DRAM Memory Guide
A QUICK REFERENCE TO SYSTEM MEMORY
Often referred to as main memory
RAM is the acronym for Random Access Memory.
It is a type of computer memory that can, as its name implies,
be accessed randomly. That is, any byte of memory can be accessed without
touching the preceding bytes. RAM is the "working memory" storage area within
the computer. All data on the computer is stored on the hard drive, but in order
for the CPU to work with the data during normal operations, the data the computer uses
and works with is read into the working memory, which is the RAM chips.
There are two different types of RAM; DRAM
(Dynamic Random Access Memory) and SRAM
(Static Random Access Memory). The two types
differ in the technology they use to hold data, with DRAM being the more
common type. In terms of speed, SRAM is faster. DRAM needs to be refreshed
thousands of times per second while SRAM does not need to be refreshed,
which is what makes it faster. DRAM supports access times of about 60 nanoseconds,
SRAM can give access times as low as 10 nanoseconds.
Despite SRAM being
faster, it is not as commonly used as DRAM because it is so much more
expensive. Both types of RAM are volatile, meaning that they lose
their contents when the power is turned off.
This reference will provide general information
on the two types of RAM and provide an overview on the common modules of
each type. As DRAM is the main system memory used in home and office PCs,
being cheaper and more common than SRAM, we will focus on DRAM.
|SRAM - Static Random Access Memory
SRAM is short for static random access memory, and pronounced ess-ram. The term static is derived from the fact that it doesn't need to be refreshed
like dynamic RAM. SRAM will retain data in it's memory as long as power is being
supplied. SRAM is faster and more reliable than the more common DRAM.
It is also more expensive than DRAM.
Async SRAM is an older type of SRAM. It is asynchronous, meaning that it
works independently of the system clock.
Pipeline Burst SRAM
Sync SRAM is synchronized with the system clock, and increased speed.
Pipeline Burst SRAM is the most common type of SRAM. It is able to operate
at bus speeds higher than 66MHz.
|DRAM- Dynamic Random Access Memory
DRAM stands for dynamic random access memory, a type of memory used in most
personal computers. Dynamic Random Access Memory must have an electric current
to maintain electrical state (refresh).
FPM DRAM - Fast Page Mode DRAM
EDO DRAM -
Extended Data Out DRAM
FPM DRAM is only slightly faster than regular DRAM. This used to be the
main type of memory used in PCs but was eventually replaced by EDO RAM, due
to its slow speed. FPM DRAM, is now considered to be obsolete. It was mainly
used in the older 386 and 486 computers. It is not suitable for memory buses
over 66 MHz.
EDO DRAM provided a better performance increase over FPM DRAM. EDO RAM
cannot operate on a bus speed faster than 66MHz. With a need for speed,
BEDO DRAM was introduced.
BEDO DRAM - Burst EDO DRAM
SDRAM - Synchronous DRAM
Burst EDO DRAM is a type of EDO DRAM that can process four memory addresses
in one burst. BEDO DRAM can only stay synchronized with the CPU clock for
short periods (bursts). It is faster than it's predecessor, EDO DRAM.
Short for Synchronous DRAM, a type of DRAM that can run at much higher clock
speeds than conventional memory. SDRAM actually synchronizes itself with the
CPU's bus. SDRAM is the new memory standard for modern PCs.
NOTE: When looking at SDRAM The number following "PC" indicates the speed of
the system's frontside bus. (example: The PC100
SDRAM is designed for systems equipped with a 100 MHz frontside
RDRAM - Rambus DRAM
DDR SDRAM - Double Data Rate
Short for Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc.
Whereas the fastest current memory technologies used by PCs (SDRAM) can
deliver data at a maximum speed of about 100 MHz, RDRAM transfers data at up
to 800 MHz. RDRAM (and DDR-SDRAM) are the two technologies expected to
Short for Double Data Rate-Synchronous DRAM, a type of SDRAM that supports
data transfers on both edges of each clock cycle (the rising and falling
edges), effectively doubling the memory chip's data throughput. DDR-SDRAM
also consumes less power, which makes it well-suited to notebook computers.
