MaximumPC 2005 10

RAM TODAY’S WAY

Kingston’s HyperX memory features

low latencies and blue heat spreaders

marked with the famous “red head”

Kingston logo and. http://www.kingston.com

OCZ EL Titanium modules feature tita-

nium-plated copper heat spreaders, low

latencies, overvoltage protection, noise

reduction, and capacities of 512MB and

1GB in both DDR and DDR2 varieties.

http://www.ocztechnology.com

UNDERSTAND YOUR RAM

RAM stands for “random access

memory.” Your computer uses RAM

as a temporary workspace. The CPU

transfers data and applications from

long-term storage devices (your hard

drive and optical drive) into RAM, then

runs the programs and accesses data

from memory. New data is created within

your system memory before it’s ever

saved to a storage device. Every byte

of information used by a PC during its

operation fl ows through RAM on its way

to or from an I/O device, the CPU, or a

storage device.

Access to data in RAM is immediate:

The CPU can read or write to any

location in memory without having to

muddle through the adjoining data.

Most RAM used in PCs today is

dynamic RAM, or DRAM. It’s called

“dynamic” because the memory chips

must receive new electrical charges (a

process known as memory refreshing)

thousands of times a second, or the data

stored in the chips is lost. This is why

information saved only in RAM is lost as

soon as your PC is restarted or turned off.

RAM AND PAGING FILES

If a program or data fi le is too large to

completely reside in RAM, PCs use

dedicated areas of the hard disk to store

the overfl ow. This dedicated disk space

is known as “virtual memory.” The paging

fi le (swapfi le) in Windows is an example of

virtual memory. Windows uses the paging

fi le as a holding tank for information being

transferred in and out of your system RAM.

The less RAM you have, the more frequently

your paging fi le is used.

Although a paging fi le enables a system

with a relatively small amount of memory to

work with fi les that exceed the amount of

available physical memory, using the paging

fi le instead of physical memory has a huge

negative impact on performance. Hard

drives move data an order of magnitude

slower than even the slowest RAM.

This means that the more memory you

add to your system, the greater the number

of programs you can run, and your system

can work with larger fi les before resorting

to the paging fi le. In an ideal situation, the

paging fi le would never be used. In practical

terms, you want to install enough memory to

handle the largest amount of work (or play)

your PC performs on a routine basis. Check

out our benchmarks on page 41 to see how

different amounts of RAM can affect system

performance in applications and games.

There are two types of RAM used in

today’s PCs: DDR (double data-rate)

and DDR2 (second-generation DDR).

These memory types are usually

synchronized to the processor’s

front-side bus (FSB) speed, as was

their ancestor, SDRAM memory.

Both DDR and DDR2 provide faster

performance than SDRAM because

they run at much higher clock speeds,

and transfer twice the amount of data

every clock cycle as vanilla SDRAM

was capable of. Despite the similar

names, DDR and DDR2 are not

compatible with each other and cannot

be interchanged.

UNDERSTANDING DDR

NOMENCLATURE

The naming scheme for DDR memory can

be very confusing. How do you know if you

have DDR400, 200MHz DDR memory, or

PC3200 DDR SDRAM? The trick is, it’s all

the same memory. Because DDR400 runs

at a clock speed of 200MHz but makes

two reads or writes per clock cycle, the

effective speed of the memory is 400MHz.

People also refer to DDR memory by its

throughput. For example, DDR400 memory

has a maximum throughput of 3,200MB/s,

so memory modules using DDR400 RAM

are also called PC3200 modules. The most

common DDR memory speeds are shown

in Table 1 on the following page. Speeds

above PC4000 are used primarily by

extremely high-performance, overclocked

systems.

Aside from the PC rating, the other

factor that’s important when you select

DDR memory is the rated CAS (column,

address, strobe) latency. CAS latency

(often abbreviated as CL) refers to

the number of clock cycles needed to

access the memory. Most DDR memory

has a CL rating of 2.5 or 3. Lower-

latency modules running at the same

clock speed as higher-latency modules

provide faster memory access.

OCTOBER 2005 MA XIMUMPC 

PHOTOGRAPHY BY MARK MADEO

Mushkin Extreme Performance DDR

modules include a black six-layer

PCB, integrated heat spreaders, and

very low latencies. http://www.mushkin.com