"Outline specification for the BBC MICROCOMPUTER system"

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Richard Russell
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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Mon Oct 10, 2016 5:17 pm

paulb wrote:Also interesting is Research Machines' absence from the meeting participants. Did they (or Sinclair) ever formally participate in the process?

Seven companies were contacted by the BBC, of which six actually submitted proposals: Acorn, Nascom, Newbury, Sinclair, Tangerine and Transam. It's quite possible that the seventh company might have been RM, but unfortunately none of the contemporary documentation I have mentions who it was. Of the six companies which submitted bids, three were then shortlisted: Acorn, Newbury and Tangerine. That Sinclair didn't even get onto the shortlist was a point which was made by the BBC when Clive later complained bitterly about the decision to choose Acorn.

As far as Research Machines is concerned they did of course eventually realise how important it was to have some degree of compatibility with the BBC Micro, which worked very much in my favour because they paid me a not-inconsiderable amount of money (at least, as it seemed to me at the time!) to supply them with my Z80 version of BBC BASIC for the RML 480Z.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby sweh » Mon Oct 10, 2016 7:38 pm

paulb wrote:An interesting tangent from that article is the High Level Hardware Orion, however.

The HLH Orion was the second Unix machine I ever used, at the Oxford Nuclear and AstroPhysics Lab (NAPL). The Oxford microcomputer society had permission to use them (there were 2). I guess they must have been Clipper based 'cos they had a 4.2BSD basis. To keep on topic, the Orion room used BBC Micros as terminals, running UTE5 ("Unix Terminal Emulator") - a home grown ROM written by Dr Clive Rogers, who ran the lab.
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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Commie_User » Mon Oct 10, 2016 10:18 pm

Richard Russell wrote:Seven companies were contacted by the BBC, of which six actually submitted proposals: Acorn, Nascom, Newbury, Sinclair, Tangerine and Transam. .. That Sinclair didn't even get onto the shortlist was a point which was made by the BBC when Clive later complained bitterly about the decision to choose Acorn.




Well there it is, we have our answer right here. Fantastic!

Though I'd love to be in the room to witness a skilled interrogator get the full facts from an evidently clammed Sinclair!

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby BigEd » Tue Oct 11, 2016 9:11 am

I've a feeling I've seen Sir Clive speak out on video about the decision-making process, but haven't been able to find it. I did find this quote though, apparently from the August 1981 Your Computer, as reported by Jimmy Maher:

“When you have a company like ours, which is easily dominating the whole of Europe in personal computers, we believe we have done a very important job in popularizing computers. It is a real disappointment to have your own national broadcasting corporation completely ignore you.”

“What the BBC is doing, it is doing badly and it is damaging the whole progress of computers in this country. We have put a new version of BASIC into our machines. It has been highly praised in the UK and abroad, because of its editing facilities. We developed into it features such as single-keyword entry. None of that is in the BBC version.”


Nearby Jimmy writes about the BBC's decision-making process - it's a telling which doesn't make the process look nearly as fair and organised as the impression we get from Richard's documents. But either way, Sinclair didn't win and Commodore didn't stand a chance.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby paulb » Tue Oct 11, 2016 10:48 am

BigEd wrote:Nearby Jimmy writes about the BBC's decision-making process - it's a telling which doesn't make the process look nearly as fair and organised as the impression we get from Richard's documents. But either way, Sinclair didn't win and Commodore didn't stand a chance.


I think it has always been acknowledged that there were effectively two phases of the procurement: the one where the Newbrain was the only real candidate (arguably through the usual means of fine-tuning the process), and the one where the BBC had to go looking for alternatives.

What is still quite interesting, and something that is related to Research Machines and their lack of interest, is how the established computing/equipment companies like ICL were never anywhere near any of this (or so it would seem). One might have thought that they would have been in a reasonable position to offer something, or just collaborate with the various participants, if only because of their capabilities in getting things made and deployed at some kind of scale.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Tue Oct 11, 2016 11:46 am

BigEd wrote:it's a telling which doesn't make the process look nearly as fair and organised as the impression we get from Richard's documents.

