Not sure what memory to buy?
The most important thing to ensure when buying memory is
compatibility with your system. In addition, you'll need to decide how much
memory you need and beyond that lie considerations of price, quality,
availability, service, and warranty. This section helps you address these
important decision factors and helps you answer questions like these:
·
How
much memory do I need?
·
How
much memory will my system recognize?
·
What
kind of memory is compatible with my system?
·
How
many sockets are open and how should I fill them?
·
How
do I determine the quality of memory?
·
What
should I know about memory prices?
·
What
other issues should I consider?
COMPATIBILITY
Compatibility of memory components with your computer system is
arguably the most important factor to consider when upgrading memory. This
section can get you started.
WHAT KIND OF MEMORY IS
COMPATIBLE WITH MY SYSTEM?
The easiest way to determine what type of memory goes with your
system is to consult with your system documentation. In most cases, the manual
will provide basic specifications such as the speed and technology of the
memory you need. This information is usually enough to choose a module by
specification. If you don't feel you have enough information, you can call your
system manufacturer's toll-free technical support number for assistance.
HOW MANY SOCKETS DO I HAVE
OPEN?
You may or may not have an idea what the inside of your computer
looks like and how memory is configured. You may have opened up your computer
when you bought it to see the configuration inside, or you may have looked at a
configuration diagram in your user's manual. Even if
you have no idea of the memory configuration of your system, you can use
Non-removable memory usually comes in the form of memory chips
soldered directly onto the system board. It is represented in the bank schema
in brackets: [_4MB_] indicates 4MB of non-removable memory soldered onto the
board and two available memory sockets.
You can find out how many sockets are in the system and how many
are filled by pressing the F1 key during system startup. If your system
supports this, a screen will appear that indicates how many memory sockets are
in the system, which ones are filled and which are open, and what capacity
modules are in each socket. If pressing the F1 key during startup doesn't
produce this result, check your computer's system manual for more information.
As a last resort, you can open your computer and take a look at the
sockets. (Important Note: Before removing the cover of your computer, refer to
the computer's system manual and warranty information for instructions and
other relevant information.) If you do open the computer, you may be able to
identify "bank labels" that indicate whether memory are installed in
pairs. Bank numbering typically begins with 0 instead of 1. So, if you have two
banks, the first bank will be labeled "bank 0", and the second bank
will be labeled "bank 1."
HOW SHOULD I FILL THE
SOCKETS?
In most cases, it's best to plan your memory upgrade so you won't
have to remove and discard the memory that came with the computer. The best way
to manage this is to consider the memory configuration when you first buy the
computer. Because lower-capacity modules are less expensive and more readily
available, system manufacturers may achieve a base configuration by filling
more sockets with lower-capacity modules. By way of illustration, consider this
scenario: a computer system with 64MB standard memory comes with either two (2)
32MB modules or one (1) 64MB module. In this case, the second configuration is
the better choice because it leaves more room for growth and reduces the chance
that you'll have to remove and discard lower-capacity modules later. Unless you
insist on the (1) 64MB module configuration, you may find yourself with only
one socket left open for upgrading later.
Once you have purchased a computer and are planning your first
upgrade, plan to buy the highest-capacity module you think you may need,
especially if you only have one or two sockets available for upgrading. Keep in
mind that, in general, minimum memory requirements for software applications
double every 12 to 18 months, so a memory configuration that's considered large
today will seem much less so a year from now.
DIFFERENT KINDS OF MEMORY
Some people like to know a lot about the computer systems they own
- or are considering buying - just becauuse. They're like that. It's what makes
them tick. Some people never find out about their systems and like it that way.
Still other people - most of us, in fact - find out about their systems when
they have to - when something goes wrong, or when they want to upgrade it. It's
important to note that making a choice about a computer system - and its memory
features - will affect the experience and satisfaction you derive from the system.
This chapter is here to make you smarter about memory so that you can get more
out of the system you're purchasing or upgrading.
MODULE FORM FACTORS
The easiest way to categorize memory is by form factor. The form factor of any memory module describes its
size and pin configuration. Most computer systems have memory sockets that can
accept only one form factor. Some computer systems are designed with more than
one type of memory socket, allowing a choice between two or more form factors.
Such designs are usually a result of transitional periods in the industry when
it's not clear which form factors will gain predominance or be more available.
SIMMS
As previously mentioned, the term SIMM stands for Single
In-Line Memory Module. With SIMMs, memory chips are soldered onto a modular
printed circuit board (PCB), which inserts into a socket on the system board.
The first SIMMs transferred 8 bits of data at a time. Later, as
CPUs began to read data in 32-bit chunks, a wider SIMM was developed, which
could supply 32 bits of data at a time. The easiest way to differentiate
between these two different kinds of SIMMs was by the number of pins, or
connectors. The earlier modules had 30 pins and the later modules had 72 pins.
