These chips are the system RAM and called "Permanent Main Memory". The Macintosh Portable uses 1 wait state when accessing memory locations in RAM. Because Macintosh Portable uses SRAM, there is no need to refresh memory as is required for dynamic RAM (DRAM).
The Macintosh Portable memory contents are retained when the Macintosh Portable is in Sleep mode, as long as the battery still has a charge. During normal operation the SRAM is powered from a +5V source. Because the SRAM chips are not selected, they do not consume much power.
The SRAM used in Macintosh Portable has a significant current draw when the chip is selected. The Macintosh Portable memory map is arranged as a 512K by 16 bit array. This is done by using 32 28-pin 32K x 8 SRAM chips. The RAM array configuration is such that only two chips are selected at any given time, leaving the rest of the chips in standby.
The Macintosh Portable can read RAM faster than the Macintosh SE due to:
