Calling all techies! Fancy doing some unpaid proof reading?

[akeley]

I'm working on a big update for my retro gaming/computing related [urlhttps://archive.org/details/crt-scr-v-0.1_202405]preservation project[/url] at the moment. All the material in it is and always will be freely available, but the upcoming update will also be accompanied by a commercially released digital book. It is meant both as an easily accessible snapshot of the collection and also means of supporting the project for those who might wish to do so.

For the book I need a short, basic description of graphic/video capabilities of every retro system out there. This might sound easy given the wealth of information available online, but as I have just learned is actually an extremely time-consuming minefield, especially given that I'm not technically-minded at all. For that reason I thought I might try and ask for help of the resident experts for whom processing such hardware-related data is second nature.

Since I have some doubts whether this book will top the Amazon bestseller lists (ie will at best sell a handful of copies), I can't offer any financial retribution to the participants. I can only promise my undying gratitude, acknowledgement in the credits, and free copy to those with substantial contributions

**********************************************************
Here's the initial batch:

Atari 8-bit:

DISPLAY: 15kHz, 240p, RF, Composite, S-Video (later models), PAL / NTSC
GRAPHICS: popular modes
-320x192 & 2 colours
-160x192 & 4 colours

PLATFORM: AMSTRAD CPC
DISPLAY: 15kHz, 240p, RGB, RF, dedicated monitors, mostly PAL
GRAPHICS: popular modes
-160×200 & 16 colours,
-320×200 & 4 colours

PLATFORM: Apple II
DISPLAY:15kHz, 240p, Composite, RGB (some models)
GRAPHICS: popular modes
-280x192 & 6 colours (effective 140x192 & 4 colours)
-280x192 & 16 colours

PLATFORM: ATARI ST
DISPLAY: 15kHz, 240p, RF / Composite /RGB (depending on model), dedicated monitors, mostly PAL
GRAPHICS: popular modes
-320×200 & 16 colours

By "popular modes" I mean those which were used in most of the games (not some rare outliers) and perhaps some for productivity, if they were really utilized often.

So, if you spot any mistakes in the above, or feel something really needs to be added please post away! Big thanks in advance...

[AndyC]

256*192*4 is also fairly popular on the CPC, despite not being an "official" resolution, for obvious reasons.

[1024MAK]

The UK TV spec (system I where I is a letter) has a horizontal or line frequency of 15625 Hz. I mention this because the NTSC line rate is 15734 Hz. Hence I don't know if you are just trying to differentiate from the later VGA video standards or what with 15 kHz.

A fair number of the 1970s, 1980s and 1990s home computers use a slightly non-standard arrangement of displaying a progressive (p) scanned image on a TV or monitor that is designed to only display an interlaced (i) picture. They do this by only producing the same field repeatedly (one TV frame on an interlaced picture is made up of two fields, overlapping but vertically offset by one line) and slightly adjusting the video timing to suit. Or by having exactly the same image data in both fields. Some can do one or both of the above, but also true interlaced pictures (e.g. BBC Micro MODE 7, Amiga, plus some others).

Hence personally I would not try to include any p or i as it then gets rather complex or misleading.

The UK 625 line, 15625 Hz, 50 Hz standard for monochrome TV is not technically a PAL signal. PAL is the name of the colour encoding system when colour is added to, or part of a composite video signal or a modulated 'over the air' RF signal. PAL is also not relevant for RGB signals.

The Amstrad CPC range internally produced both a monochrome composite video signal (as used by the Amstrad monochrome monitors) and a variation of an analogue RGB signal (as used by the Amstrad colour monitors and the Amstrad modulator). It is possible to use these machines with various SCART equipped TV's if you buy or make a suitable lead.

There were various models in the Atari ST range. Speaking only about UK models, if a model does not have a RF modulator (and hence a TV output), it will not have a composite video signal in its monitor socket. If it does have a modulator, it will have a composite video signal available. French models differ. All models have RGB outputs. All models are capable of colour low res., colour medium res., and high res. modes. The high res. mode requires either an Atari high resolution monitor or a multisync monitor (the actual function not the brand). Some VGA monitors can be persuaded to also show this mode.

For the colour modes, any analogue RGB monitor could be used. Or TV with a RGB SCART socket.

Most games used low res. or medium res., but some did run in high res. mode.

