VOGONS


FPM or EDO

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First post, by eesz34

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I've acquired a 386DX motherboard that uses Opti 82C495/82C206 chipset with eight 30 pin SIMM slots. I don't have it in my possession yet, but I want to order SIMMs now so I don't have to wait. Unfortunately this particular model isn't on TRW.

I think it's safe to say I'd need four or eight SIMMs at a time. Would it most likely expect FPM? I've read how EDO is backwards compatible in an FPM system, but I don't trust that because EDO did not work in my Compaq 386. Does FPM work in a system compatible with EDO?

What is the safe type to buy ahead of time? (because I'm impatient)

Reply 1 of 22, by Disruptor

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There do exist 30 pin SIMMs with FPM.
There do exist 72 pin SIMMs with FPM.
There do exist 72 pin SIMMs with EDO.
There do NOT exist 30 pin SIMMs with EDO.

What size of Cache does your motherboard have?
If it is too few, I recommend you to buy 8 FPM 30 pin SIMMs with 1 MB.
Otherwise, 4 FPM 30 pin SIMMs with 4 MB.

Access time should be 70 ns or perhaps 60 ns on a 40 MHz system.

Reply 2 of 22, by eesz34

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Disruptor wrote on 2024-06-02, 14:36:
There do exist 30 pin SIMMs with FPM. There do exist 72 pin SIMMs with FPM. There do exist 72 pin SIMMs with EDO. There do NOT e […]
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There do exist 30 pin SIMMs with FPM.
There do exist 72 pin SIMMs with FPM.
There do exist 72 pin SIMMs with EDO.
There do NOT exist 30 pin SIMMs with EDO.

What size of Cache does your motherboard have?
If it is too few, I recommend you to buy 8 FPM 30 pin SIMMs with 1 MB.
Otherwise, 4 FPM 30 pin SIMMs with 4 MB.

Access time should be 70 ns or perhaps 60 ns on a 40 MHz system.

I saw a post from someone on Vogons (could have been you for all I remember) that also said there's no EDO 30 pin SIMMs. But someone on eBay sells them! However they appear to be new assemblies. Wonder what people buy them for? I accidentally bought those for a 386 and of course it didn't work. Anyway, that makes it easier if I should be avoiding EDO.

I think it's 256K cache. So you're saying having more SIMMs allows better performance because of interleaving?

Thank you for your suggestions. I know what to get now.

Reply 4 of 22, by jakethompson1

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eesz34 wrote on 2024-06-02, 15:01:

I saw a post from someone on Vogons (could have been you for all I remember) that also said there's no EDO 30 pin SIMMs. But someone on eBay sells them! However they appear to be new assemblies. Wonder what people buy them for? I accidentally bought those for a 386 and of course it didn't work. Anyway, that makes it easier if I should be avoiding EDO.

I think it's 256K cache. So you're saying having more SIMMs allows better performance because of interleaving?

Thank you for your suggestions. I know what to get now.

The issue is you don't want more RAM than your board can cache. 4 MB SIMMs would have been extremely expensive when 386 systems were current, and 16 MB is a lot of memory for a 386. Nonetheless, if you do have 256 KB cache (or even 128 KB) you should be able to cache all of that.

In the highly unlikely event that you would want to use an ISA SVGA card with a linear framebuffer (some discussion here: https://www.xfree86.org/3.3.6/cirrus5.html#5), you might want to stick with 8 MB RAM, since 16 MB would overlap with the card's framebuffer. Most 386 systems would've come with 4 MB, so 8 MB is plenty IMO.

Reply 5 of 22, by The Serpent Rider

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4 Mb was pretty standard when AMD finally released their 386 clones.

I must be some kind of standard: the anonymous gangbanger of the 21st century.

Reply 6 of 22, by mkarcher

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eesz34 wrote on 2024-06-02, 15:01:
Disruptor wrote on 2024-06-02, 14:36:

There do NOT exist 30 pin SIMMs with EDO.

I saw a post from someone on Vogons (could have been you for all I remember) that also said there's no EDO 30 pin SIMMs. But someone on eBay sells them! However they appear to be new assemblies.

This could also have been me. I vaguely remember to have claimed that, and got corrected, but couldn't find my claim easily. However, I could find two threads talking about the availability of 30-pin SIMMs, one of the showing a photo of Keystron branded 30-pin EDO SIMMs and another one just hinting to the existence of such modules on ebay and another poster mentioning that the Keystron modules seem to be modern assemblies, just as you said.

So while "there are no 30-pin EDO SIMMs" likely was true in 1996, there seem to be that many newly made 30-pin EDO SIMMs in circulation right now that this statement needs to be wiped from collective memory because it is outdated in 2024.

