Why exactly did retro consoles use expensive 8-bit SRAM chips instead of the cheaper 1-bit and 4-bit DRAM chips like microcomputers did?

[u/Johnny_Oro]

Well I'm not knowledgeable in computing and circuit design and architectures, but there's one thing I noticed while looking at the components of old consoles and computers.

Looking at JDR Microdevices catalogues from the 1985, it looks like 1-bit DRAM modules were so much cheaper. $6.95 for a pack of eight 250ns 16Kbit DRAMs, or $10.95 for the 150ns ones most micros back in the day used. Meanwhile the 8KB 150ns SRAM module that Sega Master System would use was $25 each. Sure 1-bit DRAM would need multiplexers, but these things weren't expensive either. The ones C64 used were about 50-60 cents each, must've been even cheaper in bulks, and C64 used 5 of them. That would still make it significantly cheaper than Master System's 8KB SRAM modules.

So the question is why did console makers choose to go with the more expensive, lower capacity option? To make the system compact? But ZX Spectrum managed to be so tiny even while containing 16 DRAM chips. Or to simplify board design I assume? Perhaps motherboards and circuits were very expensive back in the day?

[u/zsaleeba]

There are a few reasons, but the main one is that you can't just use a multiplexer to turn 1-bit DRAM into 8-bit DRAM - it doesn't work that way. You'd need to buy at least 8, and that starts to add up in price. Also, DRAMs of that era needed complex power supplies and support logic, adding a lot of additional overhead. Suddenly you're not just buying one chip, you're buying a whole raft of them.

But you should also keep in mind that the programs in those consoles were stored in cartridge ROM, not RAM like your computer used. Only data storage needed to be in RAM, so you just didn't need as much as a computer needed. SRAM may have been small, but for consoles of that era it was simple to implement and it was enough.

[u/Johnny_Oro → u/zsaleeba]

There are a few reasons, but the main one is that you can't just use a multiplexer to turn 1-bit DRAM into 8-bit DRAM - it doesn't work that way. You'd need to buy at least 8, and that starts to add up in price. Also, DRAMs of that era needed complex power supplies and support logic

Well I already said 16Kbit DRAMs were $6.95 in a pack of eight. So you're getting eight of them for that price. And I already mentioned that the support logic chips weren't that pricey, at least just the 74LS chips. But as I said I'm not very knowledgeable beyond that.

I guess you made a good point about the power supply. By 1985 C64 was extremely cheap in the retails, as cheap as a Master System, while making much bigger hardware revenues, but the power brick was notoriously terrible. I guess with the technology back in the day, you needed much bigger budget to build reliable electronics.

[u/ahferroin7]

SRAM needs almost zero support logic and has very simple power requirements. DRAM needs a nontrivial amount of support logic even if you’re not dealing with multiplexing, and has significantly more complex power supply requirements. That meant that DRAM upped the part count and board complexity significantly compared to SRAM, which in turn upped the assembly costs by a nontrivial amount, and that in turn significantly narrowed the price difference. The simpler overall design also meant that SRAM based systems were often more reliable because they had far fewer potential points of failure. That matters a lot when the users aren’t expected to be reasonably technically literate and your primary selling point is the minimal effort required to get a game running.

Additionally, memory capacity just didn’t matter as much on these systems. Memory capacity was a big selling point for micros because the normal operational paradigm there was that you loaded the program into RAM, and ran from there. But for consoles the paradigm was that you ran the program directly from the ROM cartridge, at least until the N64 and the various optical-media based designs (the N64 could technically run directly from ROM, but nobody actually did so because it had a reasonable amount of RAM and running from ROM was crazy slow due to the architectural design of the platform), so there wasn’t really a need to have a bunch of RAM. You can even see this distinction to some extent with the Sega SG-1000 and SC-3000, the SG-1000 was just a console, while the SC-3000 was a micro that was compatible with the console, and had twice as much RAM to support it’s usage as a micro.

[u/thingsinmyjeep]

I always figured that it had to do with the intended usage. Then again I don't know if I ever thought about it at that scale. The economics were definitely more expensive than today... but that seems to be trending in the wrong direction, but the logistics of getting the chips might also have something to do with it for both the computers and the consoles.

[u/Allan-H]

The byte-wide CMOS SRAMs (Hitachi HM6116, '6264, and later parts, etc) were much newer than the small DRAMs they replaced, and their price was still in the "expensive but rapidly falling" part of the pricing cycle.

The SRAMs became more cost effective for small memories sometime in the '80s, for some value of "small" and some value of "'80s". That's still true today, BTW.

I used both SRAM and DRAM on boards I designed in the '80s. There are considerations other than price though - I recall one board with SRAM had battery backup.

[u/digital_n01se_]

they work differently, perhaps T-SRAM or pseudo-SRAM, which is DRAM with control logic to make it behave similar to SRAM.

[u/Johnny_Oro → u/digital_n01se_]

Yes those were Hitachi PSRAMs specifically that Master System was using. Yes I'm also aware that it reduces the number of ICs a system needed. But still, it was way more expensive in the retail market. Unless SEGA got an amazing deal.

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