Replacement RAM Chips

Generally the difference in chips is speed, density, pin layout (and number of pins and package type), voltage, etc. You should be able to cross reference the different types online to see if anything important is changed.

What the numbers mean varies a bit between manufacturers. In a few cases the numbers are arbitrary. I've always used 257 as synonamous with 256

Here's a good reference http://www.chipmunk.nl/DRAM/ChipManufacturers.htm

Wayne

You should be able to cross reference the different types online to see if anything important is changed.

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You would think. Anybody know of a good source or the proper way to look this up please step forward! :beige: Thanks.

http://www.chipmunk.nl/DRAM/ChipManufacturers.htm I use that link mostly for figuring out what ram simms are.

Can 128K RAM chips be identified by anything other than 4264, are there just as many variations?

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Way back, I had posted asking about RAM chips on a 128K board and was told they are a 4164 DRAM chip.

What's the difference between 4256, 41256-15 and 81257-15 RAM chips?
Do additional letters and numbers make a significant difference (e.g. 41256C-15)?

256 seems to be the main commonality between the chips, but 257 throws me.

All are used in 512K boards.

Can 128K RAM chips be identified by anything other than 4264, are there just as many variations?

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Welcome to the wacky world o' DRAMs. At the time of the 64kb generation (the time of the 4164/4264), there were relatively few variants. That quickly changed, however. NMOS gave way to CMOS ( the "C" in 41256C), page-mode was supplemented by EDO, access times headed south, and variations on allowed addressing modes proliferated like kudzu.

For the 128K, 512K and Plus, all you want is good old, plain-Jane page-mode DRAM. NMOS or CMOS would be fine, provided that the access times are compatible. EDO chips will not work in any of those. That limitation likely applies to the SE, SE/30 and Classic I/II, but I have not tried EDO memory in those models.

Stick with pure page-mode chips, and you will be fine.

NMOS gave way to CMOS ( the "C" in 41256C)

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So, in particular 41256 & 81257 DRAM chips are just different flavors of the same thing?

I use that link mostly for figuring out what ram simms are.

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Thanks. Unfortunately it doesn't help much with these old chips. For starters, none of those numbers come close to matching what's silk screened on the chips I have from the 128K/512K. They do match some of the numbers on the SIMMs from my Plus & SE though.

AFAIK, the X257 DRAMs are electrically- and pin-compatible with the X256 parts. An 81257 is (most likely) Hitachi's version of the 41257, with the latter being a CMOS version of the NMOS 41256. I can't say for certain, however, but that's my best guess.

According to the Apple Memory Guide January 2001, all desktop Macs numerically before the 4400 (Tanzania) used only FPM RAM, in 30-pin (or 72-pin) SIMMs, as tomlee59 observed. The use of EDO RAM (1k or 2k refresh rate) coincided with use of the 603e processor. All Compact AIOs therefore use 30-pin FPM SIMMs, at blazing speeds from 150ns to 100ns. The capacities of the usable SIMMs usually rise fourfold in a given Mac (ie, 256kB, 1MB, 4MB, 16MB), although both extremities of the range are not usually found in any but the IIcx, IIci (which can even use 512kB DIMMs) and IIvx, and a very few Macs (eg, Classic II) can use 2MB SIMMs. Apple seems never to have planned for use of 8MB in 30-pin SIMMs.

Chipmunk remains a useful listing, but, especially in the oldest RAM, has many frustrating holes in its listings.

de

Some 256Kx1 DRAMs that can be looked up at http://www.datasheets.org.uk/ appear at the end of this post. The trailing -NN access time speed designator should not be included in the part number lookup as its meaning will appear as an explanatory note within the base part number datasheet. The CMOS or NMOS designation is just a technology comment and should likewise not be put into the part number search field.

There are parts faster than the examples shown below. To look up a part datasheet requires knowledge of the part number, which may only be partially indicated on the part marking. The part marking often includes the mfg logo and some trailing digits, omitting the all important prefix letters and numbers. Faced with such a chip, you have to guess the mfg then from the examples that you know, add prefixes to try a search.

Given

4256 try SMJ4256

41256-15 try uPD41256, MSM41256, or KM41256 (one at a time!)

81257-15 try MB81257

41256C try uPD41256, then see if a C datasheet appears as a separate choice.

I leave it to interested readers to verify that page mode compatibility, or whatever, is met or not met by inspecting the datasheet of the parts at hand. The parts listed below are just examples of DRAM part numbers in use by leading manufacturers at that time. It's not a complete list, and most certainly does not imply fitness for any particular use.

100 NS

Hyundai HY53C256L-10 CMOS

Samsung KM41C256-10 CMOS, KM41C257-10 CMOS, KM41C258-10 CMOS

OKI MSM41256A-10 NMOS, MSM41257A-10 NMOS

Fujitsu MB81256-10 CMOS

120 NS

Hitachi HM51258-12 CMOS

Fujitsu MB81256-12 CMOS

NEC uPD41256-12 NMOS, uPD41257-12 NMOS

OKI MSM41256A-12 NMOS, MSM41257A-12 NMOS

Samsung KM41256A-12 NMOS

150 NS

Hitachi HM51258-15 CMOS, HM50256-15 NMOS

NEC uPD41257-15 NMOS

OKI MSM41256A-15 NMOS, MSM41257A-15 NMOS

TI SMJ4256-15 NMOS

Samsung KM41256A-15 NMOS

200 NS

Hitachi HM50256-20 NMOS

TI SMJ4256-20 NMOS