Thus, they became commonly referred to as 30-pin SIMMs and 72-pin SIMMs.
Another important difference between 30-pin and 72-pin SIMMs is
that 72-pin SIMMs are 3/4 of an inch (about 1.9 centimeters) longer than the
30-pin SIMMs and have a notch in the lower middle of the PCB. The graphic below
compares the two types of SIMMs and indicates their data widths.
DIMMS
Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs.
Like SIMMs, most DIMMs install vertically into
expansion sockets. The principal difference between the two is that on a SIMM,
pins on opposite sides of the board are "tied together" to form one
electrical contact; on a DIMM, opposing pins remain electrically isolated to
form two separate contacts.
168-pin DIMMs transfer 64 bits of data at
a time and are typically used in computer configurations that support a 64-bit
or wider memory bus. Some of the physical differences between 168-pin DIMMs and 72-pin SIMMs include: the length of module, the
number of notches on the module, and the way the module installs in the socket.
Another difference is that many 72-pin SIMMs install
at a slight angle, whereas 168-pin DIMMs install
straight into the memory socket and remain completely vertical in relation to
the system motherboard. The illustration below compares a 168-pin DIMM to a
72-pin SIMM.
SO DIMMS
A type of memory commonly used in notebook computers is called SO
DIMM or Small Outline DIMM. The principal difference between a SO DIMM and a
DIMM is that the SO DIMM, because it is intended for use in notebook computers,
is significantly smaller than the standard DIMM. The 72-pin SO DIMM is 32 bits
wide and the 144-pin SO DIMM is 64 bits wide.
RIMMS AND SO-RIMMS
RIMM is the trademarked name for a Direct Rambus memory module. RIMMs look
similar to DIMMs, but have a different pin count. RIMMs transfer data in 16-bit chunks. The faster access and
transfer speed generates more heat. An aluminum sheath, called a heat spreader, covers the module to
protect the chips from overheating.
FLASH MEMORY
Flash memory is a solid-state, non-volatile, rewritable memory that functions
like RAM and a hard disk drive combined. Flash memory stores bits of electronic
data in memory cells, just like DRAM, but it also works like a hard-disk drive
in that when the power is turned off, the data remains in memory. Because of
its high speed, durability, and low voltage requirements, flash memory is ideal
for use in many applications - such as digital cameras, cell phones, printers,
handheld computers, pagers, and audio recorders.
PC CARD AND CREDIT CARD
MEMORY
Before SO DIMMs became popular, most
notebook memory was developed using proprietary designs. It is always more
cost-effective for a system manufacturer to use standard components, and at one
point, it became popular to use the same "credit card" like packaging
for memory that is used on PC Cards today. Because the modules looked like PC
Cards, many people thought the memory cards were the same as PC Cards, and
could fit into PC Card slots. At the time, this memory was described as
"Credit Card Memory" because the form factor was the approximate size
of a credit card. Because of its compact form factor, credit card memory was
ideal for notebook applications where space is limited.
PC Cards use an input/output protocol that used to be referred to
as PCMCIA (Personal Computer Memory Card International Association). This
standard is designed for attaching input/output devices such as network
adapters, fax/modems, or hard drives to notebook computers. Because PC Card
memory resembles the types of cards designed for use in a notebook computer's
PC Card slot, some people have mistakenly thought that the memory modules could
be used in the PC Card slot. To date, RAM has not been packaged on a PCMCIA
card because the technology doesn't allow the processor to communicate quickly
enough with memory. Currently, the most common type of memory on PC Card
modules is Flash memory.
MAJOR CHIP TECHNOLOGIES
It's usually pretty easy to tell memory module form factors apart
because of physical differences. Most module form factors can support various
memory technologies so, it's possible for two modules to appear to be the same
when, in fact, they're not. For example, a 168-pin
DIMM can be used for
FAST PAGE MODE (FPM)
At one time, FPM was the most common form of DRAM found in
computers. In fact, it was so common that people simply called it
"DRAM," leaving off the "FPM". FPM offered an advantage
over earlier memory technologies because it enabled faster access to data
located within the same row.
EXTENDED DATA OUT (
In 1995,
SYNCHRONOUS DRAM (SDRAM)
In late 1996, SDRAM began to appear in systems. Unlike previous
technologies, SDRAM is designed to synchronize itself with the timing of the CPU.
