It was an interesting idea in principle: augment the Beeb to allow it to run PC software and provide a low-cost, incremental path into acquiring a PC-compatible. And it is one of those things that seems reasonable on the face of it: you only need to add an additional component to an existing system and that saves you buying a completely new system.Well originally the 512 co-pro was slightly cheaper (and the Master 512 was smaller) than the PCs available at the time. Also some of us didn't have space for another large computer. It's just that Acorn's implementation was not well done.
Unfortunately, it suffered from some of the same economic obstacles as the Z80 Second Processor did with regard to that expansion providing genuine CP/M compatibility. In that case, CP/M really needed you to have disk drives, which added considerable expense in the first half of the 1980s, but up to a certain point in time, one could argue that generic CP/M machines were still more expensive and had poorer capabilities. Torch's Z80-based systems and expansions slid into this niche while it lasted, providing the arguably superior Beeb graphics and sound plus a workspace for programs somewhat larger than that normally available in many CP/M systems.
Similarly, with the Master 512, anyone wanting to run DOS software would have needed at least one disk drive, but by the time of the Master series, double-sided 80-track drives were a bit more reasonably priced. However, just as disk drives fell in price, related economic factors pushed down the pricing of PC-compatibles. Since the Master 512 card was £500 to start with, reduced quickly to £400, and only later discounted to far more reasonable prices, the total system cost was not especially competitive.
Then there were all the compatibility and performance issues. Torch had a crack at this kind of expansion with the Graduate and pretty much illuminated the likely issues, such as the Beeb video system not really keeping up with PC scene, and so you can read complaints about a lack of colours in 80-column modes where the PC is able to use its character generator instead of a bitmap mode. If Acorn had evolved the Master graphical capabilities just slightly, as discussed previously, that would have been less of an issue even by providing a four-colour 32K 80x25 "text" mode, for instance.
Compared to something like the Advance 86, which was introduced when disk drives and memory were pricey, where one might have bought the low-cost model and then upgraded, the Master 512 and Graduate approaches did at least provide a more viable upgrade path by building on a well-supported platform with a sizeable back catalogue of tape software. In contrast, the Advance 86 Model A was a weird, PCjr-like system that probably had orders of magnitude less support than even the PCjr. So, Acorn's approach was reasonable, if largely appealing to the company's existing users.
When Acorn first had a go at making a PC-compatible system - the ABC 300 series - competitors in the same class were also going to be several thousand pounds, and so they went for a higher end approach involving the 286, ostensibly to support Concurrent DOS. Keeping that solution might have mitigated compatibility issues somewhat because solutions like Merge, featuring on the AT&T PC 6300 Plus, permitted DOS program virtualisation with only a modest performance penalty. That might have overcome many of the compatibility issues.How would I do it now? Use a 286 or 386 processor not 186, include a bios to interface between pc and Beeb. Use FreeDos as OS.
Why Acorn went for the 186 is a minor mystery but it could have been related to power consumption, and I think the 186 was mostly aimed at, or successful in, embedded applications. When there was a PC podule planned for the Archimedes in its early days, Acorn suggested the 286 for that, but eventually decided that the product wasn't worth bringing to market. Eventually, as we know, the PC expansion card regularly featured in Acorn's ARM-based line-up, leading to the Risc PC and its compromised "dual-architecture" capabilities that also had a similar level of appeal to purchasers.
With all this said, however, I can understand the enthusiasm for the Master 512, and nobody really needs to justify doing whatever they like with it. That is largely what we are here for, after all.
Statistics: Posted by paulb — Mon Mar 25, 2024 5:19 pm