RAM, if you didn’t know, stands for Random Access Memory, and to use the human analogy, its like your spine - the basis of communication between the brain (CPU) and the rest of the body. It is the memory that a CPU can read and write to at a speed many times higher than that of the hard drive. Generally, the more memory you have, the better you computer will run. Your OS will specify a thing called a swap-file. When your system runs out of memory, your OS will use this swap-file as a type of memory on your hard drive. The only problem with this is that your hard drive is many times slower than your RAM, and thus performance will suffer. With more RAM, your system will use the swap-file less, and you will see a performance increase. You can see this increase in loading a game of Battlefield 1942, comparing 256mb to 512mb of RAM. The system will use all your RAM up and continue onto the swap file, but as you increase your RAM size, it will use the swap-file less, and thus load a lot quicker.

Also, more memory allows more applications and processes to be running before your system runs out of memory, and stalls or crashes.

Speed/Type: Nowadays, there are virtually 2 exclusive types of RAM, with a very small 3rd type. The first two are: SD and DDR. SD is older and technically obsolete, running at a much lower speed. The key point of the RAM speed and type is to provide as much memory-bandwidth as possible to the CPU. Bandwidth is like a road. The higher the bandwidth, the more lanes on the road, and thus the more traffic the road can hold before becoming “saturated”. PC133 SD RAM provides 1.08GB/s of memory bandwidth. This was okay when CPU architecture could only handle that much (i.e. up to the end of the Pentium 3 range of CPUs, who just had 133 effective FSBs). But, with Athlon XP and Pentium 4 CPUs, this was hardly enough. Thats where DDR RAM comes into play. DDR stands for Double Data Rate, and runs and the speed is effectively doubled. First modules of DDR were suited to dual-pumped 100 FSB (200 FSB effective) Durons, and was called PC1600 because it provided 1.6GB/s of bandwidth. Now, with minimum FSBs of 133 (266 effective), 266 MHz DDR is the minimum you can buy, and its called PC2100 because, you guessed it, it provides 2.1GB/s bandwidth. DDR has continued on this path, right through to the latest PC4000 modules, at an effective speed of 500 MHz :O The third and rarely used type of RAM is Rambus. It was the pinnacle of RAM right through to when dual-channel DDR became available. It runs at insane speed and provides huge bandwidth, and is run in pairs. Its ratings refer to the speed - PC800 meaning 800 MHz. The highest commonly available RD RAM is PC1066 at 1066 MHz. RD RAM’s downfall is price - it is hugely more expensive than DDR to buy. The focus of the Pentium 4 architecture was RD RAM’s huge bandwidth, and a main reason why P4’s have such big FSB’s compared to Athlons.

This applies to Athlons especially. Athlon’s dual-pumped EV6 memory bus controller can only use bandwidth up to the FSB speed. This means that on my XP1800+, which runs at stock effective 266 FSB, the controller can only use 2.1GB/s (remember PC2100?) of bandwidth, and any more provided by the RAM is not used. The memory bandwidth “lanes” are blocked off. This is the main reason why people wish to up their FSBs on their Athlon XP’s - to take advantage of greater speed RAM’s bandwidth. Example: if i clocked my XP1800+ at 200 FSB (which i currently do, 400 effective FSB), my Athlon can now take up to 3.2GB/s bandwidth, and with the use of PC3200 RAM, i can “open up” the lanes on my memory-bandwidth road. This scenario does not so much apply to Pentium 4’s quad-pumped FSB, but with every increase in DDR speed, the DDR RAM can supply more bandwidth to the CPU. In P4’s case, the role is reversed. The CPU allows a much bigger road space than DDR can supply - there is grass on either side of the road. But with every increase in DDR speed, the road gets a little wider.

The following chipsets

Intel: E7205 Granite Bay, 865G, 865PE, and 875P
AMD : nVidia nForce2

support a new DDR feature called dual-channel. Dual-channel is where two sticks use two memory controllers together, to create a low-latency 128-bit memory interface out of two 64-bit controllers. Example: one controller can be gathering info, the other publishing it. They are independent of each other, but work towards the same end, and halve latency because of this. The memory bandwidth is also effectively doubled (think of the difference between a 64-bit and a 128-bit interface on a graphics card), provided the FSB can keep up with it. Dual-channel works best on Pentium 4 systems, as the FSB can allow this doubling of bandwidth, whereas Athlons only benefit between 5 and 10 percent. The other downfall of dual-channel is that for it to work best, you need matched pairs. Thus, same speed, same brand and almost same batch are required to get the most out of dual-DDR. Dual-channel can best be described by the road analogy : the road now has the same number of lanes coming the other way, effectively doubling the traffic through-put.

RAM timings are important, as they increase performance and decrease latency (lag). There are effectively 4 timings, which I’m not going to explain as they are a bit complicated and confusing

Column Address Strobe. Typically CAS3, CAS2.5, or CAS2. The lower the number the better.

The delay (in clock cycles) between when RAM is selected and when commands can be issued. Typical values are 1T (1 clock cycle) and 2T (2 clock cycles). The lower the better.

minimum Active to Precharge Delay. Once RAM is activated, it cannot be de-activated until tRAS has elapsed. Typical values at 5, 6 or 7, refering to clock cycles. The lower the better.

RAS (Row Address Strobe) to CAS delay. The delay between activating a row and reading the data on that row. Typically 2, 3 or 4, referring to clock cycles. The lower the better.

RAS precharge delay. Typically 2, 3 or 4. The lower the better.

Overall, aggressive (lower) timings are better, obviously, but you must find a balance between timings and speed. The difference between CAS2 and CAS2.5 in real performance is often very small, a couple of percent at most. Nice timings are the icing on the cake as far as I’m concerned. As for changing them - they’re usually in your BIOS somewhere, just dont do something stupid with them, okay? Otherwise you’ll either have a very unstable system, or your system won’t boot at all, and you’ll have to clear your CMOS.

Major RAM manufacturers:

• Corsair
• Mushkin
• GeIL
• Kingston
• Samsung
• TwinMos
• Winbond (also makes RAM chips)
• OCZ
• Crucial
• Kingmax
• A-DATA (makes RAM chips)
• Nanya
• Elixir
• PQI
• Transcend
• Hynix
• Micron.....

Top brands (this is subjective, and from my experience): Corsair > Mushkin > Crucial > GeIL > Winbond > OCZ > Kingston

Corsair, undoubtably the producer of the best RAM in the world, has outstanding RAM that will be guaranteed to run at extreme timings. Mushkin, relative new player to New Zealand’s market, is quite a bit cheaper than Corsair, and offers a range of top-quality RAM. GeIL has had some problems of late with quality control, but their latest “Golden Dragon” series of RAM seems to be top quality, and able to run in dual-channel modes at extreme speeds and timings. Winbond, a manufacturer and supplier of RAM chips to Corsair, Mushkin and GeIL also produce a budget type of RAM, thats not quite as fast as the other manufacturers, but is damn cheap to boot (we’re talking hundreds of dollars cheaper). OCZ have had a hard time lately, with a few bad modules tarnishing their reputation, but after restructuring are looking at the high-end market again with a range of dual-channel enhanced PC3200 and PC3500 RAM. Kingston have their famous HyperX RAM to their name, specializing in high-speed RAM to run in dual-channel, but they sometimes miss the mark.