The Motherboard, Processor, and Memory - Types of Memory
(Page 11 of 18 )
Many types of memory have been used in computers throughout their development. Today, two types are common: high-speed, narrow bandwidth memory manufactured by Rambus called RDRAM (Rambus Dynamic Random Access Memory), and high-bandwidth memory called DDR SDRAM (Double Data Rate Synchronous DRAM).
Figure 2-13
A 184-pin DDR memory module
Rambus DRAM runs at higher frequencies than DDR memory. RDRAM is available at 800MHz, 1066MHz, and 1200MHz. Only certain Intel chipsets work with RDRAM, and it’s more expensive than DDR memory. The various speeds are referred to as PC800, PC1066, and PC1200. Like DDR memory, RDRAM transfers data twice during each clock cycle.
DDR memory is available at effective speeds up to 400MHz, which is what you’ll want to get. It’s called both PC3200 and DDR400, depending on where you read it. 400MHz DDR memory actually runs at 200MHz, but it performs data transfers twice per clock cycle. DDR RAM is also available with effective frequencies of 266MHz (PC2100), 333MHz (PC2700), and at higher speeds than 400MHz, but current motherboards don’t support anything higher than 400MHz.
Choosing Memory For the sake of both cost effectiveness and performance, we recommend 400MHz DDR memory. All of the motherboards we recommend use DDR memory, so if you go with one of our recommendations you’ll be prepared for high-speed, extremely efficient memory.
Memory comes on long, thin modules called DIMMs, or Dual Inline Memory Modules. You should buy one 512MB DIMM: motherboards come with a limited number of DIMM slots, so you can keep the extra slots free in case you wish to upgrade down the road. Windows XP and all current games run smoothly with 512MB of memory. With less, Windows tends to swap data to and from its paging file fairly often. More memory may never be used unless you use memory-inten-sive software such as video editors.
Be sure to use name-brand memory, such as that from Corsair, Mushkin, or Viking. Generic memory is often cheap and shoddy, and it won’t allow you to run it as strenuously as name-brand memory. One of our favorite memory vendors, Crucial, isn’t making 400MHz DDR at the time of this writing, though it might be available by the time you read this.
Another specification to look for is the CAS (Column Access Strobe) latency. The higher the latency, the longer memory takes to respond to data requests. Most DDR memory has a CAS latency time of 2.5 cycles. Simplified, this means that after the memory controller has tapped the memory for data from a certain address, it takes two and a half clock cycles for the memory to respond. The lower the CAS latency, the faster the memory.
Depending on your motherboard, you may be able to use the BIOS setup program to “force” the computer to run with a lower CAS latency time, but the PC might become unstable. See “BIOS Tweaking and Overclocking,” later in the chapter.
 This chapter is from Build Your Own High Performance Gamers' Mod PC, by Chen and Durham (McGraw-Hill/Osborne, 2004, ISBN: 0072229012). Check it out at your favorite bookstore today. Buy this book now. |
Next: Installing the Memory Modules >>
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