Can a mac take two ram sticks of different speed?

The difference in speed, in this case, shouldn't make a difference. The 450 should be configured for PC100, and PC133 will just clock down to match it. However ...

This model probably won't like 512MB sticks, nor will it like "high density" 256MB sticks (those with chips on only one side of the stick). The system will either (a) boot but only see half of the stick, (b) boot but not see the stick at all, or (c) refuse to boot.

Have you tried each stick individually to see if it "likes" or "dislikes" a particular stick?

Try a few things and report back.

How come you think this model won't like 512mb sticks? The specs are as follows:

CPU
CPU: PowerPC 750
CPU Speed: 450 MHz
FPU: integrated
Bus Speed: 100 MHz
Data Path: 64 bit
ROM: 1 MB ROM + 3 MB toolbox ROM loaded into RAM
RAM Type: PC100
Minimum RAM Speed: 100 MHz
Onboard RAM: 0 MB
RAM slots: 2
Maximum RAM: 1 GB
Level 1 Cache: 32 kB data, 32 kB instruction
Level 2 Cache: 512 kB backside, 1:2

The iMac boots fine from either stick and both sticks. Just once a while it kernel panics. A couple times while accessing classic mode and another while using "MacHelpMate" program.

Thanks.

I hate to say it, but your mismatched RAM is quite likely the cause of your issues. Apple's memory controllers are *picky*. And unfortunately no desktop Mac has every used techniques like ECC to catch errors non-destructively, so the only way you're going to know you have a problem is when you kernel panic.

Have you tried running the machine with just one of the sticks to see if the panics go away? (Knowing they're "gone" of course might require extensive testing, depending on how long it generally is between them.) Alternatively if you can dig up an "Apple Hardware Test" CD for your iMac (Apple used to bundle them with everything, but they're generally very specific about what machines they work on so you'll need the original one or one from a machine of very similar vintage) you could run the memory diagnostic test a few times in a row. I've found "bad" RAM will often make it through one test, but three or so loops usually turns up the culprit.

--Peace

My iMac g3/400 (very close to yours) ran for a couple years with one pc100 512MB and one pc133 512MB - like the last 3 macs I've owned, it was the most rock solid stable machine I could hope for.

Dana