That article completely glosses over the process of asking seven different manufacturers to bid, shortlisting three and then finally selecting one (for which I have documentary evidence, some presented here, and was personally involved with). Rather it falsely suggests that the selection of Acorn was some cosy arrangement between John Radcliffe and Chris Curry, and that nobody else had a chance.

The truth is that when it became apparent that the Newbrain was unlikely to meet the BBC's needs, John Radcliffe and the then project team decided that they must open up the contest to other manufacturers, and also broaden the range of experts advising them in the choice. Thus it was that at the end of 1980 John Coll's specification was sent to the seven companies, and BBC Engineering (particularly my department, Engineering Designs Department) were brought into the project.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby BigEd » Tue Oct 11, 2016 11:50 am

It might be worth leaving a comment there, perhaps with a link to this thread.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Commie_User » Tue Oct 11, 2016 1:57 pm

Old Sir Clive really is a Grumpy Gus, isn't he. My distinct impression is that he could never see further than his own corporate culture of cheap, cheerful and moderately flexible equipment, where the concept was bigger than the product. The watches and televisions were brilliant affordable firsts, yet left much to desire.

Looking at Acorn, I always had the impression that the Beeb was as catered to the tasks as much a concept. Hence their apparent ability to have machines closer to the BBC's own requirements by default. And a squad of boffins to back it up with as much of the vital fresh ideas and insights as possible. Men to take your hat off to in carrying tech forward as much as expanding the existing idea.

That's my view from here.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Tue Oct 11, 2016 3:04 pm

BigEd wrote:It might be worth leaving a comment there

Done, although whether anybody will moderate and approve it four years after the article appeared is another matter!

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby 1024MAK » Tue Oct 11, 2016 3:26 pm

As always with complex issues, there are many variables at play. Acorn's objective with the Proton was completely different to Sinclair's with the ZX80, ZX81 and ZX Spectrum. And all the other manufacturers all had their own ideas of the market. All made mistakes. And ironicly, the longest lasting eight bit manufacturer was Amstrad, who were late to the party. Although their last eight bit machine (PCW) was sold as a Word Processor...

For me, I was never that bothered about having a ZX Spectrum at home, but using a BBC B at school (I loved both). And love or hate Sinclair and his low cost range, it got a lot more people involved in computing than otherwise would have happened.

And to be fair, the specification that the BBC produced although possible at the time, was always going to result in a product that would cost significantly more than the Sinclair machines. I mean, just trying to make a reasonable priced Z80 based computer to those requirements given the cost of ROM and DRAM at the time would have given any engineer a headache...

I think Acorn had two things going for them. First, they had a design that was close-ish to the specification. And two, they were willing to put the work in to build a prototype quickly to put in front of the BBC.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby algenon_iii » Wed Oct 12, 2016 12:29 pm

Had a more detailed read of the specs and this really caught my eye
BigEd wrote:
Video display: Either
(a) an integral single line display of 40 characters (each built from at
least 5 by 7 dots) and a modulated UHF output of the full screen (see
below) or
(b) an integral display of the full screen plus a modulated UHF output of
the full screen or
(c) a modulated UHF output of the full screen

A composite video output should be included.

The 'full screen' should consist of at least 24 lines of 40 characters
(*preferably an option of 80 characters from the outset) of upper and lower
case alpha-numerics and (colour) Teletext graphics. These should be capable
of being freely mixed with (colour) medium resolution graphics of at least
200 horizontal points. The medium resolution graphics should be eraseable
separately from the other displays.

The computer should either produce UHF colour signals at the time of
purchase or be easily expaned to produce UHF colour signals. It must be
designed with colour Teletext and colour graphics in mind.

3 John A. Coll


No requirement for RGB monitor output! I've commented before about how an intensity bit could have simply created a better colour palette for the Electron and later Beebs. I'd always assumed that the BBC had specified that there should be an RGB monitor port or at least an option for one and Acorn had chosen a solution that offered best value for money whilst unwittingly shooting themselves in the foot in the process.

