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

Its easier & faster to just try it on some 486 board that only supports FPM's.

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

Then texas instruments are the FPM one and the NEC is EDO?? Because the first one end with a zero..

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.

Ok, i thought it was the other zero.

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.

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 😈 .