CD-ROM2 memory

[Blammo]

I've never seen any suggestion that the original CD expansion contained any extra RAM over the base console (8k work + 64k video). How on earth did it manage with such a tiny amount of space to work in? Is 72k enough for a level of a typical game, plus al graphical and sound assets? 

[ccovell]

The PCE-CD expansion has 130k extra RAM built-in: 64K for game code, 64K for ADPCM sample data, and 2K backup memory.  But yeah, 64K wasn't much for a complete game to run in.  It was just enough for a level or two with good programming.

[Blammo]

I see. Makes more sense. Strange I've never heard about it before. Everyone probably gets their facts from Wikipedia - speaking of which, they claim that the super system card adds 192K, taking the total up to (apparently) 256K. Yet the base unit has 72k total, which would make the total amount 264K. Wat??

Perhaps the extra went entirely on graphics, and they weren't counting work RAM at all in those figures... in which case, how do they maintain compatibility with the CDROM2, with its 64K for ADPCM? Was the other 64K in the CDROM2 for CPU or graphics?

And according to the same page the Duo had a single 256K DRAM... is that possible, given the separation between main and video memory (also, admittedly, something I got off Wikipedia). Something on that website needs a bit of clarification, I think. Either that or I'm failing to understand something. =|

[nat]

The TG-16 page on Wikipedia is a fucking mess, to put it nicely. It.... needs a lot of work. Has for a long time.

[ccovell]

...claim that the super system card adds 192K, taking the total up to (apparently) 256K. Yet the base unit has 72k total, which would make the total amount 264K. Wat??...

And according to the same page the Duo had a single 256K DRAM... is that possible, given the separation between main and video memory (also, admittedly, something I got off Wikipedia). Something on that website needs a bit of clarification, I think. Either that or I'm failing to understand something. =|

You are kind of doing both.  The PCE core unit has 8K of work RAM and 64K video RAM.  The CD-unit adds 64 more K of work RAM, 2K of backup RAM, and 64K ADPCM RAM.  Probably Wikipedia is taking the base Core specs as a given, and focusing on whatever is added by the CD unit.  The Duo likely had a 256K DRAM just for the CD system RAM, and probably somewhere else on the board is the 2K backup RAM, 64K ADPCM RAM, and 8K PCE work RAM in their own separate chips.  Wikipedia probably doesn't mention all this for reasons of scope.

[guyjin]

The TG-16 page on Wikipedia is a fucking mess, to put it nicely. It.... needs a lot of work. Has for a long time.

Should we get together and make it a group renovation project?

Do you have something citeable for those stats, Chris?

[esteban]

The TG-16 page on Wikipedia is a fucking mess, to put it nicely. It.... needs a lot of work. Has for a long time.

Should we get together and make it a group renovation project?

Do you have something citeable for those stats, Chris?

It would be nice if we worked together to improve the quality of Wikipedia pages on TG-16/PCE etc.

I can't help much concerning the technical specs, but I'd love to contribute to other areas.

TANGENT: A few years ago, some idiot(s) kept overstating the significance of the Johnny Turbo advertising campaign in the TG-16 article (going so far as to claim that JT was the official mascot of TTi. Ha!). I had fun editing the article to reduce the overly-sensational attention placed on Johnny Turbo and clarify the official mascots of TG-16 and TurboDuo.

I haven't looked at the article in years, though. I cringe at what I might find...

[FraGMarE]

I can't help much concerning the technical specs, but I'd love to contribute to other areas.

The 'Technical Specifications' part of the Wikipedia article is actually correct and factual (albeit probably a bit too verbose).  I edited and corrected that specific portion of the Wikipedia article a few years back and I've been watching it like a hawk ever since (to make sure nobody adds erroneous info).

[Blammo]

So how do you explain the bit about the Super System Card's memory not adding up? If it's correct, it's quite ambiguous and hard to fathom.

(Core unit has 8 + 64k = 72k.
Super system card has 192k. 8 + 64 + 192 = 264k.
Duo has 256k - what happened to the other 8k? Is it included in the 256K or not, or maybe it wasn't even used in CD games at all - I can't tell from the article. And what happened to the 64K of audio sample RAM? Was that included in the 192K, or is it totally separate, or was it in the CD system instead of the card, or... etc...)

And, upon re-reading the article, it appears that the Super System Card also has access to all the extra RAM from the original CD-ROM2 system, because the RAM was in the CD player and/or the interface rather than on the card. So there's an even bigger discrepancy between the 192K and the 256K.

[spenoza]

I think when discussing system card memory, the specifications are talking basically about the ROM-substitute DRAM storage. Thus the 8k CPU RAM, the 64k VRAM, and the 64k ADPCM RAM are not taken into consideration, because they are fixed-purpose RAM spaces. The RAM being talked about for the system cards is basically CD-ROM data cache, meant to emulate/serve the same purpose as the ROM data of a HuCard.

So in that sense, the CD-ROM attachment adds 64k data cache. The SuperCD card adds 192k to that for a total of 256k of data cache. Similarly for the Arcade Card Duo/Pro. Thus it would make sense that the Duo has a single 256k data cache. It also has other little caches of single-purpose RAM.

This is what I get from reading the various technical specs. If this is correct, it does mean the dedicated TurboDuo article on WP is incorrect (stating the system had 64k VRAM + 192k SuperCD RAM, instead of 64K VRAM and 256k of data cache RAM).

[ccovell]

Here is a simplified block diagram of the PCE, PCE+CD, and Duo memory arrangement.  The physical arrangement of chips (and chip count) doesn't matter as much as the logical arrangement and how it is accessed.

Let me know if you find any major errors.

[spenoza]

That is pretty much the way I understand it, though is it safe to call the CD and Super CD data caches work RAM? Are they identical to the 8k main RAM that the CPU has access to? Because if they are basically REAL system main RAM expansions, I can see why HuCards have trouble keeping up with later CD titles.

[FraGMarE]

So how do you explain the bit about the Super System Card's memory not adding up? If it's correct, it's quite ambiguous and hard to fathom.

It's not talking about the 8KB of work RAM in the PC-Engine base unit itself.  It's strictly talking about the CD work RAM for loading data directly off the CD (which does indeed add up to 64KB or 256KB for the CD-ROM2 and Super CD-ROM2 respectively).  The 8KB of work RAM in the base unit could potentially be utilized for this purpose, and so could the 64KB of ADPCM RAM for that matter, but that was not their intended purpose.  Please see, ccovell's diagram... it'll give you a pretty good idea of how the whole thing was arranged, in terms of RAM.

Here is a simplified block diagram of the PCE, PCE+CD, and Duo memory arrangement.  The physical arrangement of chips (and chip count) doesn't matter as much as the logical arrangement and how it is accessed.
Let me know if you find any major errors.

You might as well include the 32x6 bytes of truncated RAM used by the PSG sound channels for the sake of being all-inclusive.

[ccovell]

You might as well include the 32x6 bytes of truncated RAM used by the PSG sound channels for the sake of being all-inclusive.

Not my intention.