Four.
They are installed in groups or banks of two. Most older motherboards that use SIMMs have one to three banks that can be filled with two, four, or six SIMMs. 72-pin simms are installed into groups or banks of two
30 pin SIMMs are installed in groups of four.
30-pin SIMMs are installed in groups of four. SIMMs in each group or bank must be the same type and size.
72-pin SIMMs must be installed in groups of two modules to a bank of memory
30-pin SIMMs are installed in groups of four. SIMMs in each group or bank must be the same type and size.
72-Pin SIMMs come in groups of Two in one bank.
two
four
30-pin SIMMs
When installing SIMMs into a Pentium system board you must use SIMMs in pairs in order to fill a memory bank. The Pentium has a data path of 64 bits and as such requires 2 SIMMs each being a 32 bit module to function.
Most motherboards today come with between 2 and 8 sockets for the insertion of memory. These are usually either SIMMs (single inline memory modules) or DIMMs (dual inline memory modules). These can come in different sizes. The motherboard usually labels these sockets "SIMM0" through "SIMM7" or "DIMM1" through "DIMM3", etc. The sockets are almost always filled starting with the lowest numbered socket first. Most Pentium class or higher motherboards require SIMMs to be inserted in pairs, but DIMMs may be inserted individually.
Natalie Simms & Jeff Simms :)