In 1981 8 colours was very good https://en.wikipedia.org/wiki/List_of_color_palettes so a simple RGB monitor with no intensity was a perfectly decent solution. However, by the time the electron came out 15 colours was becoming normal (8+intensity), and by the time the B+/Master came out 16 colours was the absolute minimum.

What do you do, require schools to buy a new monitor with their new B+/Master or keep it as is and sell to schools trading on the backward compatibility (software and hardware)? Understandably they chose the later, you don't upset your biggest customer and hit sales (a Cub cost around £250). But in doing so I think they kissed the home computer market goodbye, if someone had £400 to spend on a home computer in 1985/6 they'd buy a "better spec" CPC6128 with a colour monitor.

Hindsight is an amazing thing...

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Commie_User » Wed Oct 12, 2016 12:58 pm

algenon_iii wrote: (a Cub cost around £250).



That's scandalous. Full TVs cost less and while the CUB was good, solid and rich, I've seen much sharper 80s screens.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby paulb » Wed Oct 12, 2016 12:59 pm

algenon_iii wrote:No requirement for RGB monitor output! I've commented before about how an intensity bit could have simply created a better colour palette for the Electron and later Beebs. I'd always assumed that the BBC had specified that there should be an RGB monitor port or at least an option for one and Acorn had chosen a solution that offered best value for money whilst unwittingly shooting themselves in the foot in the process.

In 1981 8 colours was very good https://en.wikipedia.org/wiki/List_of_color_palettes so a simple RGB monitor with no intensity was a perfectly decent solution. However, by the time the electron came out 15 colours was becoming normal (8+intensity), and by the time the B+/Master came out 16 colours was the absolute minimum.

What do you do, require schools to buy a new monitor with their new B+/Master or keep it as is and sell to schools trading on the backward compatibility (software and hardware)? Understandably they chose the later, you don't upset your biggest customer and hit sales (a Cub cost around £250). But in doing so I think they kissed the home computer market goodbye, if someone had £400 to spend on a home computer in 1985/6 they'd buy a "better spec" CPC6128 with a colour monitor.

Hindsight is an amazing thing...


I think the obvious demonstration of learning the lesson is, indeed, the Amstrad CPC and its incorporation of the intensity signal, given that so much of the general design was based on the Beeb. However, what I found interesting was this in the context of Teletext:

BigEd wrote:These should be capable
of being freely mixed with (colour) medium resolution graphics of at least
200 horizontal points. The medium resolution graphics should be eraseable
separately from the other displays.


This seems to read as if the Teletext display could be superimposed on the bitmap display, just like one sees when combining the text with the picture on certain televisions. Although it can obviously be done, I can't imagine that it would have kept the cost or complexity down.

One can also wonder what might have happened had memory been a bit cheaper. Instead of going with the dedicated Teletext hardware, maybe such displays would have been simulated using something like mode 2 instead (like the software-based Jafa Mode 7 product). In other words, a 32K base model might never have had the Teletext circuitry, given that the attraction of supporting Teletext at all may well have been the ability to show Prestel pages or broadcast text pages, not to offer a low memory mostly-text screen mode.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby BigEd » Wed Oct 12, 2016 1:49 pm

paulb wrote:One can also wonder what might have happened had memory been a bit cheaper.

But I think that might the one thing which makes all the difference - computers succeeded or failed depending on how the designers anticipated the future price of memory. It was perhaps the primary driver for what you could or couldn't do. Memory price is such an important variable it's more or less a time machine: double it, and you went back a year or two; halve it, and you go forward a year or two.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby algenon_iii » Wed Oct 12, 2016 3:38 pm

Commie_User wrote:
algenon_iii wrote: (a Cub cost around £250).



That's scandalous. Full TVs cost less and while the CUB was good, solid and rich, I've seen much sharper 80s screens.


