD) and 360 RPM for high density disks (HD). Floppy Disk Formats Phil Storrs PC Hardware book DOS Computers and floppy disk drives Floppy Disk Drive Mechanics.
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