iBook G3 Clamshell not recognizing new RAM modules

As SDRAM evolved, high density chips meant that fewer chips on the card could produce greater overall capacity. For SO-DIMMs, this was a breakthrough. The same was true for DIMMs, but unfortunately a lot of the older Macs don't support high-density memory chips. As an example, the iMacs from 1999-2001 could not recognize high density modules. A 256 MB DIMM needed to have 8 chips on each side of the card, for a total of 16 chips. A 256 MB card with 8 high-density chips on one side wasn't compatible. A compatible 512 MB DIMM had to have 16 chips on each side, with 32 chips populating the card. You need to find an older SO-DIMM that doesn't have high density chips, which might eliminate current/recent production. I'd suggest checking ebay for pulled, older memory. I bought a lot of memory for Macs from a number of ebay sellers 15-20 years ago and never had a problem with compatibility. You just need to find non-parity, non-ECC, and non-high density chips. PC100 with CL2 would be my preference.

PC100 itself isn’t the problem. Apple’s original iBook documentation says the memory bus runs at 66 MHz and that 100 MHz SDRAM parts can be used.

The catch is that these iBooks are picky about the SO-DIMM’s internal organization and SPD information. A generic 128 MB PC100 module can physically fit and still be reported as incompatible.

Since yours has 64 MB soldered on the logic board, Apple lists 320 MB as the maximum, so you can use a compatible 256 MB module. I’d look for one specifically sold and guaranteed for the iBook G3 Clamshell/PowerBook2,1, rather than buying another generic PC100 stick. It should be a 144-pin, 3.3V SDRAM SO-DIMM.

The fact that the iBook runs normally with the module removed also points more toward incompatible RAM than an NVRAM or firmware problem.

Apple’s original specifications are here: iBook - Technical Specifications - Apple Support

That makes sense. The 144-pin/3.3V/PC100 specifications still don’t tell the whole story. Two modules with those same basic specs can use different SDRAM chip organizations, and an older iBook may accept one and reject the other.

The PC133 module is worth trying, but PC133 by itself doesn’t guarantee compatibility with the iBook’s 66 MHz memory bus.

Also, the fact that System Profiler can see a module but labels it incompatible makes a completely dead RAM slot less likely. It’s detecting something in the slot; it just isn’t able to use that memory correctly.

If the free module doesn’t work either, post the exact part numbers printed on the Siemens, IBM, and PC133 modules. Those would be more useful than just the PC100/PC133 rating and may tell us how the modules are organized.

For buying one, I’d still look for a seller who specifically guarantees compatibility with the original PowerBook2,1 Clamshell iBook, rather than a generic 144-pin SDRAM SO-DIMM.

Are the contacts on the memory module clean on your original memory? What about the RAM slot contacts?

Was the battery disconnected prior to removing & installing RAM?

FYI, there is more to memory compatibility than the speed/frequency. There are other memory timings which are also critical. If you go with a faster speed/frequency of memory, then those other timings can be tricky to navigate as some of them will also be faster while others may be slower. Those other timings which become slower could cause an incompatibility. IIRC, even if the speed/frequency is the same, but the CAS latency is lower, then some of the others may be higher. Note the "Latency" section of the following Crucial article:

https://www.crucial.com/support/articles-faq-memory/common-memory-specifications What is latency? The time delay between when a command (action) is entered and executed. In general, the lower the latency, the better. There are three numbers in the latency description. An example of this is a DDR4 module with 16-17-17 latency has a CAS latency timing of 16, a tRCD timing of 17, and a tRP timing of 17. Although CAS latency ratings are the most common latency rating, it’s best measured in nanoseconds. This is called true latency.

And here is a Kingston article going into more detail:

https://www.kingston.com/en/blog/gaming/cas-latency-cl-ram-timing-explained

For those PPC memory modules, the CL (aka CAS) was usually "3", but I always used modules with a CL of "2" and never had a problem (they were Crucial memory modules though). IIRC, back in the day if a device was supposed to use PC66 memory, then I would usually use the next speed up which may have been PC100, however, I don't think going two steps higher was ever possible back then (such as to PC133) because the latencies on the faster RAM would be incompatible. The Kingston article explains this a bit with some examples.

So if Apple said PC66, then only PC66 and PC100 would be compatible.....do not try PC133 as it probably won't be compatible.

I've forgotten a lot from those PPC days. I never had any issues buying Crucial RAM for PPC Macs based purely on technical specifications as I just described. I only encountered problems once Apple released the Intel Macs in 2006 where I had to make sure the memory modules were marked "Mac Compatible" by Crucial. I did this because I wanted to buy one set of memory which would work in both Macs & Windows PCs (some PCs could take more advantage of these faster modules).

Before using Crucial memory we had lots of memory compatibility issues. While the memory may use chips from respected manufacturers, the supporting circuitry on the RAM stick may not be of the same quality as the chips. Plus those off brand modules may contain half bad RAM modules sold at a discount to those off brands selling memory at lower costs (half bad RAM isn't necessarily a problem because they theoretically should be only using the good portions of the chips).

Often the difference is that your Mac uses non-ECC RAM. RAM pulled from PCs are commonly ECC.

I just looked up RAM for that model from the place I was always able to get RAM for ancient Macs. They no longer carry RAM for your model. Many of the sources that were our "go-to" RAM vendors have dried up.

If you are in the U.S., you might check in with PowerBook Medic

https://www.powerbookmedic.com/

They specialize in used/pulled parts. I've bought PowerBook G3 "Wallstreet" parts from them in the past, but it seems their current inventory levels are lower than before.

For identification when searching for RAM, this is model information that get used by aftermarket parts vendors to describe your Mac:

Model Identifier: Powerbook2,1

Model number: M2453

Order number for the Tangerine versions: M7619LL/A (Tangerine 3.2 GB); M7718LL/A (Tangerine 6 GB)

NOTE: the "LL/A" part indicates a model intended for the US market. If for another country/region, the last three characters may be different.

The above is from the MacTracker database. I one see only Tangerine model listed there.

Yes — that module is non-ECC.

The Infineon HYS64V16220GDL is a 128 MB, 144-pin PC100/PC133 SDRAM SO-DIMM organized as 16M × 64, and the datasheet specifically describes it as a non-parity module.

So the HYS64V16220GDL-7.5 you’re getting for testing isn’t ECC RAM. That part should rule out ECC as the issue.