Adding a 512 MB module alonside a 1 GB module

Install it. Matched pairs only becomes an issue when you have at least one matched pair to start with.

Most computers have dual channel memory that allows the matched pair to handle twice as much bandwidth. But if you have none to start with - their is nothing to "un-do" by installing another.

However what are the speeds of the two modules? The system will automatically reduce speed of all memory to that of the slowest. If the 512 MB is equal to or faster than the 1 GB there is no issue. If it is slower - you need to quickly calculate the impact.

If they are both the same, adding the 512 MB will approximately increase memory capacity by fifty percent for those applications using it - which should be most today. You might also consider the cost and advantage of adding another 1 GB stick to match the one you have. Then you will have dual channel with 2GB = 2 x 2GB = 4 GB compared to 1.5 GB for 1 GB plus 0.5 GB. Note that dual channel has to do with speed rather than capacity - but I think you get the idea.

I just checked and the B110 does not have dual channel memory, but the manual says there is a slight reduction in performance if the memory is not installed in matched pairs. It also means the benefit of adding another 1 GB chip is not as great as I stated - and it is the more expensive DDR memory I see.
Still adding 500 MB should give a nice boost in performance.

Do you have the Pentium 4 or Celeron processor?

If P4, do you know if your hyperthreading is turned on? I used my Dimension 8400 for 3 years before finding my HT was turned off in the BIOS. To see if it is turned on, just open Windows Task Maanager and select the Performance tab. Under CPU Usage History, you will have two separate graphs if HT is on. If you have only one graph, HT is off.

Celeron, unfortunately.

Also, I just checked - I have two 512-MB modules, not one 1-GB module (it only supports 2 modules). Thanks anyway though.