In the days of 8-bit computers, two of the more common memory configurations were 16K and 64K, implemented as eight RAM chips of 16kbit or 64kbit respectively. The setup was one chip per bit over the data bus, so you couldn't use a pair of 64kbit chips to supply 16K of RAM. (Well, presumably you could if you were willing to let memory access take four times as long, but nobody was.)

For example, when the Commodore 64 was released in 1982, it shipped with 64K of RAM, which was at that time unusual and moderately expensive relative to the previously more common 16K, but became the typical configuration as time went on.

About what year did it get to the point where 64kbit RAM chips didn't cost significantly more than 16kbit so that even if you were aiming at the lowest end of the market, it wouldn't make sense to provide less than 64K?

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    The Electron uses a 4-bit memory bus to reduce chip count, paying for it with slower accesses. So at least one computer went in that direction. Otherwise: some of the very, very early machines use static RAM. Including the Vic-20, if memory serves. So don't factor out that stage in development: one chip with an 8-bit bus, but low density and therefore expensive in another way. – Tommy Jul 29 '17 at 19:18
  • @Tommy True! Okay, think of these as preconditions to my question: assuming you aren't willing to sacrifice access speed, and assuming we are talking about far enough along that 16K of DRAM is the baseline configuration. – rwallace Jul 29 '17 at 19:21
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    @tofro Today, 64kbit RAM chips do not cost four times as much as 16kbit ones! – rwallace Jul 29 '17 at 20:37
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    @tofro And maybe in however many years, 8 GB might be the minimum unit of memory available for sale because anything less isn't worth anyone's while to bother with. So it's a case of when a given quantity of memory gets to that point. – rwallace Jul 29 '17 at 21:43
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    @rwallace well 64kB chips are still available for sale, fortunately (I'm using one in my computer) but 64kB costs about as much as 100MB. – immibis Aug 5 '18 at 22:34

It's reasonable to assume that a 64Kbit DRAM chip would have about the same die size as a 16Kbit DRAM chip, but be made on a more advanced CMOS process with half the feature size. Manufacturing 16Kbit DRAMs on the new process would probably not be economic, and neither would making 64Kbit DRAMs on the old process once the new process existed.

So, at some point shortly after the introduction of that new CMOS process, the two chips would be about the same size and therefore price. Furthermore, computers would then be able to use fewer chips to support useful RAM sizes, permitting a reduction in the size (and thus cost) of their PCBs.

As a data point, the difference in price between the BBC Micro Model A (16KB) and B (32KB) was £100 in 1982, when 16Kbit DRAM chips were standard. The RAM quantity wasn't the only difference between these models, but it must have contributed significantly. Let's be conservative and say it was £4 per KB.

In 1984, the February edition of Acorn User featured a 16KB "Sideways RAM" expansion board, using 16Kbit DRAM chips, for £35, while the July edition featured a 128KB model (from the same manufacturer!) using 64Kbit DRAM chips, for £40.

That's a reduction from about £2 per KB to £0.30 per KB within 5 months, and the time requested by the OP must lie within that range.

  • Would 5-volt only 16K chips have used the older process, or would 16K chips have gone to a higher-resolution die die when they lost the need for a negative supply? – supercat Oct 5 '18 at 22:44
  • @supercat The BBC Micro used the HM4816A-3 DRAM chips, which are 16Kbit and use a single supply. This was several years before the 64Kbit chips arrived. – Chromatix Oct 7 '18 at 0:31

At a very rough estimate, around the beginning of 1984. Amstrad introduced the CPC 464 in spring 1984 with 64 K, and announced the CPC6128 for the US market very shortly thereafter.

(source: You’re NOT fired: The story of Amstrad’s amazing CPC 464 • The Register)

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    I don't think that answer fits - The CPC464 and the CPC6128 are two generations of a computer. I think the question was not "when was the first time RAM prices fell so fast that two generations of the same computer could meet in the shops. It's more like "component prices same day". – tofro Jul 29 '17 at 20:11
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    Fair comment. My answer was really as a bookend date to indicated that DRAM prices were low by mid-1984. No matter what Commodore was thinking when they brought out the C16 … – scruss Jul 30 '17 at 22:13
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    I'd say 1983 was approximately the point where it became cheaper to manufacture a new computer with 64k instead of 48k (because you could do 64k with 8 64k chips, but 48k would have required 16 chips... 8 32k chips, and 8 16k chips). I think there was one 8-bit computer that actually SHIPPED with 64k on-board, but could only USE 48k of it due to a last-minute manufacturing hack that allowed them to use cheaper chips without bothering to make the extra ram usable. – Bitbang3r Jul 31 '17 at 21:30
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    there were also the Spanish computers shipped with 8 K of non-functioning RAM, as there was a special tax on computers with ≤ 64 K. – scruss Jul 31 '17 at 23:31
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    @Bitbang3r - at least at retail prices, there was still a huge variation in cost between 16 and 64K chips (one retailer whose advert is online charged 80p for 4116s and £4.50 for 4164s, for example) in mid 1983. And the hack you're thinking of is probably the Spectrum, which used a trick approximately on the lines you're thinking of: the base board was 16K and was increased to 48K by the use of adding 64K chips that had been sold cheap as rejects because there was a single bit error on one half. – Jules Aug 26 '17 at 10:18

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