This article describes the difference between 64 and 128 megabit (Mbit) SDRAM technology.

Symptom

Apple Specifications support 128 megabyte (MB) SDRAM DIMMs using both 64 and 128 megabit (Mbit) technology on certain computers. However, the difference isn't explained.

Affected Products

• Power Macintosh G3 (Blue and White)
• Power Mac G4 (PCI Graphics)

As of the writing of this document, high capacity memory modules were possible by stacking two 64-Mbit chips placed together in the same package. Higher capacity SDRAM DIMMs would eventually be out of specification due to the number of lower density chips.

However, using 128-Mbit devices allow higher density memory DIMMs that meet the specification for power consumption, size, and performance.

In the case of the Power Macintosh G3 (Blue and White) and Power Mac G4 (PCI Graphics) 128 MB DIMM, that memory size is the point where either 64- or 128-Mbit technology memory devices can be used.

Important : 256 MB DIMMs must use 128-Mbit technology in order to be functional in the Power Macintosh G3 (Blue and White) and Power Mac G4 (PCI Graphics).