DECmate

"VT78" redirects here. For the highway, seeVermont Route 78.

DECVT78 Video Data Processor: a PDP-8 built into a VT52 body

DECmatewas the name of a series ofPDP-8-compatible computers produced by theDigital Equipment Corporationin the late 1970s and early 1980s. All of the models used anIntersil 6100(later known as the Harris 6100) or Harris 6120 (an improved Intersil 6100) microprocessor which emulated the12-bitDEC PDP-8 CPU. They weretext-onlyand used the OS/78 or OS/278operating systems,which were extensions ofOS/8for the PDP-8. Aimed at theword processingmarket, they typically ran theWPS-8word-processing program. Later models optionally hadIntel 8080orZ80microprocessors which allowed them to runCP/M.The range was a development of the VT78 which was introduced in July 1977.

VT78

Introduced in July 1977, this machine was built into aVT52case and had anIntersil 6100microprocessor running at 2.2 MHz. The standard configuration included an RX02 dual 8-inch floppy disk unit which was housed in the pedestal that the computer rested on.

DECmate

Introduced in 1980, this machine was built into aVT100case. It had a 10 MHz clock and 32 Kwords of memory. It was also known as the VT278.

DECmate II

As part of a three-pronged strategy againstIBM,the company released this model in 1982 at the same time as thePDP-11-basedPRO-350and theIntel 8088-basedRainbow 100.The DECmate II resembles the Rainbow 100 but uses the 6120 processor. Its two operating systems are theWPS-8word processing system, and theCOS-310 Commercial Operating SystemrunningDIBOL.Like the others it had a monochrome VR201 (VT220-style) monitor, anLK201keyboard and dual 400 KB single-sided quad-density 5.25-inch RX50floppy diskdrives. 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 tofirmwaresince it was loaded from floppy disk as the machine booted. It was also known as the PC278.

The model 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 aWinchester disk.It can also have a coprocessor board added, to allow it to runCP/M.There was a choice of three coprocessor boards, one with aZ80and 64 KB RAM, and a choice of two boards with both a Z80 and anIntel 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 ahard disk controlleras part of the basic configuration. Otherwise, it was very similar to the DECmate III. It was also known as the PC24P.

PDP-8 compatibility

The DECmates were acceptable for word-processing, but due to various hardware quirks, were somewhat incompatible with many existing PDP-8 programs, largely eliminating one potential advantage of the DECmate series over theIBM PCsystems. TheI/O interfacesworked 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.

External links

• PDP-8 models,at faq.org
• DECmates at Columbia University
• DECmate I,Trailing Edge website
• DECmate II ROM contents,decoded and disassembled by Charles J. Lasner
• "PDP-8 Summary of Models and Options".faqs.org. 2001-06-08.Retrieved2008-07-13.