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4.1 Controller Description
The EVERDISK subsystem comes mostly with the EV-391
controller board. The board is two-third sized, and is NOT
AT-compatible. The EV-391 controller uses MFM encoding,
which records 17 sectors per track on a hard disk
compatible with the ST506 specification. The EV-391 can
operate two drives, even if the drives have a different
number of heads and cylinders. The EV-391 has an optional
37-pin connector on the board's mounting bracket, which
allows the installation of an external hard disk drive
subchassis compatible with the ST506 standard.
Some EVERDISK subsystems are delivered with the EV-392
controller board. The EV-392 is similar in size to the EV
391 controller, but the EV-392 uses RLL (2,7) encoding,
which records 26 sectors per track on a hard disk
compatible with the ST412 specification. Drives connected
to the EV-392 MUST be RLL (2,7)-qualified.
EVERDISK subsystems can also be delivered with the EV
390 controller. The function of the EV-390 is similar to the
EV-391, but the EV-390 is a full-sized controller board that
can also control up to four 360KB-capacity floppy disk
drives in addition to controlling two hard disk drives. The
floppy disk section can be disabled by removing the jumper
shunt from the jumper block marked WlO (see Figure 4 for
the location of the WlO jumper block on the EV-390 board).
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