RAM for Power Macintosh computers is provided by dynamic random-access memory (DRAM) chips, of which the first 8 MB of RAM capacity is soldered to the main logic board. Users may expand RAM capacity by adding 72-pin Single Inline Memory Modules (SIMMs) of 80ns or better (for example 60ns) in pairs of 4 MB, 8╩MB, 16 MB, or 32 MB in size.
For example, you may install two 8 MB SIMMs in the first two adjoining slots, additionally two 4 MB SIMMs may be added in the next two adjoining slots, and so on (no descending or ascending SIMM pair size order is necessary). SIMM pairs, of the same size and speed, must be installed in adjacent slots, but different size and speed SIMM pairs may be added to the next adjacent slots.
If you install a pair of SIMMs of different density, the Power Macintosh will assume they are both the larger size. For example if you have installed an 8 MB and a 4MB SIMM, your computer will think you have a total of 24 MB installed including the 8 MB on the logic board. In reality you would have 20 MB.
The result if an application were to try and use the additional memory that wasn't there, a system error or bomb would likely occur.
Article Change History:
15 Feb 1995 - Explained result if different density SIMM pairs are
installed.
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