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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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