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Wang 600 Calculator


  • This pages give a summary of the machine in its current state. For deeper dives see the other tabs and 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 in the Wang 300 series. This had been replaced with a more modern stack and RPN style interface in the 700 series but perhaps Wang was conscious of the large installed base of 300 series machines that were rapildly becoming obsolete. Owners of these would have been accustomed to the idiosyncratic keyboard interface and offering a familiar interface 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 very similar form factor, case and many shared internal construction methods. A single display register is provided with a Panaplex panel, Burroughs’ more modern replacement for the Nixie tube. 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 this seems to have been a common option.

Memory

The 600 was in development during probably the most impactful transition in memory technology - from physical magnetics like core and tape 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 was provided on the top of the machine to allow software packs using the new technology of MOS ROM ICs to attached. This may be the first example of plugin ROM packs, a technology that was to become ubiquitous within a decade. Interestingly, no examples of such ROM packs are known and surviving operators’ manuals do not make any reference to ROM packs. Perhaps mask-programmable ROMs proved to be uneconomical for what would have been very small production quatities.

Microcode and Microcode ROM

The 600 series microcode and the internal execution engine is very similar to that of the 700 series, constructed from SSI TTL logic and employing similar data paths and ALU/control functions. This provides an interesting illustration of benefits of microcode architecture. The investment in electronic logic design has been largely brought across from the 700 series, with a few changes to improve implementation such as moving to MOS RAM. New microcode delivers a completely different user experience and the microcode can be changed to improve that user experience as required. Changes in machine function no longer require changes to the machine hardware. 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 for the emerging microcode architectures and the 600 series illustrates both the magnitude of the initial problem and the manner in which problem finally disappeared. The 600 series required 2k x 42bits (nearly 11k bytes) of microcode store and this was initially provided with a wire braid ROM as used in the 700 series. This ROM was 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 as mentioned above was adopted for RAM in preference to magnetic cores (used in all previous Wang calculators and indeed invented by Dr Wang). One can imagine that there may have been difficult discussions about the emerging mask-programmable MOS 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, it would be interesting to know what type of ROM may be in other surviving machines and how ROM type may relate to build date.

In a further interesting irony, this machine has a failed wire ROM with two dead words. The ROM has been replaced with an emulation board using modern UVEPROMS and so has become a later-generation 600 with MOS ROM.

Printers, Plotters and Peripherals

The 600 series continued to support a wide range of peripherals including:

  • Mark Sense Card Reader for storage and entry of programs
  • Output IBM typewriter
  • Input/Output Typewriter
  • XY Plotter

Wang also provided software libraries to support the peripherals including 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.