Floppy drives : 300 rpm; 200 ms seek time; 1 Mbits per Second transfer rate

The floppy disk interface uses what is considered, by most people, a truly strange cable. It is similar to the standard IDE cable in that it is usually a flat, gray ribbon cable. It is unusual in terms of the number of connectors it has and how it is used to configure the setup of the floppy disks in the system. The floppy cable has 34 wires. There are normally five connectors on the floppy interface cable, although sometimes there are only three. These are grouped into three "sets"; a single connector plus two pairs of two each (for a standard, five-connector cable) or three single connectors. This is what they are used for:

Controller Connector: The single connector on one end of the cable is meant to connect to the floppy disk controller, either on a controller card or the motherboard.
Drive A Connectors: The pair of connectors (or single connector in the case of a three-connector cable) at the opposite end of the cable is intended for the A: floppy drive. This is explained in more detail below.
Drive B Connectors: The pair of connectors (or single connector in the case of a three-connector cable) in the middle of the cable is intended for the B: floppy drive.

The reason that the standard cable uses pairs of connectors for the drives is for compatibility with different types of drives. 3.5" drives generally use a pin header connector, while 5.25" drives use a card edge connector. Therefore, each position, A and B, has two connectors so that the correct one is available for whatever type of floppy drive being used. Only one of the two connectors in the pair should be used (they're too close together to use both in most cases anyway). The three-connector cables are found either in very old systems or in ones where the manufacturer was trying to save a few pennies. They reduce the flexibility of the setup; fortunately these cables can be replaced directly by the five-connector type if necessary.

You will also notice that there is an odd "twist" in the floppy cable, located between the two pairs of connectors intended for the floppy drives. Despite the fact that this appears to be a "hack" (well, it really is a hack), this is in fact the correct construction of a standard floppy interface cable. There are some cables that do not have the twist, and it is these that are actually non-standard! What the twist does it to change the connection of the drive on the far end of the twist so that it is different than the drive before the twist. This is done to cause the drive at the end of the cable to appear as A: to the system and the one in the middle to be as B:.

Here's how it works in detail. Traditionally, floppy drives used a drive select (DS) jumper to configure the drive as either A: or B: in the system. Then, special signals were used on the floppy interface to tell the two drives in the system which one the controller was trying to talk to at any given time. The wires that are cross-connected via the twist are signals 10 to 16 (seven wires). Of these, 11, 13, and 15 are grounds and carry no signal, so there are really four signals that are inverted by the twist. The four signals that are inverted are exactly the ones that control drive selection on the interface. Since the signals are inverted, the drive after the twist responds to commands backwards from the way it should; if it has its drive select jumpers set so that it is an A: device, it responds to B: commands, and vice-versa.

Why on earth would anyone have wanted to do this? Basically, because it was a big time-saver during setup back in the days when it was quite common to find two floppy drives in a machine. Without the twist, if you wanted to use two floppy drives one had to be jumpered as A: and the other as B:. With the twist, you just leave them both jumpered as B:, and whichever one you put after the twist will appear to the system as A: because the control lines are inverted. If you want to change the setup so that the other drive is A: instead, you just switch the cable. If you only want one drive, you only use the connector after the twist. Large manufacturers, therefore, could arrange to have all of their floppy disks configured the same way without having to pull jumpers as the PC was assembled.

In order for this system to work, both drives must be jumpered as B: drives. Since the floppy cable with the twist is standard, this jumpering scheme has become the standard as well. Virtually all floppy disks that you purchase come prejumpered as B: drives so that they will work with this setup.

Some tips :
When you do a DIR command on a diskette, remove it and insert another, and get the same DIR listing from the first diskette, this is known as a "phantom" directory. The original files have just been trashed due to this! This is caused by line 34 on the floppy cable being defective & therefore not sending the disk change (DC) signal to the controller. Normally pressing the eject button sends the DC signal to the controller & causes DOS to flush out the floppy cache.

The temporary fix : If in DOS, use the Ctrl + C operation between disks.
The permanent fix : Make sure the jumper is on the DC jumper block. If it is, other soultions : replace the cable 1st, then if necessary : 1)make sure the cmos setup is correct, 2)replace the drive, 3)replace the system board, in that order.

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