Computer Memory
Improve Your PC's
Performance by Adding Memory
By Jean Andrews
Is your PC slow? Does it sometimes give "Out of Memory" errors? Are graphics
slow to display? Does your PC lock up occasionally? All these symptoms might
mean you need more memory. This article discusses the different kinds of memory,
how much memory you need, and how to buy and install it.
How Much Memory is Enough?
If
you have a Pentium system with less than 32 MB of memory, adding memory might
make a real difference in overall performance. Most of today's Pentium systems
can benefit from 128 MB of memory and more. However, Pentium systems using
Windows 95 or Windows 98 can make better use of memory than older 486 systems
using DOS and Windows 3.x. So, when attempting to improve system performance, if
you have an older system, upgrading the CPU or even the entire system board
might be the best solution.
Different Types of Memory
There are two general categories of memory, static RAM (random access memory)
and dynamic RAM, and the CPU uses each differently. Static RAM (SRAM, pronounced
"S-ram") holds its data as long as the power is on, but dynamic RAM (DRAM,
"D-ram") can only hold data for a few milliseconds, so must be constantly
refreshed, which makes it slower than the more expensive SRAM. A system will
have a little SRAM to improve system performance, and use a lot of DRAM to keep
cost down. Most systems come with an optimum amount of SRAM already installed,
but have plenty of room for additional DRAM.
DRAM comes on two kinds of tiny boards, either a SIMM or a DIMM, that install in
memory slots on the system board called memory banks. SIMMs are installed in
pairs and DIMMs are installed as single units. A system board can support only
certain amounts of one or the other. Older system boards had just SIMM slots.
Then, when DIMMs were introduced, boards offered some SIMM slots and some DIMM
slots. All the newest system boards have just DIMM slots.
Before You Buy
Your system board already has some SIMMs or DIMMs installed, so here's what you
need to know before buying memory:
-
How much memory
is already installed? (For example, 8 MB, 16 MB or 64 MB)
-
How many DIMM
or SIMM slots are on the board and how many of these slots are empty?
-
What size and
type DIMM or SIMM can the board support?
The answer to Question 1 above is easy to find. Boot up your PC and watch the
system count up memory before Windows loads. If you miss the count, you can
either check CMOS setup or you can let Windows tell you. Right-click on the My
Computer icon on your Windows desktop. Select Properties from the drop-down menu
and click the General tab. The amount of memory that Windows recognizes as
installed is written at the bottom of this window.
The answer to Question 2 is a little more difficult to find. Turn off the PC,
unplug it and open the computer case. Don't touch anything inside the case so as
not to damage chips with static electricity. Note how many SIMM or DIMM slots
are empty and how many are used.
You'll need the system board documentation to answer Question 3. For systems
that use SIMMs, look for a table of the different sizes of SIMM modules the
board supports. You can have a combination of more than one size, but each SIMM
in a pair must be the same size and speed. For DIMMs, look in the documentation
for the different sizes the board can use. You can mix DIMMs of different sizes
on a board.
Now that you know how many and what size of SIMMs or DIMMs to buy, the next step
is to determine what type. Memory technology has improved over the years and
each technology is a little faster than the previous ones. For SIMMs, your
system probably uses EDO, but some older systems might use FPM and a very few
use BEDO. DIMMs on a 100 MHz system board will be Synchronous DRAM (SDRAM), but
older, slower system boards might use EDO or BEDO DIMMs. Two up-and-coming
memory technologies are Direct Rambus DRAM and Double Data Rate SDRAM. If your
system board is the latest and greatest, it might use one of these types.
The speed of a memory module is measured in nanoseconds except for SDRAM, which
is rated by the system board speed (rather than memory speed), and is most
likely 100 MHz. A DIMM uses either 3.3 or 5 volts and is either buffered or
unbuffered. The two notches on a DIMM are positioned differently so you can't
insert the wrong type module in a slot. Some DIMMs support error checking and
correction (ECC) technology. SIMMs can use either parity (checks for bad bits)
or non-parity (does not check). Most systems use non-parity memory because it's
less expensive. Check your system board documentation for the type memory it
supports.
When You Buy
When buying SIMMs and DIMMs, pay close attention to what type of memory you're
buying as well as the speed and size of the module. If you have questions, bring
the system board documentation with you when buying. Also, be sure you
understand the store's return policy and guarantee.
Memory prices
were at an all-time low last summer, but because of economic conditions in Asia
as well as the earthquake in Taiwan, they have climbed. According to Jim Cheng,
owner of GIMM Computers, a computer parts store in Atlanta, memory prices peaked
in September and October. The prices have steadily dropped since then, and Mr.
Cheng says he expects they will continue to drop until about February or March,
but most likely will never reach the rock-bottom prices of last June.
Installing Memory
Installing memory in a PC is very easy, but you must be very careful to protect
the memory and other chips inside the computer against static electricity, which
can totally fry a chip. In fact, you can touch a SIMM or DIMM and static
electricity on your body can totally destroy the module or, worse yet, just make
it unreliable, but you never felt a thing! So, as you work, use a static
electricity bracelet that's properly grounded. Follow these simple steps to
install memory:
-
Turn the PC off
and unplug it.
-
Remove the
computer case.
-
Locate the
memory slot and open the supporting arms on both ends of the slot.
-
For a SIMM,
place each module in its slot at a 45-degree angle and then gently snap it in
place.
-
For a DIMM,
insert the module straight down into the slot until it snaps in place.
-
Replace the
case cover, plug in the power and turn on the PC.
-
Enter CMOS
setup and verify that the setup program recognizes the correct amount of
memory, and then reboot into Windows.
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