Majority of the Pentiums computers have 2 banks of two SIMM sockets on the motherboard, each bank must have a pair of same value and type of memory to be utilized by the system.

Most Pentiums computers uses 72 Pin SIMMs. Installation requires 2 SIMMs per bank to upgrade. (2 sockets per bank)

Typically, Pentiums Computer with frequency of 166MHz and up have SIMM and DIMM sockets on board and use 168 Pin DIMMs and 72 Pin SIMMs on the same motherboard.
Pentium computers utilizing 168 Pin DIMMs require 1 DIMM at a time, (1 socket per bank.)

Memory Types: Generally EDO (extended data out) DRAM in matching pairs. Older Pentium computers (60MHz -100MHz) require FPM (Fast Page Mode DRAM.) Newer 100MHz to 200MHz MMX computers, CYRIX 6X86 and AMD 586 class processors uses EDO or FPM, and in some machines SDRAM (DIMMs.)