Had a quick check in October 86 the std/med/hi res versions were £206/260/420 inc VAT respectively.

I can't remember where they were assembled, I suspect the UK, whereas most TVs by then were probably made in the Far East somewhere.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Commie_User » Wed Oct 12, 2016 4:02 pm

Hmmm. What were the resolutions on those?

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby jgharston » Wed Oct 12, 2016 4:04 pm

paulb wrote:One can also wonder what might have happened had memory been a bit cheaper. Instead of going with the dedicated Teletext hardware, maybe such displays would have been simulated using something like mode 2 instead (like the software-based Jafa Mode 7 product). In other words, a 32K base model might never have had the Teletext circuitry, given that the attraction of supporting Teletext at all may well have been the ability to show Prestel pages or broadcast text pages, not to offer a low memory mostly-text screen mode.

Having an ultra-low-memory full colour display (hardware MODE 7) was one of the huge attractions of the BBC, and its absence a huge failing with the Electron.

I agree regarding the intesity bit. Flash could still have been implemented by changing palette entries on VSync in the same way flash is currently implemented by toggling a bit in the VULA control register. I seem to remember seeing some code somewhere that does exactly this, allowing non-complementary flashing, eg red+yellow instead of red+cyan.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Pernod » Wed Oct 12, 2016 4:05 pm

Commie_User wrote:Hmmm. What were the resolutions on those?

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Commie_User » Wed Oct 12, 2016 4:09 pm

Thanks. That hi-res is just better than the Atari ST's, and in colour I gather.


But that price is still pretty nasty if the brochure's talking about the '90s.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Wed Oct 12, 2016 4:39 pm

algenon_iii wrote:No requirement for RGB monitor output!

Whilst John Coll's specification might not have mentioned it, it was always a requirement of the team who were producing the TV series that the machine should have a 'studio compatible' output that could be fed into the vision mixer. So in practice that would mean a 625-line baseband component output like RGB or YUV.

I've commented before about how an intensity bit could have simply created a better colour palette for the Electron and later Beebs.

You say "simply" but whilst it would probably have been relatively straightforward to add such a bit to the component output, that's not the case for the composite video (PAL-coded) and UHF outputs. The cunning 'TTL' PAL encoder used (which bears a spooky resemblance to a circuit I devised in 1976*) would have needed to be considerably more complicated to generate the correct colour-subcarrier phases and amplitudes necessary to implement those extra eight colours.

Richard.

* I wish I could remember whether I ever gave Acorn a copy of my PAL encoder design. They are almost too similar for it to have been an example of 'two minds thinking alike' but not sufficiently so to be sure the BBC Micro circuit was derived from mine.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Wed Oct 12, 2016 4:53 pm

paulb wrote:One can also wonder what might have happened had memory been a bit cheaper. Instead of going with the dedicated Teletext hardware, maybe such displays would have been simulated using something like mode 2 instead

Having, for my sins, written software-based implementations of the Videotex/Teletext standard (for the 8086 and IA-32 versions of BBC BASIC, plus a standalone Videotex terminal and Teletext editor) I think CPU speed would have been an issue even if there had been enough screen memory. To produce a fast, 100%-compliant, display that way is far from easy.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby BigEd » Wed Oct 12, 2016 4:54 pm

The teletext output is really nice quality too, with rounded characters - difficult to get close to it with a bit-mapped display from those days.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Wed Oct 12, 2016 5:33 pm

Richard Russell wrote:I wish I could remember whether I ever gave Acorn a copy of my PAL encoder design. They are almost too similar for it to have been an example of 'two minds thinking alike' but not sufficiently so to be sure the BBC Micro circuit was derived from mine.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Coeus » Wed Oct 12, 2016 6:30 pm

paulb wrote:
algenon_iii wrote:
BigEd wrote:These should be capable
of being freely mixed with (colour) medium resolution graphics of at least
200 horizontal points. The medium resolution graphics should be eraseable
separately from the other displays.


