chao@cory.Berkeley.EDU (Chia-Chi Chao) (08/16/89)
Since there are many articles on adding a third floppy drive recently, I will share what I have done to accomplish this. It works, but not too elegant. Most floppy drives allow daisy chaining upto 4 drives through the use of DS0 to DS3, but IBM decided to use a twisted cable, leaving each drive as DS1. This is done so that the MOTOR ON signal can be controlled individually, but selecting the drive is this is really through the DS signal. I added a 34-"pin" edgecard connector to the non-twisted portion of the drive cable, so I can connect TWO B drives, selected only one at a time. The two DS1 shorting jumpers from the drives are removed. Selecting the drive is done manually through a switch. Four wires are soldered to the four terminals where the two jumpers usually go. Since two terminals (one on each drive, usually the closer one to the drive connector) go to the same wire on the cable, you only need a single pole, double throw switch, with the two common wires connected to the center pole. I use a toggle switch mounted on one of the unused expansion slot covers -- just drill a 1/4" hole on the metal plate. That's all for the hardware part. When I change the drive B, I just update the CMOS setup. If the CMOS setup is not correct for the drive, I get errror message when booting up. Since I don't use the floppies too often, this is not too inconvenient for me. I save some $$$ not having to buy a secondary drive controller, and have all three drives available -- 1.2M drive A, 360K and 1.44M switched as drive B. To the person asked about having two boot drives: You can add the edgecard connector to the TWISTED portion of the cable. Just make sure the ribbon cable is aligned properly when you clamp the connector. Now you have three sections to deal with. Chia-Chi chao@cory.berkeley.edu