I'd like to comment on the RAM frequency (1333/1600/etc) part. Generally, the best stick is the one that has the ideal combination of:
- lowest timings
- highest frequency
- lowest voltage
- lowest price
- being compatible with your motherboard.
But the first 3 factors are not set in stone. For example, if for the same price, you can get:
- a stick of 1333mhz ram rated at 9-9-9-9 at 1.5V
- a stick of 1600mhz ram rated at 9-9-9-9 at 1.5V
Stick #2 is the better stick here. Because if you "slow it down" to 1333mhz, you may be able to run it at better timings such as 8-8-8-8, or at 9-9-9-9 with a lower voltage, 1.4V perhaps, or just run it at 1333mhz and call it a day. They're practically the same chips, just tested to perform at the stated minimum specs. In other words, don't give up a good sale because it's a 1600mhz stick!
Compatibility is not set in stone either! If a 1600/9-9-9-9 stick doesn't run at this speed on a motherboard, it may actually run fine at 1333/9-9-9-9. Just like the 1333 stick of the same brand would. Of course avoid any stick you know beforehand may not be compatible.
And that is why most RAM default to 1333mhz in the BIOS: for best compatibility. It's often up to the user to configure it optimally (higher frequency, lower timings, or lower voltage) as per the rated specs, if he so desires.
Example
You can use CPU-Z to figure out the rated specs at different frequencies. Below are the specs for my ram module, officially rated 1600mhz, CL-9-9-9-9-24, 1.6V. This JEDEC table is embedded of the RAM chip itself.
As you can see, the official specs match the column for 1600mhz (actually 800mhz, remember DDR stands for double data rate). If I were to run the ram at 1333mhz (666), I could safely set the BIOS to run the RAM at 1.5V instead - in fact I should since anymore is wasted heat. At around 1200mhz, I could safely lower the timings to 8-8-8-8-22.
Now you may ask what timings could this particular ram achieve at 1333mhz and 1.6V? Unfortunately, that falls in the realm of the unknown (or the overclocking). In this case, it would be much safer to buy a chip that guarantees 1333mhz, 8-8-8-8-24 at 1.5V or 1.6V.
This means your motherboard accepts up to 32GB of memory. The BIOS is designed to allow up to 32GB, but has not been formally tested for this amount of memory.
If you are running Windows, make sure you are running Windows 7 Professional or Ultimate 64-bit (Home Premium can only accept 16GB), and as C2940680 noted, you may want to disable or manually limit the size of the pagefile, as it will be very large by default. Recent Linux kernels should have no trouble accessing this amount of memory.
Best Answer
DIMM stands for Dual In-line Memory Module and is the RAM module(s) on a mother board.
A dot in the 2 DIMM column means the memory will work when you put in two sticks of RAM. If there are 4 slots on the motherboard, you would put it in slots and 1 and 3 (normally, consult the motherboard user guide to be sure).
A dot in the in 4 DIMM column means the memory works when using 4 sticks of RAM.
If there is no dot, as in the case of the 1 DIMM column, then it indicates that the motherboard manufacturer did not test the memory using only stick of RAM.
If you read at the bottom of the PDF you linked to, it tells you...