This seems to read as if the Teletext display could be superimposed on the bitmap display, just like one sees when combining the text with the picture on certain televisions. Although it can obviously be done, I can't imagine that it would have kept the cost or complexity down.


Interesting this was exactly what was done on the RM 380Z. Text and graphics displays were separate with characters from a character generator ROM and bit-mapped graphics overlayed. Also the resolution called for is similar to what I believe the 380Z had so this part of the specification may well have been influenced by the 380Z, quite likely if John Coll was already working in education where the 380Z was already in use.

The description of the monitor ROM also sounds very similar to the RM one.

This all makes the RM decision not to tender even more remarkable. The RM 380Z was an expensive machine, though. Perhaps RM were too much "Rolls Royce" in their approach, i.e. not used to engineering down to a cost as much as Sinclair were too focused on cost rather than engineering up to a specification and what won the contract for Acorn was having the right balance between these two.

Like many, I suppose, I have watched "The Micro Men" and it includes the last minute completion of the Proton prototype. While completing the prototype in a week is remarkable and reflects the skill and dedication of those involved, the more I read the more it becomes apparent they weren't starting from cold.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby IanS » Wed Oct 12, 2016 6:47 pm

Richard Russell wrote:* I wish I could remember whether I ever gave Acorn a copy of my PAL encoder design. They are almost too similar for it to have been an example of 'two minds thinking alike' but not sufficiently so to be sure the BBC Micro circuit was derived from mine.

I thought Steve or Sophie had mentioned in one of their talks that the PAL encoder basically came from the BBC.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby paulb » Wed Oct 12, 2016 10:07 pm

jgharston wrote:
paulb wrote:One can also wonder what might have happened had memory been a bit cheaper. Instead of going with the dedicated Teletext hardware, maybe such displays would have been simulated using something like mode 2 instead (like the software-based Jafa Mode 7 product). In other words, a 32K base model might never have had the Teletext circuitry, given that the attraction of supporting Teletext at all may well have been the ability to show Prestel pages or broadcast text pages, not to offer a low memory mostly-text screen mode.

Having an ultra-low-memory full colour display (hardware MODE 7) was one of the huge attractions of the BBC, and its absence a huge failing with the Electron.


Yes, but that's a consequence of the original Beeb having 16K expandable to 32K and someone probably struggling to see how else they might fulfil the Teletext requirement. What if the Beeb had provided 32K expandable to 64K? Would the BBC really have cared about the Teletext mode requiring 20K or even 15K, especially if the motivation is merely to show Teletext pages, not specifically to offer a low memory mostly-text screen mode?

Mode 7 provided by the hardware - and thus requiring hardly any memory - is just a fortunate outcome of a particular implementation decision. My point is that under different circumstances it might not have been done that way at all, and maybe no-one would have missed it, either.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby daveejhitchins » Thu Oct 13, 2016 6:40 am

algenon_iii wrote:I can't remember where they were assembled, I suspect the UK, whereas most TVs by then were probably made in the Far East somewhere.
They were actually designed and built in Bradford - Microvitec. The finance director, when he'd retired, used to do my accounts :D

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby 1024MAK » Thu Oct 13, 2016 7:14 am

And of course, Microvitec are still alive.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Thu Oct 13, 2016 8:56 am

paulb wrote:Would the BBC really have cared about the Teletext mode requiring 20K or even 15K, especially if the motivation is merely to show Teletext pages, not specifically to offer a low memory mostly-text screen mode?

The BBC would have cared indirectly about requiring a lot of extra memory, yes, because of the cost implications! But even if cost was no object, there are two other important considerations. One is the quality of the displayed text; as has already been pointed out the teletext font is highly legible and the crude 8x8 character set available in the graphics modes would never have been acceptable as a substitute. Secondly, accurate implementation of the full Videotex specification was a requirement, and as I mentioned in another post that would have been difficult, if not impossible, to achieve in software with the CPUs of the day.

