Question:
We all know that ST-506 hard disks are no longer made, and whilst you
can buy working old drives from various sources like EBAY, it would
seem like a much better idea to have some sort of converter that would
allow us to use IDE interface devices.
For example, IDE disks are very cheap, or we could choose to use a
flash memory card connected via an IDE card reader.
So after much Googling here are some potential solutions
a) Howards Super IO controller == S-100 card with IDE interfaces
working with CP/M
http://maben.homeip.net/static/S100/harte%20technologies/cards/Harte%...
b) MBIUSA's SCSI disk in a box with a ST506 interface out
http://maben.homeip.net/static/S100/disk/mbiusa/ST506%20disk%20emulat...
c) DATEX's flash based ST506 emulator in a half height drive
replacement form
http://maben.homeip.net/static/S100/disk/datastorage.fr/DTX300-ENG2.pdf
Answer:
Even if it isn't that much electronics, the demand is low, and
it takes some time to design and debug. They probably work a
little to satisfy the original specs. a little closer than
you actually require, too.
Another possibility is to match the S100 interface to the controller
card. IDE pretty much implements the original IBM ISA bus disk
controller interface, though without the address decode logic.
The data bus and a few lines of the address bus go right up the
cable (with a little buffering). If you could match that to the
S100 controller interface, you could do it at that level, instead
of the ST506 interface level.
That may or may not be easier than writing the Chromix driver.
It should take a lot less electronics than the ST506 interface.
On the one hand, the apparent question is "what can I use to covert an
old hard drive controller which used ST-506 type MFM hard drives, to
use more recent IDE hard drives, or to use Flash-type mass memory?"
That's a pretty tough technical issue. As has been said in reply, a
"converter" of that sort is not common and is expensive when
available. It's a complicated design, not at all easy in hardware, and
may require software changes anyway. It's on a par with "I want to run
my gasoline-type car on diesel. Is there a diesel to gasoline
converter?" Lack of customers, and the complications of design, are
why any available solutions are a few thousand dollars. That's
actually cheap, for the kind of support you'd need to make one of
these work in any running system.
On the other hand, the poster says they want to upgrade a Cromemco-
based, S-100 based system which runs Cromix (a Unix derivative) on an
ST-506 based controller; to use of a S-100 controller which uses IDE
hard drives, or solid state drives. That is a VERY different question,
and the hardware needed amounts to "just" another S-100 card, but more
software changes to Cromix. The benefit is that you'll have a
sustainable result, you'll be able to accomodate larger and a greater
variety of more recent drives, AND you may get performance improvement
(whatever that is worth).
Incidently, most flash memory is not generally appropriate for this
use, because it's generally slow and because in most cases it has
limited write cycles. Put another way, you'll wear out the flash cards
from all the writes you'll do in memory swapping in Unix-like
operating systems They work better for intermittant use and one-write,
many-read applications like cameras, audio players, etc. That said,
there ARE some solid-state hard drive capable technologies out there:
but not likely specific to MFM hard drive replacements. Easy question
to ask, tough to answer, depends on the particulars of use. CP/M
doesn't mind limited write cycles, it runs entirely in RAM!
As for IDE S-100 drive controllers, there are a few around but they
are not cheap. IDE came out just as S-100 was declining, if not after.
There are some IDE add-on designs (GIDE) and a bit of CP/M software
for them, which are Z80 specific. An IDE interface for S-100 is MUCH
easier than an MFM to IDE converter. But someone would have to write
the Cromix drivers and boot to accomodate the different drive, with
different cylinders, sector size, heads. If you have a Cromix system
in operation already, then someone can test an IDE controller and
drive on that system and develop such drivers, if they know how to do
that, if they have the time and interest.
I don't see any other choices. An expensive drive converter to IDE,
which may or may not work 100%; or make or buy an IDE S-100 card and
write some Cromix drivers for it. And I'd stick to hard drives, not
solid state stuff; in any event it's no easier to implement than an
IDE solution.