This enables the memory controller to know the exact clock cycle when the
requested data will be ready, so the CPU no longer has to wait between memory
accesses. SDRAM chips also take advantage of interleaving and burst mode
functions, which make memory retrieval even faster. SDRAM modules come in
several different speeds so as to synchronize to the clock speeds of the
systems they'll be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM
runs at 100MHz, PC133 SDRAM runs at 133MHz, and so on. Faster SDRAM speeds such
as 200MHz and 266MHz are currently in development.
DOUBLE DATA RATE SYNCHRONOUS
DRAM (DDR SDRAM)
DDR SDRAM, is a next-generation SDRAM
technology. It allows the memory chip to perform transactions on both the
rising and falling edges of the clock cycle. For example, with DDR SDRAM, a 100
or 133MHz memory bus clock rate yields an effective data rate of 200MHz or
266MHz. Systems using DDR SDRAM are expected to ship at the end of the year
2000.
DIRECT RAMBUS
Direct Rambus is a new DRAM architecture
and interface standard that challenges traditional main memory designs. Direct Rambus technology is extraordinarily fast compared to older
memory technologies. It transfers data at speeds up to 800MHz over a narrow
16-bit bus called a Direct Rambus Channel. This high-speed clock rate is possible
due to a feature called "double clocked," which allows operations to
occur on both the rising and falling edges of the clock cycle. Also, each
memory device on an RDRAM module provides up to 1.6 gigabytes per second of
bandwidth - twice the bandwidth available with current 100MHz SDRAM.
In addition to chip technologies designed for use in main memory,
there are also specialty memory technologies that have been developed for video
applications.
MEMORY TECHNOLOGIES FOR
VIDEO OR GRAPHICS PROCESSING
VIDEO RAM (VRAM)
VRAM is a video version of FPM technology. VRAM typically has two
ports instead of one, which allows the memory to allocate one channel to
refreshing the screen while the other is focused on changing the images on the
screen. This works much more efficiently than regular DRAM when it comes to
video applications. However, since video memory chips are used in much lower
quantities than main memory chips, they tend to be more expensive. So, a system
designer may choose to use regular DRAM in a video subsystem, depending on
whether cost or performance is the design objective.
WINDOW RAM (WRAM)
WRAM is another type of dual-ported memory also used in
graphics-intensive systems. It differs slightly from VRAM in that its dedicated
display port is smaller and it supports
SYNCHRONOUS GRAPHICS RAM
(SGRAM)
SGRAM is a video-specific extension of SDRAM that includes
graphics-specific read/write features. SGRAM also allows data to be retrieved
and modified in blocks, instead of individually. This reduces the number of
reads and writes that memory must perform and increases the performance of the
graphics controller by making the process more efficient.
BASE RAMBUS AND CONCURRENT
RAMBUS
Before it even became a contender for main memory, Rambus technology was actually used in video memory. The
current Rambus main memory technology is called
Direct Rambus. Two earlier forms of Rambus are Base Rambus and
Concurrent Rambus. These forms of Rambus
have been used in specialty video applications in some workstations and video
game systems like Nintendo 64 for several years.
HOW MUCH MEMORY DO YOU NEED?
Perhaps you already know what it's like to work on a computer that
doesn't have quite enough memory. You can hear the hard drive operating more
frequently and the "hour glass" or "wrist watch" cursor
symbol appears on the screen for longer periods of time. Things can run more
slowly at times, memory errors can occur more frequently, and sometimes you can't
launch an application or a file without first closing or quitting another.
So, how do you determine if you have enough memory, or if you would
benefit from more? And if you do need more, how much more?
The fact is, the right amount of memory depends on the
type of system you have, the type of work you're doing, and the software
applications you're using. Because the right amount of memory is likely to be
different for a desktop computer than for a server, we've divided this section
into two parts - one for each type of system.
MEMORY REQUIREMENTS FOR A
DESKTOP COMPUTER
If you're using a desktop computer, memory requirements depend on
the computer's operating system and the application software you're using.
Today's word processing and spreadsheet applications require as little as 32MB
of memory to run. However, software and operating system developers continue to
extend the capabilities of their products, which usually means
greater memory requirements. Today, developers typically assume a minimum memory
configuration of 64MB. Systems used for graphic arts, publishing, and
multimedia call for at least 128MB of memory and it's common for such systems
to require 256MB or more for best performance.
INSTALLING MEMORY
Before you start, make sure you have the following:
Your computer manual. To install memory, you must open the
computer box (chassis) and locate the memory sockets. You may need to unplug
cables and peripherals, and re-install them afterward. The manual will most
likely provide instructions specific to your computer.
A small screwdriver. Most computer chassis assemble with
screws. The screwdriver also comes in handy if the notches on memory sockets
are too tiny for your fingers.
