4MB of 80ns DRAM is soldered on board, and one 72-pin RAM SIMM socket is available for expansion. The sockets can accommodate both single- and double-sided SIMMs. Each single-sided SIMM can hold 1MB, 4MB, or 16MB using 1-, 4-, or 16-Mbit DRAM technology, respectively. Each double-sided SIMM holds twice that amount of memory.
Because the DRAM SIMM in the Quadra 605 and the LC 475 sits at a severe angle in the SIMM socket, there may be an interference problem with some third-party double-sided SIMMs. With the Quadra 605 and LC 475, there is minimal clearance between some of the components on the main logic board and the SIMM. You may also encounter interference with third-party SIMMs that have ICs placed too close to the edge of the PCB.
Remember, although several vendors make composite SIMMs that may work with your particular computer and application, Apple does not support composite SIMMs in any Macintosh. And 100ns SIMMs do not work in these Macintosh models: SIMMs must be have an access time of 80ns or better.
Before purchasing any third-party SIMMs, verify with the manufacturer that the SIMMs conform to Apple's specifications for your specific Macintosh product.