Reply 7 of 22, by dionb

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mkarcher wrote on 2024-06-02, 19:15:

[...]

This could also have been me. I vaguely remember to have claimed that, and got corrected, but couldn't find my claim easily. However, I could find two threads talking about the availability of 30-pin SIMMs, one of the showing a photo of Keystron branded 30-pin EDO SIMMs and another one just hinting to the existence of such modules on ebay and another poster mentioning that the Keystron modules seem to be modern assemblies, just as you said.

So while "there are no 30-pin EDO SIMMs" likely was true in 1996, there seem to be that many newly made 30-pin EDO SIMMs in circulation right now that this statement needs to be wiped from collective memory because it is outdated in 2024.

I call bs on that.

Just looked up "30 pin EDO SIMM" on eBay and got a pile of hits.

But...

The first five that had legible chip codes showed:
"16MB 30pin SIMM RAM MEMORY 60ns EDO with non-Parirty 16x8 30p" HYB514100 4M x 1-Bit Dynamic RAM with Fast Page Mode
"16MB 30pin RAM MEMORY SIMM 60ns EDO with Parirty 16x9 30p" HYB511740 4M x 4 Bit 2k 5 V 50 ns FPM DRAM
"4MB 30pin EDO SIMM RAM MEMORY with parity 4x9 30-pin" HY5116100 16Mx1, FPM
"Siemens 1MB Sim 30-PIN 70ns GT-3009 EDO Memory" KM44C1610 16M x 4bit CMOS Dynamic RAM with Fast Page Mode. Also note that Goldstar GT-3009 is listed in a lot of other places and no one else claims that it's EDO.
"Texas Instruments TMS417400ADJ-60 1 6MB Simm 30-pin 60 ns 3-Chips Edo Ram" - yeah, the TMS417400ADJ is 4Mx4 DRAM, not a mention of EDO in the datasheet.

So despite SIMMs being labeled "EDO", the chips are clearly FP.

Sounds to me like some idiots (mainly, but not exclusively, at Keystron) thinking "DIMM=SDRAM, SIMM=EDO" and selling modules on that basis.

Reply 8 of 22, by kingcake

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If 30-pin EDO SIMMS existed, they weren't for standard PC motherboards. I could see them existing for expansion cards that required RAM or embedded systems.

This is an interesting case, because the Opti 82C495 was also used with 486 processors. In fast, some motherboards with that chipset had sockets for either a 386DX or a 486. It was referred to as a hybrid chipset.

There exists a MR BIOS for this chipset: https://archive.org/details/3opr-001

Reply 9 of 22, by kingcake

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The Serpent Rider wrote on 2024-06-02, 17:15:

4 Mb was pretty standard when AMD finally released their 386 clones.

Yep. When the am386-sx chips came out this was pretty common. I have a Magitronic am386sx system that I got new in the box still factory sealed. It had 2 4MB 30-pin SIMMS installed.

Reply 10 of 22, by mkarcher

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dionb wrote on 2024-06-02, 20:46:
I call bs on that. […]
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mkarcher wrote on 2024-06-02, 19:15:

So while "there are no 30-pin EDO SIMMs" likely was true in 1996, there seem to be that many newly made 30-pin EDO SIMMs in circulation right now that this statement needs to be wiped from collective memory because it is outdated in 2024.

I call bs on that.

Just looked up "30 pin EDO SIMM" on eBay and got a pile of hits.

But... The first five that had legible chip codes showed:

(correct research results showing a lot of FPM modules sold as EDO stripped)

So despite SIMMs being labeled "EDO", the chips are clearly FP.

Sounds to me like some idiots (mainly, but not exclusively, at Keystron) thinking "DIMM=SDRAM, SIMM=EDO" and selling modules on that basis.

You are clearly correct that there is a lot of BS on ebay. I'm not sure about Keystron, though. Keystron also has a lot of offers marked as FPM, so it seems they somehow know that FPM and EDO are different kind of modules. Too bad that their big Keystron stickers typically cover the relevant part of the chip model number.

But I found one extremely fishy ebay offer, an offer titled "4MB 30pin EDO SIMM RAM MEMORY with parity 4x9 30-pin", with a Keystron sticker explicitly mentioning "EDO" on the parity chip, exposing the two data chips to extra scrutinity. They are HYB511740xBJL-60, with "x" marking a spot that has been primitively masked by overpainting it with a solid gray color that is only remotely similar to the chip package color. These chips could be FPM HYB5117400BJ chips (I didn't find a datasheet for "L"-type "low power" chips, though) or EDO HYB5117405BJ chips (again, the datasheets I found do not indicate that an "L" edition exists). Having the spot of the model number that differentiates between EDO and FPM "damaged" on the image on both x4 data chips is unlikely to happen by chance...

