IBM 5150 PC Technical Reference (6025005, August, 1981) (PDF)

5 1/4-Inch Diskette Drive Adapter
The System Unit has space and power for one or two 5-1/4" Diskette
Drives. The drives are soft sectored, single sided, with 40 tracks. They
are Modified Frequency Modulation (MFM) coded in 512 byte
~ sectors, giving a formatted capacity of 163,840 bytes per drive. They
have a track to track access time of 8 ms and a motor start time
of 500 ms.
The 5-1/4" Diskette Drive Adapter fits in one of the System Board's
five System Expansion Slots. It attaches to the two drives via an
internal daisy chained flat cable which connects to one end ofthe drive
adapter. The adapter has a second connector on the other end which
extends through the rear panel of the System Unit. This connector
contains the signals for two additional external drives, thus the 5-1/4"
Diskette Drive Adapter is capable of attaching four 5-1/4" drives, two
internal, and two external.
The adapter is designed for double density MFM coded drives and uses
write precompensation with an analog phase locked loop for clock and
data recovery. The adapter is a general purpose device using the NEe
IlPD765 compatible controller. Thus the drive parameters are
programmable. In addition, the attachment supports the drive's write
~ protect feature.
The adapter is buffered on the I/O bus and uses the System Board direct
memory access (DMA) for record data transfers. An interrupt level is
also used to indicate operation complete and status condition requiring
processor attention.
In general, the 5-1/4" Diskette Drive Adapter presents a high-level
command interface to software I/O drivers. A block diagram of the
5-1/4" Diskette Drive Adapter is on the following page.
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