It's also instructive to work out just how much memory would have been required for a bit-mapped display capable of reproducing MODE 7 with the same quality and capabilities as the hardware chip. The basic Videotex character cell is typically 8 pixels wide by 10 pixels high, before character rounding; after rounding it is equivalent to 16 x 20 pixels. So with 25 rows of 40 characters that corresponds to 320,000 pixels. If we assume 4 bits per pixel (at least 3 are needed for RGB) that's 160 kbytes, substantially more than the "20K or even 15K" that you mention. Can you imagine the cost and complexity of providing that amount of bit-mapped graphics memory with 1980s technology?

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby paulb » Thu Oct 13, 2016 10:28 am

Richard Russell wrote:
paulb wrote:Would the BBC really have cared about the Teletext mode requiring 20K or even 15K, especially if the motivation is merely to show Teletext pages, not specifically to offer a low memory mostly-text screen mode?

The BBC would have cared indirectly about requiring a lot of extra memory, yes, because of the cost implications!


Right, but this connects with BigEd's comment about memory pricing. Had RAM been more abundant (an aside: I believe that RAM production was what Inmos was originally doing, and so there was a recognised problem at a level intersecting with national strategy), the BBC could have gone with a larger amount purely because it would have offered more capabilities, future-proofing, and so on. If that then got used to provide Teletext in another way, the mechanism involved could have been a distant secondary consideration.

Richard Russell wrote:But even if cost was no object, there are two other important considerations. One is the quality of the displayed text; as has already been pointed out the teletext font is highly legible and the crude 8x8 character set available in the graphics modes would never have been acceptable as a substitute. Secondly, accurate implementation of the full Videotex specification was a requirement, and as I mentioned in another post that would have been difficult, if not impossible, to achieve in software with the CPUs of the day.


I can't comment on Videotex specification issues, and it isn't for me to rule as to whether the 8x8 font would have been acceptable for the BBC's purposes, but I disagree on whether a multicolour mode 4 would have been suitable. No-one really complains about the default font on the Acorn machines.

Richard Russell wrote:It's also instructive to work out just how much memory would have been required for a bit-mapped display capable of reproducing MODE 7 with the same quality and capabilities as the hardware chip. The basic Videotex character cell is typically 8 pixels wide by 10 pixels high, before character rounding; after rounding it is equivalent to 16 x 20 pixels. So with 25 rows of 40 characters that corresponds to 320,000 pixels. If we assume 4 bits per pixel (at least 3 are needed for RGB) that's 160 kbytes, substantially more than the "20K or even 15K" that you mention. Can you imagine the cost and complexity of providing that amount of bit-mapped graphics memory with 1980s technology?


Well, I did a quick calculation for a mode 2 screen of 24 lines which works out at 15K. Of course, that doesn't offer a nice resolution, so you'd have to consider doubling it to offer a mode 1 or 4 screen resolution instead, working out at 30K. Make it 16K or 20K (or 32K or 40K) if you want a slightly nicer font. There would be bandwidth issues, certainly, since the chipset is only delivering 80 bytes per pixel line at most.

Then again, it all depends on how important Teletext capabilities are. I don't recall any of the competing machines offering the same level of Teletext support with the base hardware, and so relatively primitive software emulations (like the Jafa software solution for mode 7 emulation) are deemed acceptable for certain purposes as a result. I guess the BBC wanted to leverage their existing technologies a lot more than the rest of the industry eventually did.

Edit: In the context of the memory needed to provide a Teletext display, it's also worth considering how it was done on the Archimedes, which I seem to remember involved a 40K screen mode (320x256x4bpp). That provided a fairly disappointing visual result - not the same look as on the Beeb - but then the choice of implementation is connected with the vertical resolution supported by the base monitor type. It's worth reviewing those Cub monitors and noting that the 1431 and 1451 support higher vertical resolutions than the 3000 model (released for the A3000), which seems bizarre until one considers that it was probably done to support the interlaced display of the Teletext hardware of the Beeb. So, the method of supporting Teletext appears to have affected the specifications of RGB monitors, possibly deferring the cost of displaying it to that purchase instead.


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