PowerMac 6500 RAM question


Simply Daemonic
Hello to all,
Here is a big question for you serious mac techs.
I have a friend of mine that consults me for his mac stuff and I fix his mac when ever it's screwed up.

With RAM prices so low these days he wanted to up his RAM. I went to the apple tech spec site and for his model (6500) the max RAM is 128Mb.

Somehow he has the idea that I told him that his mac *could* take 256Mb total RAM. I dont recall this but anyway.

The question here is this:
Can his mac be forced to accept 256Mb or not ?

Is it a hardware problem (i.e. one just can stuff his mac with the chips he bought) or is it a soft/firmware problem (i.e. no matter how much RAM you put in there the mac is going to only see 128).

I don't know the specifics like how many chips he bought but I am pretty sure he go 168 DIMMs which is what a 6500 takes (according to apple's tech spec site anyway).

I am probably going to have to see this ailing mac sometime soon to fix it lol. so....
What are your opinions ???

A 6500 takes 168pin sticks? Are you sure about that? My old 7100 took the 72pin variety.

This series has two DIMM slot that use 168-pin DIMMs (these are NOT the same as the 64-bit wide 168-pin DIMMs used in the 73/75/76/85/86/95/9600 series systems). Currently the largest DIMM of the type that this series takes is 64MB (at a street price of between $55 to $65), giving the systems a max of 128MB. (Note: the motherboard configuration is the same as the Performa 6400)
In case anyone is still interested, 6400/6500 macs will NOT USE SDRAM. Don't even try. 6400/6500s use 5-volt 168-pin FPM DIMMs but they will also run 5-Volt buffered EDO DIMMs and those are more easily found today (2005) than the FPM DIMMs.

However from what I understand, the 6400 and maybe even the 6500 run EDO DIMMs in FPM mode. 73/75/76/85/86/95/9600 PowerMacs also run the same 5-Volt 168-pin buffered EDO DIMMs.

BEWARE: there are lots of 168-pin EDO DIMMs for sale on the internet, but most are 3.3-Volt and will burn out in a Powermac and possibly ruin the powermac itself. HP or Compaq EDO DIMMs will not work in a Mac.

Currently, 64MB DIMMs from www.datamem.com, a longtime Mac generic RAM distributor, are $19 each. 128MB DIMMs are $23 but they have a 4K refresh mode that may cause a 6400/6500 to recognize only half the DIMM.
I'm not sure but it may be that the 6500 will recognize the EDO DIMMs and
use them in EDO mode.

There's a great Supermac Insider web page that describes the DIMMs (remember the SuperMac clones?):


Can't find the web page? Google this: supermac insider memory identification
You are exactly right. This is the situation with my Motorola StarMax as well. It takes 168-pin EDO DIMMs. From just looking at them, they loook evry much like the PC-66/PC-100/PC-133 variety of RAM, but they are not. And PC-xx SDRAM will not work on these models.

Depending on the Mac, these DIMMS will either need to be 5v or 3.3v. DO NOT USE THE WRONG VOLTAGE AS IT AN DAMAGE YOUR MAC.
jonkx said:
...but they have a 4K refresh mode that may cause a 6400/6500 to recognize only half the DIMM.
In the technical specifications I have for the 6400/6500 series, Apple states the following:
Note: This computer requires 1K or 2K refresh rate EDO DIMMs.​
I haven't tried any other DIMMs in any of those systems, but the fact that Apple took the time to note this requirement seems rather important to me.


Off topic...Wow, what an old thread! :eek:

Well, it is never too late to correct a mistake. In my 2001 post, I overlooked the fact that the 6400 series differed from the 6500 series systems (in the area of memory) in an important aspect... the 6400 comes with 8 MB on the logic board where as the 6500 doesn't (so the official max of the 6400 is 136 MB where as the 6500's official max is 128 MB).