I stumbled on this set of scans over at DigiBarn (a most excellent computer museum), a reprint (in the late '70s) of Imlac's brochures for their systems and configuration options. I thought I'd reproduce some of the text here, since it's pretty interesting (to me, anyway) and since a lot of this is completely new to me -- I've not seen it referenced anywhere.
OVERVIEW
Imlac Corporation (founded in 1968) is a manufacturer of interactive intelligent graphic display systems. It has marketed the PDS-1 Graphic Display Computer since 1970 and the PDS-4 system since 1974. The PDS systems are programmable stand-alone or terminal graphics processors. Internally, the systems consist of two independent processors which use system memory in common:
- The main processor (a minicomputer manufactured by Imlac), which performs file I/O, field calculation, and other support functions.
- The display processor, which may be programmed in its own Assembly language to generate the screen displays.
The basic PDS-1, which sells for $8,300, consists of a 15-inch display screen, an operator keyboard, 4K words of memory, the display and main processors, and an interface for telecommunications. A basic PDS-4, which sells for $17,300, consists of similar components, with a 17-inch screen, faster main memory, and a more powerful display processor. A full complement of software is supplied with all systems, including a FORTRAN compiler (disk system only), Assembler, linking programs, and debugging aids. Also available is a floppy disk system comprising a controller, interface, and up to four IBM 3740 compatible disk drives.
For systems sold with cartridge disks, Imlac provides a full disk operating system with file access facilities and support of the programming languages. For systems which use the telecommunication interface, a set of interactive operating software is available, including graphical terminal control programs on the PDS systems and a set of FORTRAN callable support subroutines for the host computer.
To date, some 600 PDS systems have been delivered. Table 1 presents the specifications of the systems.
[No, that's not a typo -- by 1977, Imlac Corporation had sold only six hundred PDS systems, total. Given Imlac's last gasp was in 1979, I can't imagine that many more than 1,000 Imlac systems were ever made. It makes me wonder how they managed to stay in business that long, the margins couldn't have been that high.]
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| Table 1 |
COMPATIBILITY
All peripherals of PDS Systems are compatible with all PDS mainframes, allowing upgrade from a PDS-1 to a PDS-4. PDS-1 software is also upward compatible with that of the PDS-4. However, the PDS-4 supports additional display generation commands and its software is not, in general, compatible with PDS-1 software.
For PDS systems which use telecommunications, Imlac provides software to communicate with most timesharing systems. Under local program control, the user may specify transmission speed, character parity, and character echoing. Emulators are also available for Tektronix 4010 and 4014 Graphic Terminals.
As part of its standard peripheral options, Imlac has developed a number of direct connection interfaces to most popular minicomputers and some mainframe computers.
PERFORMANCE AND COMPETITIVE POSITION
Imlac was one of the first companies to produce and market stand-alone intelligent graphic systems. The only product line of the company is and always has been graphic-based systems.
The principal difference between the PDS-1 and PDS-4 systems is one of throughput, or graphing rate, and graph sophistication. The PDS-4 uses main memory with a cycle time under 1 microsecond, where the PDS-1 uses 1.8-microsecond memory. A larger display screen is provided as a standard element of the PDS-4 than for the PDS-1, and the display processor of the larger system allows for twice the number addressable points in both the X and Y directions. The PDS-1 has one display intensity value, and the PDS-4 has sixteen (optional on the PDS-1), which may be associated with any figure on the screen under program control. Hardware blink and virtual paging are optional on the PDS-1 and standard on the PDS-4
A number of display options are available for the PDS-4 only: a special instruction set provides for display processor scaling, rotation, translation and windowing; an automatic increment feature allows rapid display of very compact data lists. Both units offer an arc generation hardware option and may support multiple independent display monitors.
