RAM
RA
MBUYERS GUIDE
40 MA XIMUMPC OCTOBER 2005
COMMON QUESTIONS AND ANSWERS
DDR2 RAM uses a ball-grid array to mount
the chip to the DIMM for better performance.Many early P4 machines used RDRAM,
which has all but been abandoned.How much should you add?
W
hen it comes to adding memory, more
is (usually) better. But how much more
do you need? Here are some basic guide-
lines:
Ñ If you have 256MB or less, upgrade
your RAM to at least 512MB, no matter what
you’re doing. Even if you don’t use “power
apps” such as imaging, video editing, or
heavy 3D gaming, having more memory is
benefi cial because you can have multiple
programs and web browser windows open
without slowing your system to a crawl.
Ñ For a more precise way to calculate
how much RAM you need in your work, try
this: Load your typical applications and data
fi les, then press Ctrl-Alt-Del to bring up the
Task Manager, and click the Performance
tab. Take a look at fi gures for Commit
Charge and Physical Memory. If Commit
Charge is consistently larger than Total
Memory, you could use a memory upgrade.
Ñ If you’re using video or photo-editing
programs, 3D modeling programs, or enjoy
the latest 3D games such as Doom 3 , you
should have at least 1GB of RAM, and
more is even better. See the “Benchmarks”
sidebar on the next page for details.ADDING MEMORY
Q
What is the signifi cance of the
numbers listed after the model
number for a module, such as 3-4-4-8?A
The fi rst number is the CAS latency
(CL), which is the number of clock
cycles between the time a read command is
sent and the data is available. The second
number is the tRCD (row address to column
address delay), which is the number of clock
cycles between the active command and the
read or write command. The third number
is the tRP (row precharge time), which is the
number of clock cycles between a precharge
command and the active command. The
fourth number is the tRAS (row active time),
the number of clock cycles between a
bank active command and a bank recharge
command. The standard values for a
memory module are stored in its SPD (serial
presence detect) chip, and are used by the
BIOS when you select “By SPD” or “Auto”
for memory timings.Q Can I change these values?
A
Most systems permit you to
manipulate memory timings.
Reducing the tRCD and tRP values can
improve memory performance, although
you might need to increase the CL value a
bit to maintain stability.Q
Is there really a performance
difference between generic,
branded, and premium RAM?A
Differences in performance between
generic, branded, and premium
RAM are not always easy to quantify.
Generally, generic RAM has higher (slower)
memory timing than other types, so it’s
not as adaptable to nonstandard settings.
Branded RAM is likely to have lower
(faster) memory timings than generic RAM,
but its memory timings are usually not as
fast as premium RAM. The best premium
RAM provides very low memory timings
for very fast performance at standard and
overclocked settings.Q
Is it worth the extra expense to
buy overclockable memory if I
don’t intend to overclock it?A
There’s no need to spend the
money on memory designed
for overclocking unless you plan to
overclock it. However, if you’ve had
system lockups after your computer has
been turned on for a long time, you might
be experiencing memory overheating.One of the benefi ts of overclock-friendly
memory versus standard memory is the
presence of heat spreaders (metal plates
over the memory to help dissipate heat).
Using memory with heat spreaders can
help reduce overheating and improve
system stability. You don’t need to buy
new memory, though; you can buy heat
spreaders for existing memory from
many vendors.Q
Do I need ECC RAM if I don’t
have an ECC mobo?A
ECC (error correcting code) RAM
is very valuable if you’re running a
server: It detects and corrects single-bit
memory errors. But ECC features work
only if your motherboard supports ECC
memory. Most motherboards and PC
chipsets ignore ECC memory, so unless
your system can use it, save your money
(ECC costs more than standard memory).Q
If I want to add to the memory
already in my system, do I need to
match the exact brand and type?A
It’s not necessary unless you have a
dual-channel system and you don’t
have a matched pair of modules already
installed. In that case, you should use
a program such as SiSoftware Sandra
2005 Lite to fi nd out the size, speed,
and memory timings of your existing
module and buy a module that matches.
If you match memory and timing, brand
is unimportant. Then, install the old and
new module in the right slots to enable
dual-channel memory access. See your
motherboard manual for details.Q
When I add memory to my
system, what are the most
important specs to look for?A
SPEED (PC or PC2 rating). This
should be the same or faster than
your existing memory.SIZE. For a single-channel system,
buy the largest (in MB) module you can
afford. For a dual-channel system, buy
a matched set of modules providing the
total size you need. For example, two
512MB modules will run faster than a 1GB
module on a dual-channel system. If you’re
upgrading a laptop, you usually only have
one memory slot, so fi ll it with the biggest
module available.
TIMINGS. If you’re a hardcore gamer,
you’ll probably want to overclock your
memory. Look for low-latency memory,
and remember to consider all the numbers,
not just the CAS latency value.