Watch out for motherboards with linear voltage regulators for the CPU since they can fail and ruin CPUs, unlike switching regulators that tend to shut down upon failure. A linear regulator should be no problem for a Pentium 166, but they've been known to be overloaded by first generation AMD K6 CPUs. If you see no coils next to the MOSFETs, assume linear and measure voltage before installing the CPU.
Don't use SIMMs and DIMMs at the same time since all the memory sockets are wired together, and the 5V chips on the SIMMs will gradually cause the 3.3V chips on the DIMMs to fail. SiS made some chipsets that were the exception because they kept the SIMMs and DIMMs on separate buses, allowing both types of memory could be used at once. Another unique feature of SiS was that SIMMs didn't have to be used in pairs. Some motherboards with both types of memory sockets had to be configured with the right type of memory installed or they wouldn't boot. In other words, you needed to set up with SIMMs before you could change to DIMMs, or vice-versa.
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