VOGONS


First post, by Half-Saint

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As the title says.. how to tell, if a module is EDO or FPM?

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Reply 1 of 14, by stbunny

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IMO, there's only one way - read datasheets.

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Reply 3 of 14, by BastlerMike

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I worked out that there seems to exist a general rule in the partnumbering which is suitable for many memory manufacturers.
Have a look at the numeric part of the partnumber. If it ends with a "0" then you have FPM memory, if it ends with something like 3, 4, 5, 7 or 9 then you have most likely EDO memory.

Left one -> EDO, right one -> FPM

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Reply 5 of 14, by Jepael

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No. NEC is FPM because datasheet says so, and the part number 4216400 also ends with zero. TI is EDO because datasheet says so, and the part number TMS417409DJ ends with 9.

Reply 7 of 14, by Malik

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There is another method - visibly, the chips on FPM sticks are narrower (when you see them longitudinally) than the EDO counterparts (EDO chips are slightly more broad). Not very reliable, but at a quick glance may help.

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Reply 8 of 14, by dca2

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BastlerMike wrote:

Have a look at the numeric part of the partnumber. If it ends with a "0" then you have FPM memory, if it ends with something like 3, 4, 5, 7 or 9 then you have most likely EDO memory.

Me too -- I applied this trick every time in a recycle store and identified EDO or FPM SIMMs without single mistake by far 😈 .

Reply 9 of 14, by Teti

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I hope it helps, I have quite a database of SIMM modules here:

http://martenelectric.cz/simm-sipp-ram-chip-database.html

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Vintage audio gear connoisseur, computer enthusiast, time-nut, music lover, vintage games gamer, nerd, tinkerer and shady electronic projects maker

Reply 11 of 14, by pentiumspeed

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Don't assume, the FPM came in 60ns and rarely 50ns.

I have several FPM SIMMs in 60ns rating.

Cheers,

Great Northern aka Canada.

Reply 12 of 14, by mkarcher

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Matth79 wrote on 2022-01-09, 20:23:

Of the most common modules, -70 is likely to be FPM and -60 is likely to be EDO
There may well be FPM chips that are faster then 70nS (but rare), and pretty sure EDO was never in 70nS specification

I have a lot of 60ns FPM memory. I estimate the FPM-to-EDO ratio of 60ns PS/2 SIMMs is around 50:50 in what I have at hand. On the other hand, I don't think I have any 70ns EDO SIMMs (at least at capacities above 4MB), so that part of the rule of thumb might work quite well.

Another rule of thumb: If you have SIMMs made by IBM or COMPAQ, chances are quite high that they are EDO - they had custom mainboards that were early EDO adopters while the mainstream was still using FPM.

In my experience, the best way to find out whether a module is EDO or FPM is just typing the chip model number into a search engine (like Google), and see what comes up in the results.

Reply 13 of 14, by pentiumspeed

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IBM and Compaq used FPM SIMMs in 72 pin lot on consumer and servers during late 386 and mostly 486 and early Pentium era.

Besides, most of the PS/2 line starting with 386sx and 386, 486 and Pentium used 72 pin SIMMs of their design and is not standard. Not all of IBM made DIMMs is not compatible with clones because their IBM SIMMs used one CAS and one RAS as opposed to standard four CAS lines due to all same 4bit x 9 chips design. The industry standard 72 pins with parity used four CAS lines means requires four 1 bit dram ICs for parity or one quad CAS with four parity outputs (not 4 bits) in one IC which is different from one CAS per IC (tied together on either 4 bits or 8 bits ICs to form 32 bits datapath.

By the way, on PS/2 And only a exception is PS/2 286 used one 72 pin slot board is model 50Z.

Compaq and non-IBM computers using 72 pin SIMM adheres to industry standard SIMMs. The late IBM-made computers that are not PS/2 also used industry standard 72pin SIMMs.

Cheers,

Great Northern aka Canada.

Reply 14 of 14, by Anonymous Coward

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If you have a lot of SIMMs to test, there are SIMM testers that can tell you. They're expensive though.

Just read the datasheet. It's not that hard.

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