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Connectors and Jumpers
There are two main connectors that are used to connect the floppy disk to the rest of the PC. There are also jumpers that are used to configure the floppy, however in practice these are never normally touched. The drive select (DS) jumper is used to select whether a floppy is the A: or B: drive in the system, but the convention in the PC is to use the floppy cable to control which is the "A" drive and which is the "B" drive. Virtually all floppies come preconfigured as a "B" drive and the cable determines which one is seen as an "A" drive, instead of the jumpers. Similarly, some drive types have other jumpers to control their operation but they are virtually always left at their defaults.
Note: Some rare systems use
SCSI floppy disks, which have different jumpers.
One of the two connectors used to hook up the floppy disk is the power connector. There are two different types used; older 5.25" drives generally use the standard, keyed, 4-wire connectors that are used for hard disks, CD-ROMs and other devices. Most 3.5" drives use the smaller "mini" power connector. It is possible to buy adapters to convert from the larger size to the smaller, but all newer power supplies come with a mini plug specially included to power a 3.5" floppy drive. The power supply chapter discusses this in more detail.
The second connector is the data interface cable. 99.9% of floppy disks use the standard floppy interface, which uses a special 34-pin connector to attach to a floppy interface cable. The cable is important because of a special modification to it that allows it to control the drive letter of the floppies to which it attaches.
There are actually two different types of connectors. The older style uses a card edge connector on the drive; this is usually found on 5.25" drives. The newer style uses a 34-pin header much like the connector for an internal hard disk (but smaller). The latter type of connector is often not properly keyed to prevent incorrect insertion, so this can be a bit of a concern. Usually the indication that a floppy cable has been inserted backwards is the drive not working and the drive busy light coming on and staying on when the machine is booted. In the vast majority of cases reversing the cable will fix the problem and no damage will result to the drive from having been connected the wrong way initially.
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