Memory Bandwidth vs. Latency Timings All memory is not created equal, nowadays you need to know which 'flavor' is best for an Intel or AMD PC if you expect
best performance back from your investment. When Intel released i865PE/i875P dual channel core logic alongside Intel Pentium 4C processors, memory game changed forever. With a DDR memory controller now capable of running dual channel, Pentium 4 was no longer to be bandwidth limited as it had been with i845 series. Those single channel DDR chipsets, like i845PE for instance, could only provide half bandwidth required by Pentium 4 processor due to its single channel memory controller.
As new 800 MHz FSB Pentium 4 processors allowed users to hit never before seen highs in terms of bus speed, many memory manufacturers were trying to capitalize on situation by releasing every increasing degrees of "high speed" memory.
Unfortunately, to run memory frequency at same speed as FSB (or a 1:1 ratio) almost all high speed DIMMs (Dual Inline Memory Module) have to have very lax timings. Often, these times are as low as 3-4-4-8!
Think about it this way, a car built for drag racing can go dead straight super fast, but cannot maneuver as well as an F1 race car. Likewise, F1 racer is good in corners but will be left in dust on drag strip. In other words, today's high speed memory modules are built for one thing only, and that's top speed, where timings really aren't considered all that much.
Memory timings play a key role in terms of overall system performance. More so in 3D based applications which do not need a great deal of bandwidth, but rather quick access between various pieces of hardware within computer.
Confused about memory timings?
When one talks about memory timings they're basically talking about how long system has to wait for memory to be in a ready state before data is fetched or delivered.
You could think about memory timings as people working at a drive through restaurant; you place your order then wait for food to be ready. The lower timings are, faster computer (and quicker your order comes) is able to get data from memory, and faster rest of PC will ultimately be. This rule of thumb applies whether you're on an Intel or AMD based system. As for why there aren't lower timings then 2-2-2-5, JEDEC (the memory governing body) does not think it's possible for current dynamic memory technology to run at 0 or 1.
When we refer to timings it is common to quote a four digit number separated by dashes (ie. 2-2-2-5). The first number always represents CAS (Column Address Strobe) Latency as it's usually most important.
Next in line is RAS-to-CAS Delay (Row Address Strobe), RAS Precharge and Act-to-Precharge Delay (which is always final, and largest number).
CAS latency is delay between registration of a read command and availability of first piece of output data. CAS latency is measured in clock cycles.
With all things equal, a stick of DDR memory capable of running 2-2-2-5 will make computer operating experience seem faster than a DIMM which may only run at 3-4-4-8. This is because delay from when memory receives an instruction, retrieves data, and sends it back out is less.
Where it starts to get confusing is when you has choice of buying high speed memory with slow timings. Just about every PC3700+ rated memory module we've seen uses conservative timings after all. If your answer would be to buy fast memory with tight timings, I'm afraid you're going to be disappointed as there are no such modules available yet. So, why are we still interested in fast memory with slow timings then? Well, answer goes something like this....
Why release fast memory with slow timings?
In highly competitive markets, once a major manufacturer releases a new and innovative product, rest will surely follow close behind. If one manufacturer doesn't follow suit, their products are considered 'old tech'.
