Reviving a System One (was: How do I join the Cromemco group?)

[MikeS]

Hello again Malcolm,

 

Yes, Cromemco definitely was one of the better (and more expensive ;-) S-100 manufacturers; the only things I didn't like about the CS-1 were the noisy fans and that it's a little harder to work on than many other systems.

 

I think you'll find that the drives are Tandon TM100-2s. The little board on the back is the 'servo board' which contains the motor drive and speed control circuitry; documentation should be easy to find.

 

I should still have a spare STDC or two;  I'll have a look and if you haven't heard from me by the time you've got RDOS working, jog my memory. If/when I find one I could even put a system on line so you can test it yourself via Telnet and even play with Cromix a bit.

 

What version RDOS do you have, BTW?

 

Yes, we'd all love to see a reasonably priced STDC and/or solid state MFM drive emulator! There is at least one 'new' S-100 HD replacement (Monahan/N8VEM) but the trouble is that AFAIK there is very little information on the Cromemco drivers and the low-level protocols involved, so modifying the Cromix driver(s) would be a challenge; also, AFAIK unlike most MFM controllers the STDC reads an entire track at a time. Emulating the WDI-II might actually be easier, but someone would have to 'do it' in either case... ;-)

 

Re HD drives: in my experience (and that of many others) the 5.25 diskettes seem to actually be more reliable than the 3.5" HD diskettes and, as you say, unlike most 3.5" drives the drive speed is directly compatible with the 8" 360RPM. I think a lot of the 5.25HD drives' bad press has been from people mixing DD and HD formats and diskettes; I've had no problems with JU475s whatsoever, both in PCs and in my Cromemcos and other 8" replacements. Either way, using 3.5" or 5.25" HD disks (or 'real' 8" of course) seems to be much easier and reliable than the 360K format when it comes to creating disks from images on a PC, due to Cromemco's mixed-density format.

 

I believe there are at least two or three commercial versions of CP/M for the Cromemcos but I'm not sure where you'll find them. I hope you don't mind if I cc a copy of this reply to the list; perhaps someone else can send you a location or even the actual images. I believe Bill S has at least one working version, IIRC Robert K also has at least one version (Micah?), and I think Marcus also has one or more on his most excellent site.

 

And maybe posting this to the list will reawaken interest in that HD emulator... ;-)

 

Enjoy, and keep us posted.

 

mike

----- Original Message -----

From: Malcolm Macleod

To: MikeS

Sent: Monday, May 20, 2013 6:19 AM

Subject: Re: How do I join the Cromemco group?

Hi Mike,

Thanks for the fast and helpful response.

Yes, mine is a CS-1 with 2 full-height 5.25 drives.  I haven't yet pulled the drives from their mount to verify make/model, but they appear to be original (I can see Cromemco final QA stickers on them).  The drives each have a PCB mounted on their rear edge that I'm not familiar with.  Perhaps this is a data separator?

I am only in the initial stages of getting the CS-1 going.  I'm currently reforming the 7 large electrolytic capacitors (trickle charging) and have removed the key switch to get a key made for it.  Next step is to load-test the power supply, then see if I can get to an RDOS prompt.  I've got to say that I am really impressed with Cromemco's engineering and build quality.  My power supply is the non-HD model.

Perhaps my system once had an external hard drive.  I can't see any evidence of a past hard drive, but I agree it seems odd that someone would buy an expensive DPU/512k system with only floppies for storage.

Thanks for pointing me to the STDC.  That sounds like the solution I need.  I did some google searches and came up with an old posting of yours on vintage-computer.com.  I don't suppose you could still be persuaded to part with an STDC for $150 ??  If so, I'd definitely buy it.

Your suggestion to use 1.2M HD drives makes sense.  The only thing holding me back is my past bad experiences with reliability of this format.  I'd much rather use 1.44HD 3.5 drives (as they also use 500kb data rate), but of course the RPM and therefore track length are different.  SO... do you have any recommendations for 1.2M drives?  I think the Panasonic JU-475 has a fairly good reputation?

Longer term, an S-100 board that emulates the STDC and uses a SDRAM card would be perfect.  I'm seeing a few projects around at the moment that may be capable of being adapted to the Cromemco (for example - have you seen the new FreHD project for the TRS-80?), but it would be a long time before I could commit time to a project like that.  Do you have a rough idea as to how many Cromemco users might be interested in a project like that?

