How are different sized SIMMs and DIMMs — 16 Mbytes, 32 Mbytes, etc. — designed with different types of DRAM devices, such as 4M x 4, 2M x 8, and 1M x 16 parts?
Consider three different DIMM modules designed using 4M x 4, 2M x 8, and 1M x 16 devices: DIMM #1, DIMM #2, and DIMM #3. Remembering that DIMMs and SIMMs have a 64 bit and 32 bit wide data bus, respectively, the following examples can be applied to SIMM modules by using half the number of devices to span 32 bits. DIMM #1 ======= This is a 32 Mbyte DIMM using 4M x 4 devices in a single bank design. SIMM and DIMM memory modules accommodate one or two memory banks. This DIMM has the following characteristics: * a single bank implementation; * the memory is laid out to span 64 bits, so 4M x 4 devices require 16 parts per bank; * the addressing is common across all DRAM on the module and is multiplexed via RAS and CAS singles, as noted by Control; * the module has a density of 4M x 64 (address space of 4M by 64 bits wide), or 32 Mbytes. Note: Macintosh computers will size and determine the addressing mode (e.g., 4M x 4, 2M x 8, etc.) of memory modules at system startup. DIMM #2 ======= This