Over the years, a number of competitors have entered the programmable graphic system market, but Imlac has maintained its position of offering programmable graphics systems at a low cost. To date the minicomputer based competitor with the closest price to the Imlac equipment is the Tektronix 4081 Interactive Graphic Computing System, priced at $27,000. Recently, microprocessor-based programmable graphic systems have also been announced, principally the Tektronix 4051 Graphic Computer System (priced under $8,000), but these devices do not have the display power or peripheral capability of the Imlac systems.
Generally, higher priced programmable graphic systems offer faster processors, faster display rates, larger display areas, or specialized functions such as windowing, reflections, circle and ellipse generators, or three dimensional software. To a certain extent, the relatively low price of the Imlac equipment may be attributed to the use of its own minicomputer.
USER REACTION
Users were interviewed from the engineering, electronics, and medical fields. They were unanimous in stating that the PDS systems had met their objectives, and had proven to be a cost-effective solution to the wide range of applications. Typical user configurations were basically of two sorts:
Most users programmed PDS systems in Assembly language or by using host facilities provided by Imlac. FORTRAN is usually preferred by users with disk systems; one user has developed a cross assembler for his host minicomputer. Another user found that the program editing software provded by Imlac was very good, and he uses it as a word processing system for manual documentation.
- A small PDS system configured (often by direct connection to a general-purpose minicomputer) as a smart graphic terminal.
- A stand-alone disk-based configuration, usually with some telecommunication connection to a remote host computer.
Equipment reliability was rated good to excellent by the users. A large number of them performed their own hardware maintenance; the rest used standard Imlac service contracts.
Engineering
One user, an engineering consultant, has a PDS-4 system with a disk and line printer. He uses the system to develop a series of power plant control displays for the electric utility market. The Imlac system was chosen over faster screen displays because of the amount of alphanumeric data which could be displayed on the screen, and it was selected over other graphics systems, such as Vector General, IDI, and Evans and Sutherland, on the basis of cost effectiveness.
The power plant displays make heavy use of both alphanumeric and schematic diagram data as control information for the plant operator. The development work done on the first PDS system was sufficiently successful; additional units were built to the firm's own specifications. Recommendations have been made to place the PDS in a number of power plant control rooms around the world.
Research
A large western university has a number of PDS systems installed in various departments; the bulk of the work is done in the field of medicine. The systems, both PDS-1 and PDS-4, are connected to a large central IBM computer, and typically use emulation software for IBM graphic devices such as the 2250. Here, the Imlac equipment was chosen for its cost effectiveness.
A gamut of both experimental and operational application is running on PDS systems: graphical data reduction of EEG recordings for brain function analysis, pulmonary physiology studies for emphysema research; a very large package of statistical programs used in such departments as mental retardation studies, radiation treatment planning, and an "excellent version of Star Trek." These units are mainly small configurations with few peripherals. The host computer is relied upon for application processing with only graph manipulation occurring at the PDS system.
Simulation Applications
A number of other users were employing PDS systems as graphic control terminals in simulation applications. Two users had flight training systems operational where the PDS system was directly connected to a general-purpose minicomputer. In both systems, the PDS was used as the instructor's display and was used to continuously update training history and simulated radar information.
Another PDS-4 is directly connected to a Data General NOVA minicomputer. It is used by the U.S. Navy to verify operational communications links and protocols. The screen is used in a fashion similar to the standard tactical display screens for exercising, emulating, and verifying communication traffic.
[I need to find a copy of that "excellent version of Star Trek." So much software lost to the ages.]
CONFIGURATION GUIDE[600,000 baud? It does look like it's technically possible to wire the RS-232 ports for just about any baud rate but somehow I'm skeptical...]
The standard PDS system consists of a display screen with display processor that shares memory with the minicomputer, a main processor (16-bit minicomputer), a keyboard, and an RS-232 interface.
