DECMATE WORD PROCESSORS
Introduction
The DECmate brand was the name given to a new series of PDP-8-compatible desktop computers produced by the Digital Equipment Corporation (DEC) in the late 1970s and early 1980s. The DECmate was released to compete in the word processing market. Several vendors had standalone word processing systems (e.g. Smith Corona XD-7000); pre-dating the release of word processing applications on desktops such as the IBM PC. DECmates were text-only systems and used the OS/78 or OS/278 operating systems, which were extensions of DEC's widely used OS/8 for the PDP-8. DECmates typically ran the WPS-8 word-processing program. Later models also ran the CP/M operating system using an optional Intel 8080 or Z80 processor add-on card. The DECmate was a refinement of the VT78 word processor, introduced in July 1977. All DECmates used an Intersil 6100 (later known as the Harris 6100) or Harris 6120 (an improved Intersil 6100) microprocessor which emulated the 12-bit DEC PDP-8 CPU. Some literature refers to the 6100 microprocessor as a gate array based implementation of the PDP-8 architecture. DECmates were consistently refined with each new model to occupy a smaller footprint.
The last model manufactured, the DECmate III+, only occupied a small desktop footprint but featured a floppy drive and a 20MB hard disk (MFM). 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 the IBM PC systems.
VT78
The VT78 was based on the Intersil/Harris 6100 microprocessor and packaged in a VT52 terminal case. The 6100 processor could run at 4 MHz, but in the VT78, it was only clocked at 2.2 MHz because of the speed of the DRAM used and the deliberate use of graded out chips. Using TTL MSI and LSI components, DEC could pack a system into the VT52's vacant space, allowing PDP-8 systems to compete with personal computers in the small business and office automation market. This was a natural follow-on to the desk-mounted workstation configurations in which the PDP-8/A was already being sold.
The VT78 was sold with 16k words of DRAM, leveraging the keyboard and display of the VT52 terminal. An RX01 dual 8" diskette drive was included, packaged in a pedestal under the terminal. The console (device 03/04) and the serial ports (devices 30/31 and 32/33) are compatible with the M8650 KL8E, with the latter extended to allow software controlled baud rate selection. There are two parallel ports; device 66 (compatible with the M8365 printer controller) and device 47, compatible with the nonstandard port on the M8316 DKC8AA. There is also a 100Hz clock compatible with the clock on the M8316 DKC8AA. The standard ROM boots the system from the RX01 after setting the baud rates to match that selected by the switches on the bottom of the VT52 case. This was a closed system, with few options. The base configuration was able to support two RX01 drives (later RX02), for a total of 4 transports. Various boot ROM's were available, including a paper-tape RIM loader ROM for loading diagnostics from tape. Another ROM boots the system from a PDP-11 server in the client/server configuration used by WPS-11.
Introduced
Last Shipped
Processor
Memory
Price
1978 1980 Intersil 6100 @ 2.2MHz 16K words $7,995
DECmate I
Based on the Harris 6120 microprocessor, packaged in a VT-100 terminal with keyboard and display. This machine was aimed primarily at the market originally opened by the VT78, using a new gate-array implementation of the PDP-8 under contract to Harris by DEC. The Harris 6120 was designed to run at 10 MHz. The new packaging was optimized for minimum cost and mass production. The DECmate I was sold with 32k words of memory, with a small control memory added to handle control/status, console device emulation and boot options. The console terminal keyboard and display functions are largely supported by code running in control memory (a less expensive alternative to dedicating hardware for this, as was done in the VT78). The DECmate I came with an integral printer port, compatible with the VT78 (device 32/33), and it had an RX02 dual 8 inch diskette drive, mounted in the short pedestal under the terminal/CPU box. A 100Hz clock was included, as in the VT78 and PDP-8/A.
This was a closed system, with limited options. Specifically, a second RX02 could be connected (or an RX01, because that had a compatible connector), the DP278A and DP278B communications boards (really the same board, but the DP278B had 2 extra chips), and the RL-278 disk controller, able to accommodate from 1 to 4 RL02 rack mount disk drives. When the DP278A option is added, additional routines in control memory come alive to handle terminal emulation and allow disk-less operation. The terminal emulator is an extended VT100 subset that is essentially compatible in 80 column mode. The DP278A option could support both asynchronous and synchronous protocols, and the DP278B could handle SDLC and other protocols. Various pedestal and desk configurations were sold for housing the RX01 and RX02 drives. There was also a pedestal version that was essentially a repackaging of the RX02 with either 2 or 4 new 8 inch disk transports.