All things considered, I think I'll first attempt to use an early release of CDOS, so I have something that can run off the 5.25 390k drives (although I note your comment that this might not work with MSU "vertical" memory).  But Cromix is definitely where I want to be.

Do you have any pointers to where I can find real CP/M?  Is there an IMD image or similar that can be downloaded?  I got the impression this might have been an unfinished project.  Using CP/M instead of CDOS might have the advantage of overcoming the banked memory issues.

Thanks for the pointer to Marcus' site.  I've looked at parts of it before.  It has an amazing collection of Cromemco information.  It is fantastic to see that all this content has survived 30 years!

Regards

Malcolm

On Mon, May 20, 2013 at 5:03 PM, MikeS <dm...@torfree.net> wrote:

Hello Malcolm; welcome and congratulations!

I assume those are full-height floppy drives which would mean that you have a dual-bay CS-1 system, as opposed to a CS-1H, which only has one floppy drive and an internal bay for a hard disk; very odd that you would have 512K and a DPU in a floppy-only system, unless it had an external HD of some sort or someone replaced an internal HD with a floppy to fill the hole.

You might have a bit of a problem adding an internal hard disk as the power supply is slightly different. If you really want to add a hard disk you would probably be better off looking for an STDC controller and a compatible ST-412/506 type of drive (especially a fairly late relatively low-power model). WDI/-II controllers are easy to find but not only are they relatively slow, but they require an IMI-interface hard disk which is a pretty rare animal these days (especially a working one ;-)

Yes, you can run Cromix on a dual-floppy system although it would of course be pretty slow; all versions of Cromix can be configured for any combination of up to four 5.25 or 8" drives, but only the Z80 11-series would fit on two 5.25 disks. Other than installing a hard disk, one way of getting more capacity would be to replace the 360K DD drives with 1.2M HD drives which are functionally equivalent to 8" disks; if you have or can find 4 HD drives that would give you 4.8 MB of disk storage, almost equal to the 5MB hard disk that the CS-1H originally shipped with.

11 Series Cromix (up to 11-27 IIRC) is for the Z80 or the DPU in Z80 mode. I'm not sure if it's compatible with an MSU/MCU combo though.
20 Series was the first 68000 version, somewhat slower than the Z80 version despite using the 68000
30 Series was an improvement over 20 series; IIRC the 31 and later series required at least an XPU instead of the DPU.

The semi-CP/M-compatible CDOS is of course also an option, as is the 'real' CP/M.

Most Cromemco documentation and software is available here (if you haven't already found it):

http://maben.homeip.net/static/S100/cromemco/index.html

Enjoy! And, again, welcome!

mike

----- Original Message ----- From: <tjntjn...@gmail.com>
To: <cromemco+owners@googlegroups.com>
Sent: Sunday, May 19, 2013 8:47 PM
Subject: How do I join the Cromemco group?

Hi there.  I've recently acquired a System One in very nice condition, and am looking for a few pointers to help get me started.

I tried to join the Cromemco group, but I can't see a "join" button.  Is it by invitation only?  If so, do you mind sending me an invite.

My System One has:

- DPU
- TU-ART
- 512k MSU
- MCU
- 16 FDC
- Two 5.25" drives
- NO hard disk or WDI boards
- No manuals or software

I'm trying to figure out which operating system to get up and running. Cromix sounds like the best fit, but I'm unsure which version/image to use.  EG - are some only suitable for 8" drives?  I'm also unsure which Cromix versions work best with the 68000.

Looking through the documentation, it seems Cromix was mainly intended to be used on a hard-drive system.  Is running this from floppies feasible? I guess I'm trying to work out what's the best mix of software for this hardware.  Ideally, I'd like to run 3 terminals/users, and show how 3 concurrent users can program in BASIC/pascal/C etc.  I'm hoping to use it for an interactive vintage computer demonstration.

Of course, i'd love to get a WDI-2 and hard drive for it.  But I assume these are rarely available these days.

Thanks for your help - and feel free to post this to the Group.

Regards, Malcolm (Melb, Aust).