Reply 11 of 22, by eesz34

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dionb wrote on 2024-06-02, 20:46:
I call bs on that. […]
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I call bs on that.

Just looked up "30 pin EDO SIMM" on eBay and got a pile of hits.

But...

The first five that had legible chip codes showed:
"16MB 30pin SIMM RAM MEMORY 60ns EDO with non-Parirty 16x8 30p" HYB514100 4M x 1-Bit Dynamic RAM with Fast Page Mode
"16MB 30pin RAM MEMORY SIMM 60ns EDO with Parirty 16x9 30p" HYB511740 4M x 4 Bit 2k 5 V 50 ns FPM DRAM
"4MB 30pin EDO SIMM RAM MEMORY with parity 4x9 30-pin" HY5116100 16Mx1, FPM
"Siemens 1MB Sim 30-PIN 70ns GT-3009 EDO Memory" KM44C1610 16M x 4bit CMOS Dynamic RAM with Fast Page Mode. Also note that Goldstar GT-3009 is listed in a lot of other places and no one else claims that it's EDO.
"Texas Instruments TMS417400ADJ-60 1 6MB Simm 30-pin 60 ns 3-Chips Edo Ram" - yeah, the TMS417400ADJ is 4Mx4 DRAM, not a mention of EDO in the datasheet.

So despite SIMMs being labeled "EDO", the chips are clearly FP.

Sounds to me like some idiots (mainly, but not exclusively, at Keystron) thinking "DIMM=SDRAM, SIMM=EDO" and selling modules on that basis.

For what it's worth, I bought a pair of the 4MB 30 pin EDO SIMMs, item 153940236575, and it wouldn't work in a 386 I wanted it for. I returned it, and bought the FPM version from the same seller and it works fine. So this EDO thing on 30 pin SIMMs has me confused.

Reply 13 of 22, by eesz34

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jakethompson1 wrote on 2024-06-02, 17:09:

4 MB SIMMs would have been extremely expensive when 386 systems were current, and 16 MB is a lot of memory for a 386.

Oh I know. I didn't get past 4MB until I got a 486. My computer teacher in high school got a very early Pentium with 16MB and I just couldn't believe it.

Reply 14 of 22, by MikeSG

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The ALI M1217 / M6117d chipset is a 386 based system that supports EDO & FP DRAM. https://theretroweb.com/chipset/documentation … 14522658385.pdf

Supports 16MB SIMMs as well surprisingly.

"The DRAM controller supports Fast Page Mode DRAM
and EDO DRAM.The DRAM controller is capable of
accessing up to 64 MBytes of local memory, and
supporting four banks page interleave of DRAM using
256K, 512K, 1M, 2M, 4M, 16M single sided SIMMs"

Reply 16 of 22, by konc

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eesz34 wrote on 2024-06-02, 14:32:

Would it most likely expect FPM?

It's almost certain that only FPM will work on it. I've yet to see a 386 board that can work with EDO, or 30-pin EDO memory.

kixs wrote on 2024-06-03, 08:23:

Did 512KB and 2MB SIMMs ever exist?

Yes, bot of them! For a short time they weren't that uncommon either.

Reply 18 of 22, by mkarcher

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kixs wrote on 2024-06-03, 08:23:

Did 512KB and 2MB SIMMs ever exist?

Newer firmware versions of the Tekram DC-6x0 controllers contain explicit support for banks made of those SIMMs (or possibly soldered on-board RAM using the same configuration). While classic RAM chips usually have a power-of-4 size in bits (unless they are partly defective chips or double-decker chips), and most classic RAM chips are organized as x1 or x4 chips, you started to get SIMMs at these sizes when x8 chips with a power-of-4 size in bits started to appear. For example, the Siemens HYB514800BJ is a 4Mbit (still power-of-4) 512K x 8 DRAM. This chip basically is a "non-parity-SIMM in a single chip". I've rarely (if at all) seen 512KB or 2MB SIMMs referenced in memory support tables in mainboard manuals, though.

Reply 19 of 22, by rmay635703

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kixs wrote on 2024-06-03, 09:07:

Interesting. I've never seen them.

2mb 72pin simms were beyond common and quite frustrating because many 486 boards didn’t support double sided simms, many were intended for IBM or Compaq systems, one Compaq 386sx I own has a low density parity 8mb simm inside, good lord does that thing look like a cludge of a million chips

1mb 72 pin simms were extremely rare

512k and 2mb 32 pin simms were also rare and typically found in laser printers

One of my old PCCHIPS motherboards listed pretty much every simm size imaginable as being compatible in the manual

Including even strange things like 128kb simms

128k, 256k, 512k, 1mb, 2mb, 4mb, 8mb, 16mb were all in the list