Nothing serious. Maybe an error thrown during POST.

Thanks... Had a thought, that this is actually the case.
I just had to be shure 100%.

From personal experience, if you use EDO instead of FPM on a motherboard with no EDO support, it will not POST. I've seen this behavior on four motherboards with various chipsets (SiS, VIA, etc).

So. Basically speaking. EDO and FPM have same voltage and pin assignment or something like that?
Or different pin assignment, yet power-pins have same numbers?

Wich all in all, does no damage if wrong type is used?

Nothing bad will happen. If motherboard doesn't support it, it just won't post. Only late era 486 have support and most Socket 7 boards.

The issue of no-detection could simply be that non-EDO aware mainboards don't understand the 60ns pattern for presence detect.

http://www.ele.uri.edu/iced/protosys/hardware … arpoint-8MB.pdf

An experiment would be to change the detection to 70ns by shorting pin 69 (PD3) on the SIMM or mobo to GND, thus simulating a 70ns module. I'm not sure if the EDO timing will interfere somewhere else though.

h-a-l-9000 wrote:

The issue of no-detection could simply be that non-EDO aware mainboards don't understand the 60ns pattern for presence detect.

http://www.ele.uri.edu/iced/protosys/hardware … arpoint-8MB.pdf

An experiment would be to change the detection to 70ns by shorting pin 69 (PD3) on the SIMM or mobo to GND, thus simulating a 70ns module. I'm not sure if the EDO timing will interfere somewhere else though.

Then how do you explain the common 60ns and rare 50ns FPM modules?

As you can see in the links EDO memory requires support from the chipset.
http://www.pcguide.com/ref/ram/techFPM-c.html
http://www.pcguide.com/ref/ram/techEDO-c.html
The second link goes into what will happen if wrong type is used.
It (what happens) is chipset dependent and varies.
.

The second link only talks about mixing EDO and non-EDO, obviously on a board which supports EDO.

First link:
> EDO memory requires support from the system chipset.
Is the support needed to only take advantage of the better EDO timing or to actually use the memory? When comparing the timing diagrams EDO seems only differnt in that it holds the data for a longer time on its output.

50ns: If you look at the 'PRESENCE DETECT TRUTH TABLE' in my link you'll notice that 50ns is only specified for 16MB and 32MB modules.
General issue here is: How much of this truth table was specified at the point the mainboard/BIOS/chipset in question was designed? When they started with the 72-pin SIMMs they may not have known that there will be 60/50ns or even 32MB modules. When the board was made and 60ns modules were nor specified neither available at that time it can not be expected to know what to do with them. The hack above gives the mainboard something it knows so it can proceed to the next step.

60ns FPM has been around since 30-pin RAM.
I've seen 50ns 30-pin for IBM but that may have been 'retro' to upgrade older servers. - And probably proprietary.
.
If you look at the PRESENCE DETECT table 1Mb 100ns has the same code as 16Mb 50ns, 2Mb 100ns has the same code as 32Mb 50ns, others.
This is because they only designated 4-pins for PRESENCE DETECT and by the time 50ns was available they had run out of codes.
100ns was the older technology so naturally it's found on smaller modules and that's what they got rid of in the table to reuse it codes.
That should not cause any real-world problems as a board with a chipset that supports 16/32Mb modules probably isn't going have 100ns modules put in.
.
Quoting my second link:
>> In simplified terms, EDO memory has had its timing circuits modified so one access to the memory can begin before the last one has finished. <<
That is the fundamental difference between FPM and EDO.
IOW, they "tweaked it" such that data moves more often on the same clock/timing cycle. (But it only helps memory access.)
.

(The sketches are taken from https://www.tu-chemnitz.de/informatik/RA/news … m/section2.html )

If EDO was controlled like FPM, the difference would be the outputs are active longer (red). Question is, would that interfere with something in FPM mode.

h-a-l-9000 wrote:

Question is, would that interfere with something in FPM mode.

The second link I posted earlier says: sometimes yes - sometimes no. Depends on the chipset.
.
I personally haven't done any broad scope studies by sticking the wrong kind of RAM in all my mobos so I'll take their word for it.
.

Holy crap... Got more than I asked for. Didn't I ? 🤣

brostenen wrote:

Just qurious. What will happen if wrong type would be inserted, even though it is the same ns. speed? […]
Show full quote

Just qurious. What will happen if wrong type would be inserted, even though it is the same ns. speed?

I am thinking of, if one is to accidential using EDO ram in a board/expansion-card, wich only supports FPM.
And of course the other way around, using FPM in a piece of hardware that only supports EDO.

What would be the outcome of wrong mem?

Probably the board wont boot when inserting the wrong ram type..

The same as others have experienced here: The board will simply not post and no harm is done.

What influence does that PRESENCE DETECT TRUTH TABLE have if you do not use automatic memory timings in the BIOS?

feipoa wrote:

What influence does that PRESENCE DETECT TRUTH TABLE have if you do not use automatic memory timings in the BIOS?

I think none but the tables still give a clue as to what works.