IMPORTANT THINGS TO KEEP IN
MIND
ESD DAMAGE
Electro-Static Discharge (ESD) is a frequent causes
of damage to the memory module. ESD is the result of handling the module
without first properly grounding yourself and thereby dissipating static
electricity from your body or clothing. If you have a grounded wrist strap,
wear it. If you don't, before touching electronic components - especially your
new memory module - make sure you first touch an unpainted, grounded metal
object. Most convenient is the metal frame inside the computer. In addition,
always handle the module by the edges. If ESD damages memory, problems may not
show up immediately and may be difficult to diagnose. Wearing a grounded wrist
strap can prevent ESD damage.
SWITCHING OFF THE POWER
Before opening the chassis, always power-off your computer and all
attached peripherals. Leaving power on can cause permanent electrical damage to
your computer and its components.
INSTALLING THE MEMORY
The vast majority of computers today have memory sockets that
accept the following industry-standard memory modules:
Desktops, Workstations and Servers
·
72-pin
SIMM
·
168-pin
DIMM
·
184-pin
RIMM
Notebooks and
·
144-pin
SO DIMM
Although sockets may be in different places on different computers,
installation is the same. Consult the computer owner's manual to find out
whether the memory sits on an expansion card or on the motherboard, and whether
internal computer components must be moved to gain access.
In the section below are installation instructions for the standard
modules listed above, followed by installation instructions for some of the
more popular proprietary memory modules. If the computer requires proprietary
memory, or the instructions below don't seem to apply to your situation, phone
Kingston Technology's Technical Support Group at (800) 435-0640.
INSTALLING A 72-PIN SIMM
Place your computer's power switch in the off position and
disconnect the AC power cord.
Follow the instructions in your owner's manual that describe how to
locate your computer's memory expansion sockets.
Before touching any electronic components or opening the package
containing your new module(s), make sure you first touch an unpainted, grounded
metal object to discharge any static electricity you may have stored on your
body or clothing.
Handle your new module(s) carefully; do not flex or bend the
module(s). Always grasp the module by its edges.
As shown in the illustration, the module and the expansion socket
are keyed. A small plastic bridge in the socket must align with the curved
notch in the module. The bridge ensures the module can only be plugged into the
socket one way.
Insert the module into the socket at a slight angle. Make sure the
module is completely seated in the socket. If you're having problems inserting
the module into the socket, stop and examine both the module and the socket;
make sure the notch in the module is properly aligned with the keyed plastic
bridge in the socket. Do not force the module into the socket. If too much
force is used, both the socket and module could be damaged.
Once you are satisfied the module is seated properly in the socket,
rotate the module upward until the clips at each end of the expansion socket
click into place.
After all modules have been installed, close the computer, plug in
the AC power cord, and reinstall any other cables that may have been
disconnected during the installation process.
INSTALLING A 168-PIN DIMM
Locate the memory expansion sockets on the computer's motherboard. If all the
sockets are full, you will need to remove smaller capacity modules to allow
room for higher capacity modules.
For some installations, DIMM memory can be installed in any
available expansion slot. Other installations may require the memory to be
installed in a particular sequence based on the module's capacity. Check your
owner's manual to determine the correct installation sequence for your
configuration.
Insert the module into an available expansion socket as shown in
the illustration. Note how the module is keyed to the socket. This ensures the
module can be plugged into the socket one way only. Firmly press the module
into position, making certain the module is completely seated in the socket.
Repeat this procedure for any additional modules you are installing.
Most 168-pin DIMM modules have ejector tabs similar to those shown
in the illustration. The ejector tabs are used only when you need to remove a
module. By pressing down on the ejector tabs, the module will pop up from the
socket and it can be removed.
INSTALLING A 184-PIN RIMM
Turn off the computer and disconnect the AC power cord.
Locate your computer's memory expansion sockets by following the
instructions in your owner's manual.
Before touching any electronic components, make sure you first
touch an unpainted, grounded metal object to discharge any static electricity
stored on your clothing or body.
If all the sockets are full, you will need to remove smaller
capacity modules to allow room for higher capacity modules.
The ejector tabs shown in the illustration are used to remove a
module. By pushing outward on the ejector tabs, the module will pop up from the
socket and it can then be removed.
For most installations, Rambus modules
can be installed in any available expansion socket, but any empty sockets must
contain a continuity module as shown in the illustration. Note that some modes
may use a specific installation sequence for Rambus
modules (e.g. Rambus dual-channel configurations);
see your owner's manual for more details.
Insert the module into an available expansion socket as shown in
the illustration. Note how the module is keyed to the socket. This ensures the
module can be plugged into the socket one way only. Firmly press the module
into position, making certain the module is completely seated in the socket.
The ejector tabs at each end of the socket will automatically snap into the
locked position. Repeat this procedure for any additional modules are
installing.
Once the module or modules have been installed, close the computer.