The basic PDS-1G includes the graphic display processor, a 15-inch display screen (17- or 21-inch screens are optional), a minicomputer with 4,096 words of memory, an alphanumeric keyboard with programmable function keys, ROM bootstrap for program loading and an RS-232 interface for modems or asynchronous devices (75-600,000 baud). The PDS-1G-8 includes all of the above plus an additional 4,096 words of memory.
The basic PDS-4 includes a graphic display processor, a 17-inch display screen (15- or 21-inch screens are optional), a minicomputer with 4,096 words of memory, an alphanumeric keyboard with programmable function keys, a ROM bootstrap for program loading and an RS-232 interface for modems of [sic] asynchronous devices (75-600,000 baud). The PDS-4-8 includes all of the above plus an additional 4,096 words of memory.
The basic system may have the following added to them: memory up to a total of 32K words, three independent display monitors and keyboards, a number of specialized display options, and a variety of peripheral devices (a cartridge disc, a floppy disk unit (PDS-4), paper tape equipment, magnetic or cassette tape drive, a hard copy unit, printers or printer/plotters and a graphical digitizing tablet).
Mainframe
The central, or main, processor is a 16-bit minicomputer with a .99-microsecond (PDS-4) or 1.8-microsecond (PDS-1) cycle time. It includes 4,096 words as standard, and a maximum of 32K words (PDS-1G) or 64K words (PDS-4). The processor has one interrupt level; another interrupt level is added if a direct memory access (DMA) option is used.
The display processor operates on a cycle-stealing basis using the system main memory; its speed is governed by main memory speed on each model. Operationally, the main processor loads or constructs a display program for the display processor and instructs it to execute the display program. The display processor draws the graphic display, based on the contents of its current display program. The display generation occurs simultaneously with operations by the main processor.
Optional features may be selected for memory protection, floating point arithmetic, a real-time clock, a DMA channel (with additional interrupt), display arc generation hardware, scaling, rotation and windowing hardware (PDS-4 only), parallel or serial I/O channels, a programmer console, and special direct interfaces to a number of other computers.
PERIPHERALS
A variety of peripherals are available for the PDS graphic systems; Table 1 lists auxiliary storage limitations.
Cartridge Disk. The disk file system consists of a single disk drive of two platters, one fixed and one removable, with a total subsystem storage capacity of 10 megabytes. Data transfer is at the rate of 180K bytes per second, with a random access time of 35 milliseconds. Disk transfers occur through the system DMA channel. Systems with disks are provided with the Imlac Disk Operating System.
Magnetic Tape. Units are available to support both 1200- and 2400-foot reels, using 9-track tape recording at 800bpi. Transport speed is 12.5 or 37.5 ips.
Floppy Disk. Dual floppy disk drives may be attached to the PDS-4. The units operate across the DMA channel. This floppy disk system comprises a controller, interface, and up to four IBM 3740-compatible disk drives. Minimum system requirements for use with the system is 16K bytes of core memory.
Cassette. A read/write cassette drive is available at recording at 120 cps.
Paper Tape Equipment. A photoelectric paper tape reader, operating at 300 cps, and a paper tape punch, operating at 75 cps, are available.
Graphic Hardcopy Device. This optional unit creates a permanent exact copy of the display screen on an 8-inch-square sheet. It may be connected directly to the system display or driven as an independent display.
Digitizers. A data tablet with a 14- or 72-inch square surface is available, as well as a graphic mouse for the digitizing of input. Both a joystick and a lightpen are available.
Printers. Printers (132 column) operating at 30cps or 70 lpm are available. A 500 lpm printer plotter is also offered.
[I'd love to know what technology the "Graphic Hardcopy Device" used to make a copy of the display screen -- perhaps something similar to what Tektronix 40xx series terminals used?]
The last three pages contain a huge table covering all of the various options and their prices, which I won't attempt to recreate here. 16KW of memory cost an additional $6,500. The Floating Point Arithmetic module was $9,500 -- I'd love to know what that consisted of given that it was more expensive than a base PDS-1G at the time.
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