|Your motherboard supports dual channel memory. So ideally for best performance you should have identical capacity pairs of memory in both slots.|
I had a quick look at the Dell online specifications for your model and it says the maximum memory is 4 GB though your post suggests 16 GB.
Your system supports:
Dual-Channel DDR2 SDRAM (533MHz)
Your system manual with regards to memory states:
Your computer has a minimum memory configuration of one DDR2 memory module. This memory module must be installed in DIMM1. If two or more DDR2 memory modules are installed, they should be installed in pairs of matched memory size, speed, and technology. If the DDR2 memory modules are not installed in matched pairs, the computer will continue to operate, but with a slight reduction in performance. See the label on the module to determine the module’s capacity.
Now to your question:
You currently have two sticks of 512 MB in each slot giving you 1 GB total dual channel RAM.
Your upgrade options are as follows:
2 x 1 GB RAM giving you 2 GB RAM in dual channel mode
2 x 2 GB RAM giving you 4 GB RAM in dual channel mode - This is your Max
What you are proposing is to put in 1 x 1GB memory in one slot. That will work. However, it will work in single channel mode and hence slower.
Furthermore when you want to upgrade later say to add another 1 x 1GB you may not be able to get a match to your original to create a matching pair. Some systems are not too fussy so long as both slots contain the same size and rated memory, others are more fussy. I do not know how yours will behave.
My view is go for a matched pair of 1 x 1GB. That way you get dual channel performance and it will be the better for it anyway.
Finally check your motherboard, does it have 2 slots or 4 slots? The manual suggests that it should have 4 slots.
If it does have 4 slots then your options increase.
For example you could add another 2 x 512 MB RAM in dual channel mode in the remaining two empty slots. This would give you a total of 2 GB (4 x 512 MB)
Personally in that event I would go for 2 x 1GB RAM in dual channel mode in the 2 empty slots. This would give you a total of 3 GB (2 x 1GB and 2 x 512 MB)
Hope it helps
☺ When everything else fails, read the instructions.