Wang 600 Calculator
- This page describes the machine in its current state. For deeper dives see the links above, including the complete Machine Log.
The featured machine is a model 600-6TF, serial CC 2001. This is a mid-specification machine with optional integrated printer and RAM expansion to 2k x 4 bits(!). The final inspection label is illegible but the PCBs are mostly stamped with dates in May 1972 and the chassis inspection date is likewise May 1972.
The 600 series was introduced in 1972 so this appears to be an early example. The Wang 600 (and 500) series followed after the 700 series, despite having ’earlier’ model designations. The 600 reverted to the “right and left adder” keyboard interface introduced in the mid 1960s for the Wang 300 series. The 700 series had a more modern stack and RPN-style interface but perhaps Wang was conscious of the large installed base of 300 series machines that were becoming obsolete in the early 1970s. Their users would have been accustomed to the idiosyncratic 300 series interface and offering something familiar may have helped to keep those customers in the Wang camp rather then have them consider other vendors.
The 600 otherwise has a close resemblance to the 700 series with a nearly identical case and many shared internal construction methods. The single-line display uses a Panaplex panel, Burroughs’ more modern replacement for their Nixie tube technology. The casette drive is retained for program and data storage, as are the two rear I/O connectors. The 24-pin rear connector is compatible with 300-series peripherals and this too may have helped to retain 300 series customers. A numeric printer could be fitted into the space left vacant by simplifying the displays and seems to have been a very common option, as seen in the current machine.
Memory
The 600 was in development during perhaps the most impactful transition in memory technology - from physical technologies like magnetic core and delay lines to solid-state microelectronic RAM and ROM. The 600 machines were the first Wang machines to abandon magnetic core RAM in favour of ICs, using early Mostek MK4008 1024 X 1 DRAMS. Three RAM levels were available:
- 1k x 4 to give 312 program steps and 55 storage registers,
- 2k x 4 to give 824 steps and 119 registers and
- 4k x 4 to give 1848 steps and 247 registers.
A connector on the top of the machine allows software packs of MOS ROM ICs to be attached. This may be the first example of plugin ROM packs, a technology that was to become widespread within a decade (and perhaps a missed opportunity for Dr Wang to gain another fundamental industry patent). Interestingly, no examples of such ROM packs are known and surviving operators’ manuals do not make any reference to specific ROM packs. Perhaps mask-programmable ROMs proved to be uneconomical for what would have been quite small production quatities.
Microcode and Microcode ROM
The internal execution engine of the 600 series is similar to that of the 700 series, employing similar data paths, ALU/control functions and also being constructed from SSI TTL logic. This provides an illustration of the benefits of microcoded hardware architecture. The investment in electronic logic design has been largely brought across from the 700 series, with improvemrnts such as MOS RAM and hardware support for subroutines. The microcode language is therefore similar to the 700, giving the microcode developers a head start. The 600 series microcode takes this similar underpinning and delivers a completely different user experience, and one that can be changed to improve the user experience as required. Changes in machine function no longer always require changes to the machine hardware and equally, if changes to hardware become necessary users can be shielded by adusting the microcode to preserve the original functionality.
ROM storage was the limiting factor as microcoded architectures emerged and the 600 series illustrates both the magnitude of the initial problem and the manner in which that problem finally disappeared. The 600 series required 2k x 42bits (nearly 11k bytes) of microcode store, a very large amount of ROM storage in the early 1970s. This was initially provided with a wire braid ROM as used in the 700 series. Wire braid ROM is large, fragile, costly to build and fiendish to repair.
Microelectronic memory technology was in active development at the time the 600 series was in design and semiconductor RAM was adopted in place of magnetic core that had been invented by Dr Wang and used in all previous Wang calculators. Perhaps there were difficult discussions about the emerging semiconductor ROMs and their ability to replace the wire braid ROM. 600 series machines were released with wire braid ROMs but a MOS ROM replacement was also designed. DoPECC’s machine is an early build date and has a wire braid ROM but MOS ROM machines are also known. It would be interesting to review the build dates of known machines to determine when the change may have been made.
This early generation machine CC 2001 has in fact come the full circle since its wire ROM has failed, with two dead words. The ROM has been replaced with an emulation board using modern UVEPROMS and so it could be said to have become a later-generation 600 with semiconductor ROM.
Printers, Plotters and Peripherals
The 600 series continued to support a wide range of peripherals inherited from the 300 and 700 ranges including:
- Mark Sense Card Reader for storage and entry of programs
- Output IBM typewriter
- Input/Output Typewriter
- XY Plotter
- ‘Classroom Display’ - a large display that replicated the calculator display
Since the era of the LOCI-2 Wang had published and supported a wide ranging software library for their calculators. This continued with the 600 series and libraries to support the peripherals included a sophisticated graphing package that could use the typewriter or XY plotter and was able to scale data, draw axes and label plots and points.
User manuals for some of this software may be found in the Data section.