UPGRADING REPAIRING PCs

146
Chapter 5—Floppy, Removable, Tape, and Flash Storage
Don’t Use a Floppy Drive While Running a Tape Backup
About the only circumstance that would cause a hardware conflict
is the use of a floppy drive while a tape backup is running. While
most high-capacity tape backup drives today no longer use the
floppy interface, they still often use DMA 2 for fast data transfers.
Because DMA transfers are not checked by the CPU or any other
part of the system, simultaneous use of DMA 2 by a tape backup
and a floppy drive can easily result in data loss on either or both
media types.
Disk Drive Power and Data Connectors
Two sizes are used for disk drive power connectors. Figure 5.3
shows the original “Molex” power connector used on 5 1/4-inch
floppy drives. Most 3 1/2-inch floppy drives and tape backups use a
smaller connector, but either size normally has the same 4-wire
pinout shown in the figure.
4
(+12V) Yellow
(Gnd) Black
(Gnd) Black
(+5V) Red
3
2
1
1 2 3 4
Figure 5.3 A disk drive female power supply cable connector.
Some 3 1/2-inch tape drives come with an extension cable with
only two wires: a ground wire (black) and a +5v wire (red), because
their motors use the same +5v power as the logic board does.
Figure 5.4 shows a typical 5-connector floppy data cable. Typically,
the 5 1/4-inch edge connectors are seldom used today, unless a
3 1/2-inch drive has a pin-to-edge connector adapter attached.
Table 5.1 compares floppy and hard disk ribbon cables.