Need help Identifying RAMs.

[crazyben]

These came with the Mac I recently acquired. I am still getting my feet wet on identifying RAM. Can you help me identify these and their size. If you can guide me on how to read these that would be very helpful. All I know is that these are 72 pins.

 

[Phipli]

So, all you need to do is Google the part number, for example "MCM514256AJ70" followed by "datasheet". "AJ70" doesn't really matter because it is just the package (size and shape) and speed of the chips.

Then follow links until you find a datasheet.

Open the document and verify it is for the correct chip, sometimes sites have the wrong document.

There are then two things you need to work out - how many "words" the chip is, and how big a word is. Chips in this era commonly have 1, 4, 8 and 16bit words.

Multiply the number of words by the size of a word (gives total number of bits) and then divide by 8 (this gives you the total number of bytes)... Then divide by 1024 (now kBytes), then by 1024 again... That number is now the number of MB in one chip.

Multiply that by the number of chips.

MCM514256AJ70 is ... 4bit words, 256k size, so 4*(262144)=1,048,576 bits = 131,072 bytes / (1024*1024) = 0.125MB

... 8 chips, so 1MB SIMM (assuming only chips on one side).

 

[Phipli]

It's also worth making note if the chips are EDO or FPM. FPM tends to be more compatible with Macs, but check the service source, because there are some macs that don't like FPM or EDO. And one that takes 3.3V RAM.

 

[Phipli]

The one with MCM517400 chips is 2MB per chip, so 16MB if there are only chips on one side, 32MB if there are on both.

 

[crazyben]

Thank you for detailed information. I will google and see what I can find.