Introduced
Last Shipped
Processor
Memory
Price
1980 1984 Harris 6120 @ 10MHz 32K words NA
DECmate II
Based on the same 6120 microprocessor as the DECmate I, this shared the same packaging as DEC's other desktops competing in the PC market, namely the Rainbow (8088 based) and the PRO-325 (PDP-11 based). This machine was introduced in order to allow more flexibility than the DECmate I and to allow more sharing of parts with the VT220 and DEC's other personal computers. Like the others it had a monochrome VR201 (VT220-style) monitor, an LK201 keyboard and dual 400K single-sided quad-density 5.25-inch RX50 floppy disks. The DECmate II was sold with 32K of program memory, plus a second full bank for dedicated control panel function emulation. Code running in the second bank is sometimes referred to as "Slushware"; it looks like hardware to the PDP-8 user, but it is actually device emulation software that is loaded from the boot diskette. An integral RX50 dual 5.25 inch diskette drive with an 8051 controller chip was included, along with a printer port, a 100Hz real-time clock, single data communications port and interfaces to the monitor and keyboard. The diskette drive can read single-sided 48 track-per-inch diskettes.
This was the most open of the DECmate systems, with a number of disk options: An additional pair of RX50 drives could be added, and with the RX78 board, it could support a pair of dual 8 inch drives, either RX01 or RX02. As an alternative to the RX78, there was a controller for an MFM hard drive. The interface to the RX78 board wasn't fully compatible with earlier interfaces to RX01 and RX02, and there was no way to have both an RX78 and an MFM drive. The MFM drive could be up to 64 MB, with 16 sectors per track, 512 bytes each and at most 8 heads and 1024 (or possibly 4096) cylinders. A power supply upgrade was needed to support the MFM drive. DEC sold this machine with 5, 10 and 20 MByte hard drives, Seagate ST-506, 412, and 225 respectively.
A graphics board supporting a color monitor could be added in addition to the monochrome console display; two variants of this board were produced during the production run, all slightly incompatible. A co-processor board could be added, with communication to and from the co-processor through device 14. DEC sold three boards, an APU board (Z80 and 64K), and two XPU boards (Z80, 8086 and either 256K or 512K). If these added processors are used, the 6120 processor is usually used as an I/O server for whatever ran on the co-processor. The XPU boards used a Z80 for I/O support, so 8086 I/O was very indirect, particularly if it involved I/O to a PDP-8 device that was emulated from control memory. Despite this, the DECmate version of MS/DOS was generally faster than MS/DOS on more recent 80286 and 80386 based IBM PCs because of effective use of the co-processors (but they couldn't run MS/DOS code that bypasses MS/DOS for I/O).
Introduced
Last Shipped
Processor
Memory
Price
1982 1986 Harris 6120 32K words $3,745
DECmate III
DEC discovered that the market for large systems was dominated by other products, and that the PDP-8 based products were rarely expanded to their full potential. Thus, there was no point in paying the price for expandability. The DECmate III, also known as the PC238, was sold with 32K of program memory, plus a second 32K full bank for dedicated control panel functions, an integral RX50 dual 5 1/4 inch diskette drive with an 8051 controller chip, a printer port, a 100Hz real-time-clock, a data communications port, and interfaces for the VR-201 monitor and keyboard. The following options were offered:
- PC23X-AB/LH -- a revised version of the Z80 based co-processor for the DECmate II, $430.
- PC23X-CA/LH -- a color graphics board largely compatible with the later DECmate II graphics board, $630
- PC23X-DA/LH -- a variant of the DEC scholar modem, $630
Introduced
Last Shipped
Processor
Memory
Price
1984 1990 Harris 6120 @ 8MHz 32K words $1,927 / $2,885
DECmate III+
This machine apparently represents the last gasp of the PDP-8, hunting for the remains of the ever-shrinking market niche that the earlier DECmates had carved out. The market niche was not there and the production runs for this machine were short enough that UV erasable EPROM technology was used where earlier DECmates had used mask programmed chips.
The DECmate III+ was sold with 32K of program memory, plus a second bank for dedicated control panel functions, an integral RX33 single 5 1/4 inch diskette drive with an 8751 controller chip, a printer port, a data communications port and interfaces to the monitor and keyboard. A hard disk controller compatible with the optional one on the DECmate II was included, supporting an integral ST-225 20 MB disk; it is likely that it can only handle up to 1024 cylinders, but it is otherwise compatible with the DECmate II.
The same co-processor option sold with the DECmate III was available, but because of the difficulty of adding a second floppy drive, this was rarely used (the Z80 was most likely to be used to run CP/M, but that system requires two drives to handle the installation procedure; an appropriately configured bootable image created on a DECmate II or III could run on a DECmate III+). The same graphics board as used on the DECmate III was also available. The circuit traces and connectors for the Scholar modem are present, but this option was never sold on the DECmate III+.
Introduced
Last Shipped
Processor
Memory
Price
1985 1990 Harris 6120 32K words $5,145
DECmate Hardware Guides
| Document Name | Order Part No. | Publication Date | Domain |
|---|---|---|---|
| DECMATE Word Processing Manual | AA-K663B-TA | January 1982 | WPS |
| DECMATE II Specification, Rev 4 | NA | January 1983 | HW |
| DECMATE II CP/M Technical Notes | NA | March 1996 | HW |
| IM6100 CMOS 12 Bit Microprocessor | NA | NA | HW |