The following is for the ST, STF, STM and STFM models. Later models increased the number of colour selections available.
320 x 200 pixel, 16 colour palette from 512 selections (low res.)
640 x 200 pixel, 4 colour palette from 512 selections (medium res.)
640 x 400 pixel, monochrome (high res.)

Mark

[akeley]

Thanks a lot for your replies, @AndyC & @1024MAK !

256*192*4 is also fairly popular on the CPC, despite not being an "official" resolution, for obvious reasons.

Thank you. I can include it, I'm just curious how popular do you think it was? Asking because I'd like to feature only the really significant gfx modes, due to lack of space (some machines have heaps of them) and this section is meant to be very brief overall, and hopefully not too confusing to layman such as myself. So, if only a few games/demos used a given resolution then I'd probably skip it, but if it was more significant number then I'd include it (probably settle on including three modes max as a limit)

The UK TV spec (system I where I is a letter) has a horizontal or line frequency of 15625 Hz. I mention this because the NTSC line rate is 15734 Hz. Hence I don't know if you are just trying to differentiate from the later VGA video standards or what with 15 kHz.

A fair number of the 1970s, 1980s and 1990s home computers use a slightly non-standard arrangement of displaying a progressive (p) scanned image on a TV or monitor that is designed to only display an interlaced (i) picture. They do this by only producing the same field repeatedly (one TV frame on an interlaced picture is made up of two fields, overlapping but vertically offset by one line) and slightly adjusting the video timing to suit. Or by having exactly the same image data in both fields. Some can do one or both of the above, but also true interlaced pictures (e.g. BBC Micro MODE 7, Amiga, plus some others).

Hence personally I would not try to include any p or i as it then gets rather complex or misleading.

The point of this very brief (half a column) "tech" section in the book is just to provide a really short, at-a-glance overview of given machine's video capabilities. Therefore I'm using the perhaps not 100% precise terms such as "240p/480i" and "15/31kHz" (also PAL / NTSC). They are widely used nowadays in the CRT and even more general retro fandom, to quickly differentiate between various video systems. But, I do appreciate your feedback and will mull it over....maybe indeed it's better to drop them. I'll probably include links to some more detailed write ups anyway, plus a caveat about the section.

The Amstrad CPC range internally produced both a monochrome composite video signal (as used by the Amstrad monochrome monitors)

Wait, so GT65 displays composite signal? I thought it's also RGB...

320 x 200 pixel, 16 colour palette from 512 selections (low res.)
640 x 200 pixel, 4 colour palette from 512 selections (medium res.)
640 x 400 pixel, monochrome (high res.)

This is similar as with what I was saying to AndyC above- do you think there are enough games using the med and hi resolutions to warrant inclusion?

------------------------------------

Also, some more questions :
-looking at Atari 8 bit modes, they seem weird somehow. What, for example, is the resolution and colours used in games such as Ninja or World Karate Championship (most common "Atari look" I think, at least in later years).

-similar weirdness with Apple II: "280x192 & 6 colours (effective 140x192 & 4 colours) -280x192 & 16 colours" - the same resolution but different number of colours? Or was the first one really just 140x192?

What resolution/colours are eg Karateka or King's Quest

Big thanks again for your input!

[AndyC]

Thank you. I can include it, I'm just curious how popular do you think it was? Asking because I'd like to feature only the really significant gfx modes, due to lack of space (some machines have heaps of them) and this section is meant to be very brief overall, and hopefully not too confusing to layman such as myself. So, if only a few games/demos used a given resolution then I'd probably skip it, but if it was more significant number then I'd include it (probably settle on including three modes max as a limit)

The thing with the Amstrad is the resolution is really just pixel aspect ratio and colour depth, the actual dimensions of the screen are very flexible beyond that (the "official" modes assume 80 columns of high res text).

Shrinking the width to 256 pixels in the 4 colour Mode 1 (where the pixels are almost square) had two advantages: it made the screen the same dimensions as the Spectrum (easier for porting) and it makes each line 64 bytes long rather than 80, which just makes screen maths easier.

So you definitely see a lot of 256 pixel wide 4 colour screens (and 128 pixel wide 16 colour screens slightly less often) but the vertical dimensions might vary (though quick and dirty spectrum ports made 256*192*4 an obvious choice).

[1024MAK]

The point of this very brief (half a column) "tech" section in the book...

Rather than 15kHz/31kHz, maybe TV freq./VGA freq.
Where the computer has a colour TV output, the use of PAL/NTSC is fine. Although note that the French used a third very different colour system. For monochrome, use "625 line/50 Hz" for UK/European. NTSC is fine for monochrome in the USA.

