Do DIMM's have to be matched?
As a general rule, a single DIMM fills the 64 bit data bus of the Pentium system. Although there are some exceptions to the rule, such as in the high-end server systems, most desktops do not require the memory modules in each slot to be matching sizes. If no mention is made of such, the general rule will apply and you can mix the sizes in each slot or bank. The largest capacity DIMM should normally be installed in the lowest numbered slot unless otherwise stated by the system’s User’s Manual or by the system manufacturer. This is to avoid possible timing issues.