DIMM First Aid - 1.2

• Regarding the difference between what Apple System Profiler reports, and what DIMM First Aid reports, the author emailed me: "DIMM First Aid reports the fastest speed the DIMM will work at. Apple System Profiler reports the fastest speed the computer can run the DIMM at." So, this may explain why the specs label on some RAM boards doesn't match the specs that DIMM First Aid reports, but it's close.

• DIMM First Aid may not work unless your Mac's firmware is at least version 2.4.

• DIMM First Aid is able to write to the RAM board's EEPROM (the tiny chip on the RAM board), because, according to the author's email to me, "the EEPROM is connected to the motherboard via an I2C interface, which allows reading and writing."

• TattleTech is also able to report a RAM board's specs, including some data that DIMM First Aid doesn't translate, but I don't know yet how well the two utilities agree with each other.

• When DIMM First Aid reports "DIMM checks out OK", all this means is that DIMM First Aid has determined that the things it checks for, primarily the RAM board's CL2/CL3 characteristics, are compatible with the Apple firmware updates--not much more. It doesn't mean the RAM board's other specs are OK for the Mac that the RAM is installed in--I've found that RAM which DIMM First Aid reports as being OK (having correct CL2/CL3 settings), often won't work reliably in the Mac that DIMM First Aid is testing it in, if that RAM board is spec'd at a different bus speed than the Mac's bus speed--for instance, if DIMM First Aid reports the RAM board is PC133, it may not run reliably in a Mac that has a 100 mhz bus speed (apparently running a PC133 RAM board at CL2 speed doesn't compensate enough for running it on a 100 mhz bus, or something), at least in Macs up to the G4 AGP--later G4 models that have a 100 mhz bus speed might fare better with PC133 RAM, but I personally wouldn't take the chance. Also, RAM that DIMM First Aid reports "Incompatible number of column address bits" can still have DIMM First Aid reporting "DIMM checks out OK", since the number of column address bits has nothing to do with the CL2/CL3 settings, but you don't want to use RAM whose number of column address bits doesn’t agree with the specs of the Mac it's installed in.

• Many slower Macs like the G4 AGP can run fine for several years with PC133 RAM, but as the parts inside the RAM board and the logic board age, and their specs drift, a PC133 board will often cause trouble in a 100 mhz bus Mac--crashing, etc.--requiring you to replace the PC133 RAM with PC100 RAM.

• There are other RAM board specs that must agree with the Mac model they're installed in, like the RAM board's internal architecture (8 x 32, etc.). Usually, if you put a RAM board into a Mac whose RAM architectural requirements are different from the RAM board, you'll usually get an immediate and obvious problem--the Mac won't start up, or only half the RAM will be available, etc. DIMM First Aid's readme states: "DIMM First Aid will identify these DIMMs as having an incompatible number of column address bits." However, DIMM First Aid will still report "DIMM checks out OK" if the RAM board's CL2/CL3 specs are OK with the Apple Firmware Update.

• Even when DIMM First Aid reports "DIMM checks out OK", it can report any number of miscellaneous problems with a RAM board, like incorrect checksum, "SPD data revision is old or incorrect" and " SPD data revision is not set" etc.; these miscellaneous problems won't affect the RAM board's performance. However, sometimes DIMM First Aid reports some RAM as OK even when it has a problem with its CL3/CL2 data, like "CL2 and CL32 not set in Intel specification for 100Mhz support". Apparently this type of CL2/CL3 problem is not a real problem, since DIMM First Aid won't follow this up by saying you shouldn't use the RAM, but the type of CL2/CL3 problem that requires replacing the RAM, as DIMM First Aid will report, is "CL3 not supported", and possibly errors like "Fastest cycle time is slower than 15ns, this Mac requires 15ns or faster!", even if it appears to work properly. I think RAM that doesn't support CL3 can run OK in Macs that have a 66 mhz bus speed, but I haven't determined this for sure.

• To be safe, especially if your Mac is acting up even with a clean system, etc., replace RAM that DIMM First Aid reports various odd problems with, even if DIMM First Aid says the RAM should be OK.

agree with the other reviewers. I have a G4/dual 450MHz/512MB. After a recent clean reinstall of OS 9.1 and 9.2.1 upgrade, my 256MB DIMM 'disappeared' and System Profiler told me it was "not compatible," even though it's a PC100-222 module like the 126MB DIMM in slot 1, and even though I was previously running 9.2.1 and the firmware upgrade with no problems. This little utility solved the problem.