Home > Mac, mods, Technology > Upgrading iMac G4 to 640 MB.

Upgrading iMac G4 to 640 MB.

The iMac G4 is unique, as far as I’m aware, in that it has two memory slots which take different types of memory. One slot is easily user accessible with nothing more than a screwdriver and takes a 133MHz laptop SO-DIMM, up to 512MB.

The other comes factory preinstalled (in this case with a 128 MB, 133MHz DIMM), but is much harder to access, requiring disassembly with a set of Torx (star) drivers.

Upgrading to 640MB, then, is a simple task requiring about 5 minutes.

You will need:

  • A large area with soft padding to support the iMac in a lying down position.
  • A small, cross-head (plus) driver.
  • A branded 512 MB, 133 MHz, SO-DIMM for a laptop, preferably with a compatibility replacement guarantee, should things go wrong.
let’s get started:
  • Turn the iMac on its side. Take special care not to scratch the screen or the computer’s plasic casing.
  • Locate the four screws on the base and unscrew until loose.
iMac, getting the base off
  • Carefully remove the beautifully crafted aluminium base plate, revealing the RAM slot.
  • Ground yourself on something metal, like a metal door sash, a large metal desk or the kitchen sink.
  • Carefully insert the 512MB RAM stick in the slot at about 30 degrees angle from the base. Push the long edge very firmly, sliding the chip into the slot. 
With iMac open, insert the RAM.
  • Make sure the gold contacts are well in contact with the slots pins. When you are sure it is seated firmly, press down on the flat side of the chip until it is level with the base of the computer and the little tabs on either side clip into place.
Inserting the RAM properly
  • Make sure the chip is held firmly and the clips are properly clasping the chip.
  • Replace the lid.
That’s it. Power on and check the Apple menu, and About This Mac to confirm the memory.
You should test the system over night with a memory checker. I recommend:
Rember by Kelly Computing
You should now have an iMac with 640MB of RAM.
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