Wait, so GT65 displays composite signal? I thought it's also RGB...

Well, actually its a monochrome monitor that accepts a composite video signal and a separate sync signal. It does not use the RGB colour signals. The CPC computers do output a monochrome composite video signal (including the sync signal). It even says "composite video" in the CPC 464 service manual...
I have a GT65 and have looked at the technical details, as I'm thinking of connecting it to a ZX81...

This is similar as with what I was saying to AndyC above- do you think there are enough games using the med and hi resolutions to warrant inclusion?

For the Atari ST range, it does depend on what you class as enough. I'll provide some links and numbers for you.

Here is a link to a list of 886 games (including educational) on the Atarimania site that run in medium resolution. Medium res. is however mainly adventures and board type games. There are some arcade games though.

For high res., here's a link to a now rather old topic on Atari-Forum listing games that will run in high resolution. And a much larger list (1492) of games (including educational) on the Atarimania site.

Yes, the Atarimania site does list multiple versions for some games.

looking at Atari 8 bit modes

I don't know enough about the Atari 8 bit range to help.

similar weirdness with Apple II

I know even less about the Apple 8 bits...

Mark

[sn3j]

Re Atari ST, there are also many public domain games available that run in high res (b/w) mode.
And perhaps it should be mentioned that the Atari monitor had 70 Hz refresh rate in hi-res which was well received.
So the computer was ideal for gaming and professional use as well.

[akeley]

So you definitely see a lot of 256 pixel wide 4 colour screens (and 128 pixel wide 16 colour screens slightly less often) but the vertical dimensions might vary (though quick and dirty spectrum ports made 256*192*4 an obvious choice).

All right, sounds like it warrants inclusion, maybe with a little note.

Rather than 15kHz/31kHz, maybe TV freq./VGA freq.

But isn't TV freq mostly 15 kHz?

For the Atari ST range, it does depend on what you class as enough. I'll provide some links and numbers for you.

Well, "enough" means some sort of substantial amount, what I mean is not just a few outliers - because there are some more obscure gfx modes across platforms which might've gotten a few games and demos but weren't really popular.

Thank you for the links, seems the medium res mode certainly qualifies, hi res maybe not so much because these games are "compatible" and not exclusive to it. Although sn3j says there were many PD games for that mode, so I guess it does after all.

And perhaps it should be mentioned that the Atari monitor had 70 Hz refresh rate in hi-res which was well received.
So the computer was ideal for gaming and professional use as well.

Yeah, I thought about putting it in my short "description" section because it was a novel thing (at least for the low cost ST offered).

[akeley]

Trying to tackle the next batch, the question is: What were the most popular gfx modes on:
-BBC Micro ( I put "320×256 & 4 colours / 160×256 & 16 colours / MODE 7 (teletext)" in for now)
-Commodore C16
-Commodore VIC
-Commodore 64
-Commodore Amiga

[1024MAK]

For the Acorn BBC B:
MODE 1, 320 x 256, 4 colours,
MODE 2, 160 x 256, 8 colours (the other 8 are flashing effects, making the total 16)
MODE 5, 160 x 256, 4 colours,
MODE 7, teletext, 8 colours.

For BBC A:
MODE 5 and 7

For the Acorn Electron:
MODE 1, 2, 5 and
MODE 6, 40 x 25 text (used for adventure games etc.)

Some games may have used one of the other modes, or used a spit screen (changing mode part way down the display) or used a custom mode. But these were the exception.

Mark

[AndyC]

The C64 mostly use 40*25 character mode, with low-res character cells of 4*8. There are a bunch of wonky restrictions on colours which take too long to explain but you can basically have all 16 colours on screen.

The 40*25 high res character mode (8*8 pixel characters but only two colours per character square) was also used for a fair few things too. There some other modes but they're either less used or harder to distinguish without going into too much detail on colour and pixel restrictions.

[akeley]

The C64 mostly use 40*25 character mode, with low-res character cells of 4*8. There are a bunch of wonky restrictions on colours which take too long to explain but you can basically have all 16 colours on screen.

The 40*25 high res character mode (8*8 pixel characters but only two colours per character square) was also used for a fair few things too. There some other modes but they're either less used or harder to distinguish without going into too much detail on colour and pixel restrictions.

Ok, but how to translate it into the "resolution" format I'm using? Is the following correct?

-160×200 & 16 colours
-320×200 & 4 colours