DECmate

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DEC VT78 Video Data Processor: a PDP-8 in a VT52 housing

DECmate was the name of a series of PDP-8 compatible computers manufactured by Digital Equipment Corporation (DEC) in the late 1970s and early 1980s. All models used an Intersil 6100 (later named Harris 6100) or Harris 6120 (an improvement on the Intersil / Harris 6100) as a microprocessor to emulate the 12-bit DEC PDP-8 CPU. The devices were operated exclusively in text mode and operated with the operating systems OS / 78 or OS / 278, both extensions of the OS / 8 of the PDP-8. Since the devices were aimed at the word processing market, they were mostly equipped with the WPS-8 word processing program. Later models had an optional Intel 8080 - or Zilog Z80 microprocessor and were able to CP / M perform. The computer series was a development based on the VT78, which was introduced in July 1977.

VT78

In July 1977 this system based on an Intersil 6100 processor with 2.2 MHz in a VT52 housing was introduced as the first of the series. The standard configuration included an RX02 double drive for 8-inch floppy disks , which served as a base for the computer.

DECmate

The successor to the VT78, and the first device under the "DECmate" series designation, was built into a VT100 housing and was introduced in 1980. The processor clock was now 10 MHz and the system had a memory of 32 kWwords , i.e. 12 times 1024 words of 12 bits. An alternative designation was VT278 .

DECmate II

In the battle for market share against IBM , DEC released this device in 1982, parallel to the PDP-11 -based PRO-380 and the Intel 8088 -based Rainbow 100 . The DECmate II looks like the Rainbow 100, but uses the 6120 processor internally. Another name for the DECmate II was PC278.

The DECmate II was equipped with the WPS-8 word processing system and the COS-310 operating system , under which the DIBOL programming language was available.

Like the other devices in the series, the DECmate II was equipped with a monochrome VR201 monitor in the style of the VT220 terminal, an LK201 keyboard and an RX50 double drive for single-sided 5.25-inch floppy disks with four times the storage density (400 KByte capacity).

The memory configuration consisted of 32 kwords of RAM for use by the program and another 32 kwords of software to emulate peripheral devices . Software in this second memory area was nicknamed "slushware" (from "slush" = "mud"), alluding to firmware ("firm"), as it was saved from floppy disk during the startup process Machine was read.

The model could be expanded many times. An additional double drive for 5.25-inch floppy disks was available as removable storage, as were the RX01 and RX02 drives for 8-inch floppy disks. Mass storage could be connected in the form of a Winchester drive. The machine was able to start the CP / M operating system via an expansion card with a coprocessor. There were three cards to choose from: all three had a Z80 processor, two also had an Intel 8086 processor. The memory capacity of the three cards was 64 kB, 256 kB and 512 kB RAM.

The production of the DECmate II was stopped in 1986, two years after the introduction of the successor model DECmate III.

DECmate III

Introduced in 1984, this model was externally characterized by a more compact housing and a color monitor, internally by a processor clock accelerated to 8 MHz. An RX50 double drive for 5.25-inch floppy disks and two banks of 32 kWwords each were unchanged. An alternative name for the device was PC238.

DECmate III +

One year after the DECmate III, an extension appeared that already had a controller for hard disks in the standard configuration , otherwise largely identical to the basic model. The DECmate III + was manufactured until 1990 and was also known as the PC24P.

PDP-8 compatibility

The DECmate computer series was suitable for word processing, but due to various weaknesses in the hardware, it was not completely compatible with existing programs for the PDP-8. This meant that a strong sales argument in favor of the DECmate series over IBM PC systems was no longer valid.

The background was that the input / output interfaces worked slightly differently, with the consequence that the system and user programs could not recognize Control-C as a termination signal and thus could not be safely terminated. Any software user and the system side, had individually by patch are adapted to the DECmate series.

In addition, the CPU and image structure were noticeably slower than with the PDP-8 systems that were already older at the time.

Individual evidence

  1. ^ A b John J. Snyder: A DEC on Every Desk? (en) . In: BYTE , June 1983, pp. 104-106. Retrieved October 3, 2019. 
  2. ↑ DECmate III. In: old-computers.com. Retrieved October 3, 2019 .

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