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Hey guys, I actually stopped by this article hoping to find out whether or not FPM and/or EDO Simms are backward-compatible with the older type my shiny new 486DX wants, but the article doesn't say one way or the other! Could someone in the know clarify this point in the article? Thanks.Mfrisk (talk)05:25, 24 February 2010 (UTC)[reply]

FPM is/was pretty much the standard type of DRAM used on 30-pin or PS/2 SIMMs. EDOs are compatible with most older chipsets not actively supporting them, but some simply won't work. --Zac67 (talk)22:08, 25 February 2010 (UTC)[reply]

486? If in doubt, stick with FPM. A DX4 or Evergreen overdrive might see some benefit from EDO if the motherboard supports it, particularly a 120~160Mhz overclock, but you probably won't see any meaningful speedup on a 66 or below. The bus itself is just too slow, and the CPU isn't multipliered high enough to make serial requests fast enough to oversaturate the RAM. Plus, it's way more compatible - you can run a Pentium off FPM if you have to, but older machines can be picky about EDO.193.63.174.211 (talk)19:06, 9 May 2012 (UTC)[reply]

It's different memory technologies. And no, they are NOT compatible. Lightbulbs are excellent analogy, they use the same socket all over the world (E14, E27 being the most common), but they will not work all over the world because the current is different... (110v in US, 230v in EU for example). Now, your motherboard MAY support both. But without more info it is impossible to say.— Precedingunsigned comment added by213.65.244.152 (talk)00:56, 30 June 2016 (UTC)[reply]

FPM and EDO are not that different. Micron had an article on this.Yuhong (talk)01:30, 22 January 2017 (UTC)[reply]

I've rewritten the introduction bit, because it seemed to tell this:

- 286 systems used SIPPs

- 386+ used SIMMs

Now I've seen loads of 286 systems, but I've never seen any with SIPP modules. They all used SIMMs, or in a few rare cases, bare DIPs. That's why I've changed it to:

- 8088 systems used DIPs

- 286+ mostly used SIMMs

Though I find it hard to prove this. It'd be nice if someone could find a credible source to verify it :-)Robin F.22:55, 11 March 2006 (UTC)[reply]

Anecdotally: I've only taken one 286 apart... a 1987, fairly standard office-work model. It had SIMM sockets (two of 'em, compatible only with 256kb modules), backing up its 640kb of soldered-in-place DIPs (for a rip-roaring total of 1.125MB). SIPs must have crashed and burned pretty hard. Not even Atari bothered with them, fer chrissakes...193.63.174.211 (talk)18:58, 9 May 2012 (UTC)[reply]

Atari DID use SIPs in one model (STacy or STBook). And yes, SIP are rare.

And no, you can not make a cutoff at 8088. Simms took the industry by storm, beginning during the 286 era. Early 286 still used DIP, sometime mid to late 80's, anything without SIMM was basically unheard of.— Precedingunsigned comment added by213.65.244.152 (talk)01:01, 30 June 2016 (UTC)[reply]

I believe that it was the 1988 DRAM shortage that made SIPPs popular (especially when 256Kx4 DRAM reached crossover with 256Kx1), which was replaced by SIMMs not long afterwards.Yuhong (talk)01:40, 22 January 2017 (UTC)[reply]

It would be nice if the size range (megabytes/megabits) would be included.

Also, pinouts seem like an obvious must-have.

2006-08-19 17:02

Did such monster-sized SIMMs really exist? 128MB seems too large for a 72-pin SIMM. In terms of cost per megabyte, computer RAM was very expensive a decade ago. So 128MB 72-pin SIMM would have been prohibitively expensive to produce!Hellcat fighter12:57, 6 October 2007 (UTC)[reply]

You're making the rookie mistake of considering only home users, and not the server market. Where I work, we have some servers with 96GB onboard, using (for the time being) very-high-capacity 16GB DIMMs. They look just like regular ones... except their chips are extremely high density and therefore cost an absolute bomb. We couldn't afford the 32GB ones to max the machines out at 192GB... After all you could make the same argument about 16MB 30-pin SIMMs. By the time their star was fading, 8MB onboard was still the mark of a fairly snazzy computer - probably a couple of 4MB 72-pins - and most people settled for 4MB or even 2MB, formed from rows of 1MB modules. But you can bet there were some heavyweight 64+ MB servers out there which would have made use of them. It's the same market for which seemingly low-capacity, 15000rpm HDDs (and 500,000 IOP SSDs) are made for.193.63.174.211 (talk)19:02, 9 May 2012 (UTC)[reply]

