iMac G3 upgrade and RAM questions

[EvieSigma]

I acquired a pair of iMac G3s yesterday, a Bondi Blue Rev B and a 400MHz Indigo DV. I've never worked on these machines before so I've got some questions.

1. On the Bondi, I noticed what looked like a RAM stick inside a cage on the logic board. Is that VRAM or something else, and can it be upgraded?

2. Are there processor upgrades available for these iMacs?

3. The Indigo DV has what looks to be two different height RAM sticks and a weird amount of RAM (576 MB), is that normal? And can I upgrade the RAM past that?

4. What is the connector on the motherboard in the DV ahead of the RAM slots for? It has a white plastic holder for...something.

5. Does anyone have any mezzanine cards they'd be willing to part with?

I really appreciate the help, because I've got an interest in treating these machines right.

 

[rsolberg]

1. The slot inside the cage is system RAM. The slot is actually mounted to a CPU board and there is a second slot on the underside accessible by removing the cage, heatsink, and unplugging the CPU card. The Rev. B and later tray load iMacs already have 6MB of VRAM built in, where the rev. A machines have 2MB and a slot for another 4MB.

2. Tray load iMacs can be upgraded by removing the CPU board and replacing it with one from a faster tray load iMac. There were also a few third party upgrade cards available, but they seem to be very scarce. Slot load iMacs have the CPU soldered to the logic board.

3. The two different RAM module heights isn't specified. Someone has just installed two different height modules. 576MB means one module is 64MB and the other is 512MB. You could replace the 64MB module with another compatible 512MB one for a total of 1024MB/1GB of RAM.

4. The connector and holder by the RAM slots is for an Airport 802.11b wireless card. An adapter is required to connect such a card to the connector. That adapter was included with some, but not all Airport cards at the time. Airport Extreme cards are not compatible.

 

[EvieSigma]

Thanks rsolberg, you're the best!

The Bondi shows 256MB of RAM under About This Macintosh, so would that be solely the exposed RAM stick on the motherboard or a combination of the motherboard slot and the caged system RAM slot?

And I will have to try to find a faster CPU card, I'd like to upgrade the Bondi to 266 or 300MHz so that it will run OS 9 even better than it already does. 

I will have to track down another 512MB stick for the DV, do these iMacs take PC100 SDRAM like the B&W G3 or different RAM?

http://www.ebay.com/itm/131970846036?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

This is a tray-loader CPU card, correct? 

 

[Gorgonops]

Thanks rsolberg, you're the best!

The Bondi shows 256MB of RAM under About This Macintosh, so would that be solely the exposed RAM stick on the motherboard or a combination of the motherboard slot and the caged system RAM slot?

I think there's some confusion here.

There's no "motherboard slot" for RAM. That stuff in the slot on the motherboard is VRAM. The Rev. A iMac shipped with that slot empty while the B-D revs came with it populated. All memory is on the CPU card inside the cage. You can only see one slot because the other slot is on the *bottom* of the CPU card, IE, you actually have to yank the CPU card out to get to it. If your system has 256MB of RAM I'm going to take a wild guess that both the top and bottom slots on the card are filled with 128MB SO-DIMMs. (I think when those systems were shipped they came with a 32MB SO-SIMM in the secret hidden slot and the top one empty, so the system has already been upgraded once.)

The computer can go to a maximum of 512MB but it's sort of difficult to find 256MB SO-DIMMs that are compatible with it. Most 256MB SO-DIMMs you'll find in circulation use denser RAM chips than the Mac's memory controller can deal with, so they'll either show up as 128MB or not work at all. If you're going to try to go all the way try to buy the chips from someone that will guarantee they're compatible.

 

[EvieSigma]

Oh, okay! Yeah, there was some confusion...I'll have to go hunting for compatible SODIMMs, but I think that might wait until I buy a CPU card since I'm planning on replacing the stock 233MHz CPU anyway with that 333MHz card I linked to.

Also, is there any kind of software utility for OS 9 that will actually tell you what processor your Mac has? For all I know, since someone upgraded the RAM, my Bondi might not have the original CPU card anyway.

 

[Compgeke]

If you have OS 9, System Profiler will report the CPU and speed. On 3rd party G4 upgrades and such it might report wrong but if you see 233 I'd bet on it being the stock CPU. Ram was cheap, CPU upgrades were almost more than the system was.

 

[EvieSigma]

Yeah, I ended up finding that out on Google, but it's still appreciated.

 

[EvieSigma]

I hate to necro a thread, especially my own thread, but I did a little research and apparently the tray-loaders take PC100 CL2 SDRAM, which I was able to find on eBay relatively easily?

http://www.ebay.com/itm/Smart-SM572328574D9BPICE-256MB-144p-PC100-CL2-18c-32x4-ECC-SDRAM-SODIMM-Memory-/151573458381?hash=item234a7b6dcd:g:i9YAAOSwBahUzUJU

The only thing is, apparently the SODIMM slots take different height SODIMMs and the only 512MB PC100 CL2 modules I found are ECC, which I know Macs tend to have issues with. I don't know how to determine the height of a SODIMM from an eBay listing...

And to add to the confusion, one site says PC66 and the other says PC100! Which is it?

 

[Gorgonops]

The only thing is, apparently the SODIMM slots take different height SODIMMs and the only 512MB PC100 CL2 modules I found are ECC, which I know Macs tend to have issues with. I don't know how to determine the height of a SODIMM from an eBay listing...

 
512MB modules simply *will not work* in the tray-loaders. Period. Long story short: The "Grackle" RAM controller in the iMac supports 8 "banks" of RAM, the maximum size of a bank is 128MB, and each physical DIMM slot in the unit supports a maximum of two banks. The RAM controller simply can't see more than that in a single slot. These banks size limitations are typical for SDRAM controllers of this era; the very popular 440LX/BX/MX chipsets for Pentium Pro/II/III/Celeron CPUs have similar limitations and in fact this discussion here might be slightly useful in helping understand why there are so many 256MB modules that *don't* work in the iMac; either they're a single too-large bank or their internal arrangement otherwise requires a refresh scheme the Grackle and other old SDRAM controllers don't support.
As for whether it's "really" PC66 or 100, well, technically you could argue it's either both or neither. The machine runs the bus at 66mhz but it requires aggressive RAS/CAS timings that some PC-66 RAM modules can't handle. (PowerPC Macs have a well-earned reputation for being "pickier" about RAM than most PCs; that's because PC BIOSes are usually willing to reprogram their refresh controllers based on what the little ID ROM on the module tells it or pick a slow least-common-denominator setting if said data is corrupted, which it sometimes is on cheap modules. Macs usually expect what they expect and either won't work at all or behave badly if they don't get it.) I think the "PC-100" recommendation is simply based on the guess/hope that any random "100mhz-rated" module is likely to live up to its expectations.

 

[Gorgonops]

... anyway, not sure why you'd want to pay $25 on eBay when OWC has SODIMMs they claim will work for only $17:

https://eshop.macsales.com/item/OWC/100SO256168L/

 

[EvieSigma]

I was just going off tech-specs from LEM and EveryMac, with LEM mentioning PC100 and EveryMac mentioning PC66. 

I'll have to try the OWC ones. Worst comes to worst, they'll probably work in a late 90s laptop or something.