I have an old build from 2006 that serves as a spare computer. I upgraded to Windows 7 on it and it's somewhat sluggish. I would like to add some additional memory to hopefully make things a bit more smooth. Do I need to match the exact timings on the existing memory if I want to add an additional 2 Gb (2 x 1GB)? It's PC3200 DDR if that matters.
I wasn't certain whether memory timings only matter between two matched pairs or if I needed to have identical timings for all four DIMMs.
Well, by default it's already configured with default timings.
If, one or more DIMMs have lower timings than the other memory, the whole memory will run at higher timings.
But it's one's preferance to set it to lower timings again, to make whole memory run at lower timings, through BIOS.
General rule of thumb is, if there are multiple kinds of memory (higher speed, lower timings), the system will run at the slowest one to make system stable.
Mainly you just need to be sure that you match the voltage (though some chips will run at higher or lower voltages it is best to match all modules for stability) - then you should also match the speed (ie. PC3200) since mismatching this will waste money (ie. the slowest speed will have to be used - though some chips will be stable at higher speeds !) - then come the timings - you will want to make sure the new ones at least match or are lower than the existing (again you can only set 1 set of timings for all modules so getting ones that are much lower is wasting $$ since lower latency modules are more expensive and you will not be able to use them at those tighter timings unless the other set is able to run faster than their spec) - but a module can run at any timing that is higher than it is specd for so if your existing module is CAS9 then any module specd for 9 or lower (ie. CAS8 or CAS7) will work but spending extra money for better timings is a waste since you will be forced to run CAS9 (again unless your existing modules run better than their spec and are stable at the CAS8 or CAS7 but not likely or they would have been sold as such !)