Banks versus Rows

Memory rows and banks are easily confused. Rows are physical groups and banks are logical groups. A bank comprises one or more rows, the number depending on CPU address bus width and the width of the memory, which is closely associated with its form factor.


These are 1 bit wide, and require eight chips per row (nine, if parity is used). The number of rows per bank depends on the CPU. XT-class PCs, which use an 8-bit memory bus, require one row per bank. 286s (16-bit bus) require two rows per bank. 386s and 486s (32-bit bus) require four rows per bank.

30-pin SIMM

These are 8 bits wide. 286s require two modules (rows) per bank. 386s and 486s require four modules per bank. Pentiums (64-bit bus) require eight modules per bank.

72-pin SIMMs

These are 32 bits wide. 486s require one module per bank. Pentium and higher systems require two modules per bank.

168-pin and 184-pin DIMMs

These are 64 bits wide. One DIMM always forms one bank.

168-pin and 184-pin RIMMs

Older motherboards use 168-pin RIMMs. Most newer motherboards use 184-pin RIMMs. Although most RIMMs technically use a 16- or 18-bit communications channel, a single RIMM appears to the chipset as one bank. Some motherboards have a single RDRAM channel, such as those based on the Intel 820 chipset, and allow RIMMs to be installed individually. Other motherboards, such as those based on the Intel 850 chipset, have dual RDRAM channels, and require that RIMMs be installed in pairs, one per channel. Note, however, that ...

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