Timings and CAS Latency
CAS latency is one of the timings that you see in descriptions of RAM, so it will be addressed in the same manner as will the other timing numbers: briefly. The lower the of CAS latency the better. In fact in general, latency is a bad thing to have, you always want to avoid it. If your RAM has a CAS latency of 2, then it will be ever so slightly faster than RAM with a CAS latency of 3, assuming both are running at the same clock speed. The difference is quite small in most real world applications, but if you want to get the most out of your computer's memory, make sure it has a low CAS latency. For a more detailed look about how RAM works and what these timing numbers mean, check out ZeGermans' RAM discussion article.

Voltage
The amount of voltage your RAM can take is largely dependent on what type of RAM it is. The word “type” in the previous sentence has a dual meaning. The type of RAM you have could be DDR, or quite a few of you probably have what is called DDR2, the second generation of DDR memory. The differences between these two, understandably from the opening sentence, is mainly voltage. DDR2 RAM can operate at 1.8 Volts as opposed to 2.6 Volts on DDR for the same frequencies. This has some pretty massive implications in terms of both power consumption and overclocking, which for now we are not going to worry about. The other “type” of RAM you could have depends on what it says on the little DRAM chips on your RAM stick. The little white letters on each black chip on a RAM DIMM indicate from what company the chip was produced and what kind of chip it is. These little letters could read something like on the picture on the left, where the chip manufacturer is Samsung, and the kind of chip is TCCD.

TCCD? BH-5? 5B-G? ...?
For most casual computer users and even for most gamers, these little descriptions might as well not even be there, they are not important in the least. But for a select few gamers and any serious overclocker, they are terms to live by, they might even be the single most important factor in determining the success of your overclock. How can that be? They are just letters and numbers! Well, each of them mean something different. When semiconductor manufacturers like Samsung, Micron, Infineon, Hynix, or Winbond produce a chip, they have different characteristics. They have different voltage tolerances, different physical constructions, different appearances, etc. Interestingly, over the years of DDR's reign, these little differences alone have been some of the most scrutinized by the overclockers of the world. This chip will clock to these speeds at this voltage, this chip will clock to those speeds at this other voltage – it's all quite well documented and understood amongst the overclocking enthusiasts.

So what does this mean to you? Well, knowing the differences between all these terms will put you on the best grounds to determine for yourself what any given stick of RAM will be capable of when being overclocked. Most of the RAM related questions I get are usually about overclocking – Will this RAM allow me to overclock my (insert processor here) to 5 billion GHz?

Right then, on with the descriptions. The gross majority of enthusiast RAM on the market today are utilizing one of these 5 chips (or a close variant thereof): Samsung TCCD, Micron 5B-G, Micron 5B-D, Winbond UTT CH-5, Winbond UTT BH-5.

Samsung TCCD
This chip from Samsung is usually a dream for overclockers. The defining characteristic of a TCCD memory chip is its ability to reach tremendous clock speeds at relatively low voltages. Many people have reached up top ~300 MHz on TCCD at only 3.0V, which is the max voltage you would want to use for TCCD anyway. The advantages of the low voltage is low heat output. With other RAM chips, at high speeds the voltage is also high, causing for a high heat output which calls for active cooling. There is no active cooling needed for TCCD chips. The only real disadvantage of TCCD is that it is unable to maintain tight timings at high clocks. If you are running at 250 MHz for instance, you will probably have to had loosen up the timings to something like 2.5-3-3-8 instead of 2-2-2-6 at stock 200 MHz. Variants of TCCD usually have TC in common, TCC5 for example.

Micron 5B-G
Crucial is the poster child for Micron. One of the things that continues to draw people to Crucial's BallistiX series is their continued use of Micron chips, which are traditionally of very high quality. 5B-G kind of shares some of the characteristics of TCCD, in that it can reach a decent clock speed without having to bump the voltage much at all. It runs stock at 2.8V, but will run with tight timings and everything at 2.6V, and can reach up to around 250MHz at around 2.65V. That is really good considering your heat output will hardly be greater than stock. Timings will also be pretty decent at this level, you don't have to loosen them very much at all. However, 5B-G seems to hit a wall at around this voltage, and increasing it all the way up to its max of 3.6V will hardly do anything above giving you an extra 30 MHz and heavy temperature increases throughout your system. The max overclock for these kind of chips is around 280 MHz, and even at 250 MHz they offer a very nice overclock with a very little voltage increase – good stuff.

Micron 5B-D
Micron's 5B-D chips are very similar to the 5B-G chips in the sense that the stock voltages and max voltages are the same. However, 5B-D differs from 5B-G because you can get a higher max clock out of them. Also, 5B-D is generally unable to run at tight timings at higher clocks, and usually requires around 3.0-3.1V to achieve its maximum clock speed which is right around 300 MHz.