G4 MDD (FireWire 800) Doesn't Recognize All Its RAM

[EvieSigma]

My G4 MDD (the FireWire 800 model with dual 1.25GHz CPUs) doesn't recognize all of its RAM. It has 4 512MB sticks installed but About This Mac only shows 1.75GB. I even pulled and reinstalled all the RAM. Could it be some kind of software issue? I'm running OS X 10.4.11.

It doesn't seem like bad RAM to me, because why would half a RAM stick be working and the other half not? I notice DIMM 2 shows up under System Profiler as being only 256MB, but it's clearly marked 512MB.

 

[Anonymous Freak]

If you move the sticks around, does the "half capacity" stick stay in the same slot, or does it follow the same stick?

 

[bunnspecial]

Some MDDs are unhappy with high density 512mb RAM. Depending on the specifics, HD512s may ether not show up at all or read at half capacity.

When you're buying Mac RAM, it's almost always a good idea to buy low density RAM. Non-ECC LD RAM will have 16 chips total(8 per side) while HD generally has 8 chips. The LD rule is pretty much universally true when you're installing the largest size modules that a particular computer will recognize.

 

[EvieSigma]

All four RAM sticks are exactly the same (NewerRAM 512MB), they came installed in the machine when I got it.

Swapping each pair of RAM sticks moved the "half-size" stick to DIMM0. How do I count the DIMM slots anyway? Relative to the CPU assembly, is DIMM 0 the closest or the furthest away?

 

[maceffects]

I hate to say it but around this time, Apple was switching to lead-less solder and inferior capacitors. I had issues with ram recognition on G4 and G5 machines.