3.6 Installing the Floppy Drive, Hard Drive, and CD-ROM
3.6.3 Connecting the floppy drive, hard drive, and CD-ROM to the system
The floppy drive, hard drive, and CD-ROM communicate with the rest of the system using ribbon cables. This section discusses the types of ribbon cables used as well as how to connect them to the various drives.

Characterizing Ribbon Cables
The floppy drive exchanges data with the motherboard devices, including the microprocessor, via a 34-pin flat ribbon (data) cable. The ribbon cable typically connects from a 34-pin male connector at the rear of the floppy drive to a 34-pin male connector on the motherboard. The cable plugs, drive connector, and floppy controller interface are all keyed, beginning at pin-1, for proper alignment. Usually, a red stripe on the edge of the cable identifies pin-1. Lining the red-stripe edge with pin-1 of the drive connector or drive controller interface assures a correct alignment.

Current system BIOS versions can support up to two floppy drives on one controller via a daisy chain cable arrangement. Cable pin-outs 10 through 16 are cross-wired between the middle drive connector and end drive connector, producing a twist that reverses the Drive Select (DS) configuration of the drive plugged into the end connector of the ribbon cable. The twist consists of 7 data wires. This feature, called cable select, automatically configures the drive on the middle connector as Drive B and the drive on the end connector as Drive A. This greatly simplifies installation and configuration of the floppy drives. In this example, only one 3.5" floppy (drive A) is being used.

Caution: Pin-1 on most floppy data connectors is usually on the near side to the power connector. However, floppy drives (normally 3.5 inch) from different manufacturers may have their data connectors reversed so that pin-1 (and the red wire on the ribbon cable) points away from the power connector. Also, some floppy disk drives are not clearly marked as to which is pin-1 on the data connector. In these cases an incorrectly oriented cable becomes immediately apparent on power up by the fact that the floppy drive LED light comes on immediately and stays on.

HDD and CD-ROM Cables – The hard drive and CD-ROM, just like the floppy drive, exchange data signals with the controller on the motherboard by means of a flat ribbon cable. The ribbon cable pin-outs and cable width are dependent on the type of interface. In this course, the IDE interface will be used. The ribbon cable used in this case looks physically similar to the floppy cable mentioned above but it is wider. Pin one is also identified by a red edge. However, an IDE cable typically has 40 pins and can also have two devices attached to it (like the floppy cable). In this case though, one device must be set as the master and the other as a slave using jumpers. A second cable is called IDE 2, and it can have a master and a slave. The cable connectors and plugs, just like the floppy cable, are keyed for proper alignment.

After becoming familiar with ribbon cables, the floppy drive, hard drive, and CD-ROM, these components can now be connected to the system board.

Connecting the Floppy Drive

Step 1 Identify the appropriate ribbon cable that goes with the floppy drive. It has a seven-wire twist towards one end and is smaller in width (34 pins) compared to the 40-pin IDE ribbon cable.
Step 2 Identify pin-1, the red edge of the cable, and align this with pin-1 on the rear of the floppy drive. Gently push on the cable connector until it is fully inserted. In most cases, the connectors are keyed. If any resistance is experienced as the cable is attached, then recheck the pin-1 alignment. Since this drive is being installed as drive A, be sure to use the connector past the twist in the cable.
Step 3 Now identify the floppy controller on the system board. Consult the motherboard manual to determine this. Attach the connector on the far end of the ribbon cable to the floppy controller on the board, making sure pin-1 is properly aligned for the cable and controller interface connectors.
Step 4 Work should be checked at this point, making sure that no pin is bent or displaced. If pin-1 has accidentally been reversed (not damaged), the drive will not work and the drive light will stay on all the time until it is corrected.

Connecting the Hard Drive and CD-ROM

Step 1 Identify the two 40-pin IDE ribbon cables that go with the hard drive and CD-ROM. These are wider than the floppy cable and have no twist at one end.
Step 2 Attach one end of one cable connector to the rear of the hard drive connector and one end of the second cable to the rear of the CD-ROM. The CD-ROM may have to be slid out a few inches to have enough access at the rear. Both cable connectors are keyed. Make sure that pin-1 is properly aligned for the cable and drive connectors.
Step 3 Now, attach the free end of the hard drive cable to IDE controller #1, the primary IDE, on the motherboard. Attach the free end of the CD-ROM cable to IDE controller #2, the secondary IDE, on the motherboard. Make sure pin-1 on each cable is aligned with pin-1 of the corresponding controller interface. Installing the hard drive and CD-ROM on separate IDE channels may improve performance.

Note: Pin-1 on both the hard drive and CD-ROM are usually located on the side nearest to the power connector. Sometimes it is labeled on the back of the hard drive. Conversely, pin-1 on the motherboard might not be properly labeled, so the manual will have to be consulted. The CD-ROM audio cable can wait until a sound card is installed.

Step 4 Check the work, making sure all cable connectors are properly seated, no pins displaced, and all pin-1s are aligned. If the hard drive cable is placed backwards, there may be some strange errors that make the new drive appear as if it has "died" already.