Excellent questions. You're on the right track and you have the right basic idea.
Old systems could only use about 3.5 GB of RAM but new ones will use much more.
((This is because of the 32 bit OS vs the 64 bit OS. Any new OS will most likely be Windows 7 64bit or newer))
Typically when you look at a game it might say something like 4GB recommended. That means that the game will process enough information rapidly enough to fill up 4GB. However some games can and will use more if you have it.
Most new systems come standard with 8GB because typically games and high end software can easily suck up 6 or 7 GB's at a time. The extra couple GB of RAM are so if you try to run other programs simultaneously - Ex: Skype, Browser, Music Players, etc...
So ideally you want 8 GB, if you are ready to spend the money then getting 16 will give you lots of extra room for future expansion (you can go as high as 32 in really high end systems but it's overkill.)
Now onto the topic of types of RAM - Gaming Vs Standard.
Standard RAM looks like (This is an older model but typical RAM looks the same with black chips showing):
Gaming RAM usually looks more like this:
The plating on the outside of gaming RAM allows the even distribution of the heat that's generated as the component is put under stress(heavy loads) while gaming or doing other complex tasks.
This plating also allows heat dissipation as air flows in your computer case. The little fins on the top supposedly help with that as well but it's as much about style and looking good as it is cooling.
A cool RAM component will perform faster and be less likely to wear/crack as it heats up because it doesn't get as hot.
Now RAM chips are much the same as processor chips so the architecture/design that goes into making them can also impact how they perform. I can't tell you much here because traditionally those are manufacturer trade secrets.
So we move onto CAS Latency. Which is exactly what it sounds like. It's latency. This latency represents the time delay between when the message is received by the memory(RAM) and how long before it responds to the message it received. In other words how fast it processes that information.
Ideally you want a stick of RAM with a CAS Latency of 9 or less. You'll often see a series of numbers along with it like "Timing: 9-9-9-24-2N." RAM sort of works like a spreadsheet and those numbers basically represent how fast information is transferred from cell to cell within the spreadsheet. So the lower the number the faster the RAM is.
This is an example of good RAM for gaming with:http://www.newegg.ca/Product/Product.aspx?Item=N82E16820231536G.SKILL Ripjaws X Series 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model F3-12800CL7D-8GBXM
DDR3 1600 (PC3 12800) Timing 7-8-8-24
Cas Latency 7
So in that example...G.Skill
- is the name of the company. Ripjaws X Series
- is the name of the RAM (like the Mustang in Ford Mustang)8GB (2 x 4GB)
- tells you how much and that there is 2 sticks of it at 4 GB per stick. ((This is a good amount.))240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
- Tells you basically what type of RAM it is and this is the part that you compare to your Motherboard to make sure your motherboard choice will work with this RAM and vice versa.
- The rest of it is specific model numbers and stuff. It doesn't mean anything for the consumer.
Basically you can't go wrong with any RAM of DDR3 1333 or 1600. I prefer the cooling, the look, the price, and the reliability of G.Skill.
For more detailed explanation of RAM timings and CAS you can look this multiple page article over: http://www.hardwaresecrets.com/article/Understanding-RAM-Timings/26
Now there's one more topic to briefly skim over here... Dual Channel Vs Triple Channel.
Basically these sticks of RAM are designed to perform optimally when grouped together as 2 sticks (dual ch.) or 3 sticks (triple ch.).
It will say on motherboard it if it's "triple channel" usually(Nehalem type) but those are rarer and far more expensive.
I suggest going with a dual channel (2 stick) memory kits because they will work with most board types.
Triple channel is better then Dual but if you buy more RAM in Dual Channel it's always better then a little less in triple.
Just make sure that your mother board has enough slots/sockets to stick them into.
As for how it works, it's basically the difference between you're processor using a spread sheet with 2 columns or 3 columns. The more columns it has access to the more information it can pump into it. AT this stage though the cost for 3 ch. is to excessive for the little difference it makes.
The conclusion is more RAM is always better but 8GB DDR3 1333 (or 1600) is enough for any current gen game running at full Ultra settings.
When picking RAM, a lower CAS Latency and timing numbers are better choices.
So when you make your decision check out the motherboard and make sure that it has some room for expansion. Often you'll see it say something like "Maximum Memory supported 16 GB or 32 GB." You want at least 16 GB for future expansion.
RAM Memory is actually one of the least important things to think about when picking computer components.
If you focus on Processor and Motherboard then the RAM can always be upgraded later. It's the cheapest and easiest part on a computer to replace. Just make sure the motherboard supports some faster RAM and has space for more sticks of it in the future. Feel free to buy cheap now then later on you can go with fancy expensive RAM and swap it out.