memory source for 770Z

[Hamil33]

Does anyone know of a good source of 256mhz memory for the IBM 770Z? I have "Googled" 'til I'm blue in the face, only to end up completely confused about what will work and what won't work. I think I know that 66 and 100 speeds will work, but what about 133? I think I know that it must be low-density. Does low-density always have 8 chips on each side? I am currently at 320, using the built-in plus 2 128s. I know others have been successful going to 512. Any help will be welcomed.

[rkawakami]

Generally speaking, a good source of these slower (older) memory modules is either here in the Marketplace conference or on eBay. Looking up the specs of the 770Z, it originally takes 66Mhz SDRAM 144 pin SODIMM modules. As noted, this speed has been superseded by PC100 and then PC133. And yes, those PC133 modules may work as long as they are of the "low-density" design AND are the proper CAS latency (I'll get to that in a minute).

Just having 8 chips per side does not tell you anything about density. You also have to take into account the module's memory capacity. A 256MB low density module will have 8 chips on each side, but so does a 512MB module, but that one is NOT low density. A 128MB low density module will use a total of 8 chips (four per side), whereas a 128MB high density module will have a total of 4 chips (two per side).

CAS latency is a memory specification which says how many system clock cycles need to occur before you can begin reading data from the module. I am assuming for the moment that the 770Z is using memory timing which is rated as CL2 (2 cycle CAS latency). If true, this means that whatever module you install also needs to be CL2. I'm pretty sure that this is the case for all of the PC100 modules. However, most PC133 modules are NOT CL2 capable. Bottom line: if you stick with a module that is marked CL2, then you should be okay. If you are the experimental type, try plugging in a low density 256MB PC133 CL3 module and see what happens. I don't have a 770Z, otherwise I'd try it myself.

If you stick with a 256MB module that has an IBM FRU of 33L3069 or 33L3070 then that should work for you. However, most eBay auctions which list those part numbers seem to end up at higher prices than for a generic PC100 256MB listing.

edit: To clarify CAS latency... A module marked as CL2 will also work if the system is actually CL3. The reverse is not true; if the laptop uses CL2 and is fixed at that speed, then you cannot install a module marked CL3 and expect it to work. This is also assuming that none of the special memory onboard the module has been tampered with or changed (in technical terms, the SPD, Serial Presence Detect, information stored in a separate memory).

[al7kz]

The 256 chips from Crucial for the T20 do work in the 770z. They are PC133, CL2. I'm currently at 512mb in my Z:

Slot 0 (mainboard) - 128
Slot 1 - 128 (PC66, CL2)
Slot 2 - 256 (PC133, CL2) Crucial

I tried 2x256 in slots 1 & 2 but that disabled the mainboard memory to get only 512. I would be nice to get >512 somehow. Cheers...

[Hamil33]

Hey, al7kz

You indicate that you have a 128 chip on the mainboard. Does that mean that you changed out the original 64? Assuming that to be the case,did you find it difficult to get to that chip? According to diagrams that I have seen, it is a major job to get that deep into the "innards" of the 770Z to change that onboard chip.

I will pursue the 133mhz route, in all probability.

Thanks again for all the responses.

[al7kz]

Hi Hamil33,

That's right. When my 770Z died I replaced the 64 chip with a 128 during one of the three or four rebuilds. It is a pretty major job to get to that chip, since you have to take virtually everything out of the box to get to it. But the HMM instructions are pretty good, and if you take it slow and pay attention to screw types and sizes it shouldn't be bad. I also tore down the screen, which it turned out later I didn't have to do.

I think in your case I would just write off the 64 onboard chip and put in 2x256 in the outer slots. Tearing down the machine for 64mb may not be worth it. Cheers...

[Hamil33]

Thanks for the suggestion. I am assuming that means that if you use both available slots for 256s you will still only get 512 even though the onboard slot has the original 64. I can imagine the hassle of changing the oridinal chip.

[Wingnut]

The 256 chips from Crucial for the T20 do work in the 770z. They are PC133, CL2. I'm currently at 512mb in my Z:

Slot 0 (mainboard) - 128
Slot 1 - 128 (PC66, CL2)
Slot 2 - 256 (PC133, CL2) Crucial

I tried 2x256 in slots 1 & 2 but that disabled the mainboard memory to get only 512. I would be nice to get >512 somehow. Cheers...

I don't know if this is the case for the 770's too, but my 600 was quircky when it came to reading memory. It originally took PC66 memory. I tied putting 2 x 256 sticks in it that were PC100 and it only read 416 (a 256 stick, half of the other 256 stick and the 32 OB memory)

So I experimented a little. It turns out, if I put a PC100 stick in one slot, it read it all. If I put it in another slot, it only read half of it. Bottom line, if I wanted to maximize my RAM in the 600, I would have had to buy 1 x 256 stick at 66mhz (very hard to find and not cheap). So instead, I put a PC66 128 stick in one slot and a PC100 256 stick in the other and got the same total of 416, but didn't have to waste a 256 chip.

Maybe your 770 is similar and it was reading your onboard just fine and just reading the second 256 at half speed?