Need help in clarifying about pre-SDRAM era laptop RAM types

[kfzhu1229]

So I have this old 1995 Dell Latitude XPi P75D laptop with a Pentium 75Mhz CPU, VGA DSTN colour display and 8MB of onboard RAM.
However, I want more RAM on the thing.
I have had a look inside the RAM door and that thing takes 2 72pin RAM sticks, so I bought a pair of 16MB sticks.
However, it does not work at all. The RAM was tested before being sent to me so that should be good.
So now I am getting confused with the RAM types for 72pin for laptops. Is there the FP type for laptop 72pin as well? If so where can I find such sticks?
The ones I bought are 3.3V EDO type and it would make sense if it's not working because of FP vs EDO
I do know that ThinkPads at that era do not use this kind of memory, but I think HP omnibooks and Toshiba satellites at that era should.

[rkawakami]

FP or FPM is Fast Page Mode memory. EDO is Extended Data Out. FP came before EDO. You should be able to use EDO memory in a system that was designed for FP but not the other way around. From what I can tell searching the internet, your Dell system was designed to use FP memory, ergo, either memory type should work from what I know. Do you know what speed option the new modules are? Usually it's a number after a dash at the end of the part number.

What does "However, it does not work at all" mean? Does the system not boot? Does it not pass POST?

Do you have a copy of memtest86+ that you can boot the system with in order to test the memory? https://www.memtest.org/

[kfzhu1229]

FP or FPM is Fast Page Mode memory. EDO is Extended Data Out. FP came before EDO. You should be able to use EDO memory in a system that was designed for FP but not the other way around. From what I can tell searching the internet, your Dell system was designed to use FP memory, ergo, either memory type should work from what I know. Do you know what speed option the new modules are? Usually it's a number after a dash at the end of the part number.

What does "However, it does not work at all" mean? Does the system not boot? Does it not pass POST?

Okay so I believe it uses FPM as well. And it should work with EDO because I used a multimeter and detected 3.3V power on the RAM stick, which is correct for EDO, despite the laptop is designed to use with 5V FPM sticks originally.
Unfortunately the RAM sticks do not have any labels on it. But the chip model number does suggest it's a 60ns model.
I have tried modifying the presence detect pins in all sorts of other ways and no luck.
Sometimes the machine would turn on but the RAM does not do anything, and at other times it halves my onboard RAM to 4MB!
When it does not turn on, I mean the power light comes on, hard drive spins, but nothing else. When it's working with the onboard RAM, the 3 keyboard LEDs should flash briefly and then the screen comes on, but it doesn't even get that far with these RAM sticks.
So my analysis is that probably it is because these are high density sticks over here or something. The seller puts a picture of a 8 chip config of the same EDO RAM, but I received a 2-chip config instead!
Maybe it's also like high density 256MB/512MB PC133 SODIMMs that those do not work on a PC100 or PC66 machine like a T22 or 600?
Having no luck with what kind of RAM actually works with the XPi on the internet (the discussions are all for XPi CD, which is a much newer Pentium MMX based machine), I saw someone else selling a XPi with 32MB of RAM on eBay. So I asked him if he can send me a picture of what his RAM looks like, and here it is:
https://i.ebayimg.com/images/g/LWkAAOSw ... -l1600.jpg
I believe one of them is a 8MB stick and the other is 16MB, together with the onboard 8MB gives 32MB.
Here is how mine looks like (note mine are all single sided 2 chip sticks):
https://1drv.ms/u/s!At7-rt1KJ7WviPw4pFX ... A?e=3b02Tk
So can someone verify that my theory about the density of the RAM can really be the problem why I cannot get it to work?

[RealBlackStuff]

According to the specs I found, those Samsung chips on your modules can do both FP and EDO and handle 3.3V and 5V.
https://www.alldatasheet.com/datasheet- ... 1204C.html
It sounds reasonable that your machine expects low-density (e.g. 4 or 8 chips) rather than high-density (2 chips) RAM.
But memory-engineer Ray will know that much better than most of us.

[rkawakami]

Your analysis seems to be correct but there's also a question of module size.

Your two-chip modules have Samsung KM416V1204AT-6 parts on it which are 1Meg x 16 60ns EDO devices. The total memory on that module is 4MB. I could not find a 1204AT datasheet but the 1204C version is 3.3V with 1K/16ms refresh (as opposed to 4K/64ms refresh).

ref: https://pdf1.alldatasheet.com/datasheet ... 204BJ.html

The eBay seller's 8 chip module in the lower slot has Samsung KM44V4100ALS-6 devices. Those are 4Meg x 4 60ns Fast Page devices with 2K/32ms refresh and have a total of 16MB of memory if there's actually 8 chips on the board.

ref: https://pdf1.alldatasheet.com/datasheet ... 4100C.html

The upper slot has Samsung KM48V2100ALT-7 parts on it. Those are 2Meg x 8 70ns Fast Page devices with 2K/32ms refresh and again, if there's 8 chips on the module it's a 16MB.

ref: https://pdf1.alldatasheet.com/datasheet ... 2100B.html

The "density" of the old DRAM modules, a la PC66/100 low vs high density, basically had to do with the way (amount and time) of refreshing the memory. The laptop's chipset generates a certain amount of refresh cycles within the specified time. The memory you install in the system needs to match those specs. I would suggest sourcing 16MB Fast Page modules that have 8 chips on them or 8MB modules that have 4 chips.