Daves Old Computers -

Cromemco (named for CROthers MEMorial Hall - the Stanford residence where the founders lived), came into existance in the mid 1970s, and grew to become a major player in the S-100 business systems market.

Cromemco began by making S-100 boards. Their first system called the Z-1 was based on an IMSAI chassis with Cromemco boards, however they quickly moved on to building their own complete systems. Cromemco systems are known for their solid construction, massive power supply and large backplane. These are arguably some of the most reliable S-100 systems produced.

All Cromemco floppy disk controllers include RDOS, a disk monitor which resides in ROM at C000 - An interesting feature of the Cromemco FDC and KZ (ram) cards is that they work together to allow RDOS to be swapped out and a full 64k of RAM available when the OS boots (this is why most Cromemco systems have at least one Cromemco KZ memory card). The KZ cards extend this switching scheme further to allow up to 448k of memory to be physically present in the system.

Cromemco software includes CDOS, which is very much like CP/M, and Cromix, Cromemco's own multi-user unix-like OS. Cromix uses banked memory, and with 448k installed, can support up to 6 users (1 bank for the system, and 1 bank for each user).

Click any photo to view a large high-resolution image.

If you have read my Altair history, you may recall a reference to the Cromemco Z-2 that a friend of mine had. The Z-2 is a big rack-mount chassis with a 21 slot backplane, but no internal drives. The Z-2D is almost the same machine. The power supply has been mounted on the rear panel, and the slots moved back to allow room for two disk drives to be mounted on the front panel. Otherwise it is the same machine (and just as heavy). Here is a view of the back.

Installed S-100 Cards: Cromemco ZPU, 4FDC, 16KZ, TU-ART, and IMS 16K RAM(3).

Donated by Richard Parsons.

This is an early edition of the Cromemco System-3. Behind the front door we find that the card cage has been turned sideways and placed in sliders to allow it to be extended for access. This frees up enough room for two full sized 8" drives. Standard with the early System-3 were these Persci "dual" drives, effectively providing four 8" devices. These drives feature voice-coil head positioners and are VERY fast, although quite tempermental. Here is a view from the back.

Installed S-100 Cards: Cromemco ZPU, 16FDC, 16KZ(2), TU-ART and IMS 16K RAM(3).

Donated by Richard Parsons.

Here is a later edition of the System-3. The slots in the door are gone, allowing the troublesome Persci drives to be replaced by more generic Tandons. This unit also features an internal hard drive. The power supply has been redesigned to be easly adjustable for other countries, and the back panel has been modified to allow an insert with more I/O connectors. The card cage is pretty much unchanged.

Installed S-100 Cards: Cromemco ZPU, 16FDC, 256KZ(2), TU-ART(3), PRI and WDI-II.

Cromemco employed these "Mechanical Nightmare" PERSCI 8" drives in their early systems. These drives use a voice coil head positioner, and are very fast - when they work! Running two disks on a single spindle, with individual motors to load and unload the disk (it even slides it out of the slot for you), and containing several boards full of electronics, they gained a reputation for unreliability and were often replaced by standard drives. But - before the availability of hard disks, these were the only microcomputer mass storage device fast enough to run a multi-user Cromix system.

The PERSCIs were also available as the PFD external drive unit. Here is a view of the back.

Early version System-3 Final inspection report (72k JPG)
Cromemco System-3 Instruction manual (4.5MM PDF)
Cromemco C-5 terminal Technical Reference Manual (4M PDF)
Cromemco RDOS 1.0 Instruction manual (2.5M)
Cromemco Early CDOS Users manual (1.8M PDF)
Cromemco Later CDOS Users manual (2.7M PDF)
Cromemco C-5 terminal Technical Ref. Manual (4M PDF)
Cromemco HD-20 hard drive Documentation (650k PDF)

Cromemco Advertisements from late 70's

(Approx 150k .JPG each): Z-1, Z-2 page1/page2, Z-2D, Z-2H, System-3 page1/page2, Z-Family, ZPU, 4FDC, 8K-Bytesaver, Joystick, Multi-user, Cromix.
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Copyright 2004-2005 Dave Dunfield.