DECmate was the name of a series of PDP-8-compatible computers produced by the Digital Equipment Corporation in the early 1980s. All of the models used an Intersil or Harris 6100 or 6120 microprocessor which emulated the 12-bit DEC PDP-8 CPU. They were text-only and used the OS/78 or OS/278 operating systems, which were extensions of OS/8 for the PDP-8. Aimed for the word-processing market, they typically ran the WPS-8 word-processing program.

Later models optionally had Intel 8080 or Z80 microprocessors which allowed them to run CP/M.

The range was a development of the VT78 which was introduced in 1978.

VT78

Introduced in 1978, this machine was built into a VT52 case and had an Intersil 6100 CPU running at 2.2 MHz. The standard configuration included an RX02 dual 8-inch floppy disk unit which was held by the pedestal the computer rested on.

DECmate

Introduced in 1980, this machine was built into a VT100 case. It had a 10 MHz clock, 32 KWords of memory. It was also known as the VT278.

DECmate II

As part of a three-pronged strategy against IBM, the company released this model at the same time as the PDP-11-based PRO-380 and the Intel 8088-based Rainbow 100. Like these other machines, it had a monochrome VR201 (VT220-style) monitor, an LK201 keyboard and dual 400K single-sided quad-density 5.25 inch RX50 floppy disk drives. It had 32 Kwords of RAM for use by programs, and a further 32 Kwords containing code which was used for device emulation. Code running in this second bank was nicknamed slushware, in contrast to firmware since it was loaded from floppy disk as the machine booted. It was also known as the PC278.

It could be expanded, either by adding another pair of 5.25 inch floppy disk drives, and it could also support either an additional pair of RX01 or RX02 8 inch floppy disk drives or a winchester disk.

It could also have a coprocessor board added, to allow it to run CP/M. There was a choice of three coprocessor boards, one with a Z80 and 64 KB RAM, and a choice of two boards with both a Z80 and an Intel 8086, the difference being that they had either 256 KB or 512 KB RAM.

Manufacture ceased in 1986. It was superseded by the DECmate III, introduced in 1984

DECmate III

This was introduced in 1984. It had a smaller system case, color monitor, 8 MHz clock, two 5.25-inch RX50 floppy disk drives, 32 KB user RAM, 32 KB system RAM. It was also known as the PC238.

DECmate III+

This was introduced in 1985 and withdrawn in 1990. It included a hard disk controller as part of the basic configuration. Otherwise, it was very similar to the DECmate III. It was also known as the PC24P.

Foibles

The DECmates were acceptable for word-processing, but due to various hardware quirks, were somewhat incompatible with many existing PDP-8 programs. The I/O interfaces worked slightly differently, which meant that most existing user and system programs could not detect Control-C and exit reliably. Every program, both user and system, had to be patched to fix this anomaly. Additionally, the CPU and screen update speeds were noticeably slower than the older PDP-8 systems.

References

• PDP-8 models, at faq.org
• DECmates at Columbia University
• VT78, Old Computers website
• DECmate I, Trailing Edge website
• DECmate II, Old Computers website
• DECmate II ROM contents, decoded and dissasembled by Charles J. Lasner
• DECmate III, Old Computers website
• DECmate III+, at machine-room.org
• PDP-8 Summary of Models and Options. faqs.org. Retrieved on 2008-07-13..