Actually the JEDEC standard (look at the Google Cache for a file named 4_04_02R8.PDF) specifies even larger SIMMs with up to 2 gigabytes (512M x 36) of memory and 14 address lines (A0 to A13). Thus I think the section needs to be updated to reflect that fact...— Precedingunsigned comment added by109.193.3.251 (talk)21:14, 2 February 2014 (UTC)[reply]

128mb 72-pin SIMMs existed. I've personally installed some in servers my current employer had. The cost was ... extreme. Just the hardware of each server was in excess of 50k+ USD at the time.— Precedingunsigned comment added by213.65.244.152 (talk)01:27, 30 June 2016 (UTC)[reply]

That being said, I believe that EDO 168-pin DIMMs was more popular for 64Mbit DRAM chips, especially because it was easier to support ECC using them.Yuhong (talk)01:41, 22 January 2017 (UTC)[reply]

In the Pinout table "Presence Detect 1" is listed twice. It appears that one of the two should have been "Presence Detect 5". Also pin #8 is listed twice. One pin 8 should be 48. There may be other issues. Here is another referance that might be helpful...

http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=pinconmem_simm_ecc_72pin

Oct 23, 2006

http://www.ll.georgetown.edu/federal/judicial/fed/opinions/95opinions/95-1276.html

It lists the history of the invention of the SIMM module. An employee who entered Wang in 1982 eventually invented it.—Precedingunsigned comment added byJWhiteheadcc (talk •contribs)01:43, 15 March 2010 (UTC)[reply]

...why were the 30-pin SIMMs only available in powers-of-4 sizes, rather than powers-of-2? It led to some rather odd situations, like a 4-row, 16-bit computer only allowing sizes of 0.5, 1.0, 2.0, 2.5 and 4.0 (with, say, a typical upgrade being to add two 1mb modules to an existing pair of 256kbs, despite it being quite a bit more costly and not masses more useful than upgrading to 1.5 would have been, though it was still better than only going up to 1.0) ...

Was there some actual technical reason that 512k, 2mb, 8mb modules never appeared, or was it just a strange convention that ended up sticking? Obviously whatever it was never affected 72-pin ones, as I've happily mixed 16, 8 AND 4mb modules simultaneously in the same PC before (16 + 8 + 4 + 4 = 32 :)

And did anyone ever seriously use 1 and 2mb 72-pins? I don't know if I've ever even seen them, not even on eBay.193.63.174.211 (talk)19:11, 9 May 2012 (UTC)[reply]

Take a look at the pinout: the DRAM address bus is multiplexed, so an additional line yields two additional address bits, hence 4x the size. Non-rectangular DRAM chips (mainstream) started only with SDRAM. For e.g. a 2 MB SIMM you'd need two banks of 1 MB each which isn't possible with 30-pin (but with PS/2). Mixing different RAM module sizes (=chip densities) depends on the RAM controller in use, some have several limitations. And yes, I've even got some 2 MB PS/2 SIMMs (and 64K 30-pins) somewhere, but when that form factor became popular nobody wanted them any more.Zac67 (talk)19:51, 9 May 2012 (UTC)[reply]

This reminds me of Mac 2MB SIMMs with PALs. My guess is that the PALs are used to emulate non-rectangular DRAM ranks with two ranks of rectangular DRAM. AFAIK 4Mx16s was already available only with 12 by 10 DRAM addressing, which was popular in laptops. The first PS/2 machine to use 72-pin SIMMs was the PS/2 model 80 in 1987 I think. -Yuhong (talk)01:55, 22 January 2017 (UTC)[reply]

Yes, odd sizes existed, but afaik the only hardware I ever came across using these 512k or 2mb SIMM modules were printers.8 MB 72 pin simms were pretty common though. They were grouped with 2mb, 32mb and 128mb SIMMs as "double sided", basically appearing to the memory controller as 2 simms half the size. It needed special support in hardware, "stole" one memory slot and often required specific support for the memory type.— Precedingunsigned comment added by213.65.244.152 (talk)01:08, 30 June 2016 (UTC)[reply]

"DRAM technologies used in SIMMs include FPM (Fast Page Mode memory, used in all 30-pin and early 72-pin modules), and the higher-performance EDO DRAM (used in later 72-pin modules)."Why does wikipedia state this with authority? I know for a fact 30 pin SIMMs were available in EDO versions aswell as SRAM variants and other types. Now, MOST were FPM, I can grant you that, but considering the authority wikipedia got whoever wrote that sentence know shit about 80's/90's computing and should be banned from these kind of articles...

It probably makes more sense to talk about DRAM chips not SIMMs. Now, EDO x1 chips was probably uncommon. Often 30-bit SIMMs used two x4s plus an x1 for parity.Yuhong (talk)01:35, 22 January 2017 (UTC)[reply]

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