Other hard drive kits were available, but were
less popular and therefore less available now.
Note:
Be sure your computer operates properly
BEFORE you begin the following modifications. If
your Monitor Rom is a version prior to 2.5,
you'll probably need to upgrade some parts on
the motherboard, including the Monitor Rom
(U190). If your motherboard is the old version,
85-2653, some circuit modifications may also be
needed. See the following text.
Note
: The term 'Z-100' in this article and
others published in the "
Z-100 LifeLine
" refers
to the class of Heathkit/Zenith computer and may
apply to either the Low-Profile H/Z-110 model,
which used a separate monitor, or All-in-One
H/Z-120 model, where a monochrome monitor was
self-contained.
The MFM ‘Winchester’ Hard Drive:
The following instructions cover installation in
both models of the Z-100 computer. The diagrams
will carefully show which model applies, when
necessary.
Important
: Early MFM hard drives are fragile and
can be damaged easily. In all hard drives, while
the drive’s platter is spinning, the read/write
heads float on a very thin layer of air, sep-
arating the heads from the platter’s surface.
However, the read/write heads on these early
drives came to rest on the surface of the disk
platter when rotation stopped. Any bumping,
knocking, or dropping may cause the heads to
bang against the surface of the platter. A
severe bump, especially while the platter is
spinning, could actually damage or gouge out a
small area in the platter and cause a “crash”,
where an important portion of a program is
unreadable and lost because the disk surface was
damaged. Further, the read/write head may also
be damaged.
For early hard drives, it is CRITICAL to run a
disk utility that parks the heads in an unused
portion of the disk - a storage or parking area
- before the heads come to rest. Such a utility
is SHIP, an external command packaged in CP/M
and MS-DOS operating systems. Later MFM drives
had an auto-park feature that placed the heads
down after the last usable sector of the drive,
in an unused area. But even then, the heads
could be damaged from a sudden drop.
MFM drives are recognized by their two ribbon
cable card edge connectors, one with 34 con-
ductors and the other with 20 conductors. RLL
drives also have these but the drive model
number includes an R. For example, an ST-138 is
an MFM drive, while an ST-138R is an RLL drive,
with different formatting, capacities, and
controller boards. ESDI drives also have similar
cable connections, but cannot be used.
MFM drives are becoming available from Ebay and
the used market, sometimes at ridiculous prices
and there is no guarantee that any of these will
work.
But let’s assume that you find one with possi-
bilities and want to try it. What is involved?
Caution
: You cannot just slap an MFM drive from
another computer into your Z-100 and expect it
to work, without completely reformatting the
drive. It will require low level formatting
using the Z-100 PREP command, partitioning using
the PART command, and a high level formatting of
each partition using the FORMAT command. These
commands are unique to the Heath/Zenith CP/M and
MS-DOS (now referred to as Z-DOS) operating
systems.
There are numerous manufacturers of MFM drives,
each with different sets of programming plugs,
jumpers, and terminating resistors. If you have
a specific brand that you can not figure out,
try emailing me at the “Z-100 LifeLine”.
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