DDR-SDRAM is also called SDRAM II. and DDRAM. DDR-SDRAM and RDRAM are the
two technologies expected to replace SDRAM.
NOTE: When looking at DDR memory, the number
following "PC" indicates the module's total bandwidth. (example: PC1600 DDR
memory is designed for systems equipped with a 100 MHz frontside bus. The
number 1600' refers to the module's bandwidth; the quantity of data that it
transfers in one second, of 1.6 GB per second.
DDR2 SDRAM is the next step up from DDR SDRAM. DDR2 SDRAM offers new
features and functions that enable higher clock and data rate
operations. DDR2 transfers 64 bits of data twice every clock cycle. DDR2
SDRAM memory is not compatible with current DDR SDRAM memory slots.
SDRAM, RDRAM & DDR/DDR2 SDRAM - A Price
|TYPE OF DRAM
||Average Online Retail
(Dec 2004) *
||PC133 ECC 512-MB
||PC800 ECC 512MB
* Price samples courtesy of
DRAM technology changes and advances quite quickly. Trying to
figure out which type of
you need for an
upgrade can be quite confusing
to the average user. First, you need to know what type of memory is supported by
the system chipset of your
motherboard. This will be indicated on the
documentation/manual included with your motherboard. If this is not available to
you, most motherboard manufactures will have the information available on their
Web site. Additionally, some
Web sites like crucial.com will have a memory selector which allows you to input your
system information into a form and it will return a list of suitable memory
modules you can upgrade with. Unless cost is a major factor, you will want to go with
the fastest type of memory supported by the motherboard. If cost is too much of
an issue you can then look at the next step down and so on until you reach a
happy medium between price and speed.
Due to advances in technology, over and under
production runs, along with rampant competition in the memory retail market,
prices on system memory are constantly fluctuating. A good way to save money or
perhaps to purchase faster memory on a budget is to check memory prices
where there is "worldwide" competition for your upgrade dollars. One site
to help with this task is
PriceWatch here you can search for a
specific type of memory and see the prices hundreds of online vendors are
selling this memory for. Once you have located the vendor with a price that
meets your budget needs, you can then visit
Reseller Ratings, an excellent
website which users customer's experiences to report on the validity of an online
vendor. This combined with watching Weekly Memory Price Guides (such as the one
SharkyExtreme) will help you to better understand memory price trends, so
you can buy the fastest memory supported by your motherboard at a price you
MORE MEMORY TERMINOLOGY
Acronym for single in-line memory module,
circuit board that can hold a group of
chips. A SIMM has a
32-bit path to the
memory chips. Typically, SIMMs hold up to eight (on
Macintoshes) or nine (on
RAM chips. On PCs,
the ninth chip is often used for parity error checking. Unlike memory chips,
SIMMs are measured in
bytes rather than bits. SIMMs are easier to install than individual
memory chips. SIMMs
come in 30-pin and 72-pin varieties.
Short for dual in-line memory module, a
circuit board that holds
chips. A DIMM has a
64-bit path to the memory chips. Because the
Pentium processor requires a 64-bit path to memory you can install
memory one DIMM at a time.
DIMMs come as 168-pin
(SDRAM DIMM) or 184-pin (DDR DIMM)
that is used to provide DDR SDRAM memory
for many desktop computers.
DDR DIMM will not fit into a standard
SDRAM DIMM slot.
The memory module
used with RDRAM
chips. It is similar to a
DIMM package but
uses different pin settings. Rambus trademarked the term RIMM as an
entire word. It is the term used for a module using Rambus technology. It is
sometimes incorrectly used as an acronym for Rambus Inline
Memory Module. RIMMs have
Rambus memory modules will only fit motherboards
and systems especially designed for RIMMs, despite having the same number of
pins as DDR DIMMs.
column address strobe
Abbreviated as CAS, a signal, or strobe, sent by the
to a DRAM circuit to
activate a column address. DRAM stores data in a series of rows and columns,
similar in theory to a spreadsheet, and each cell where a data bit is stored
exists in both a row and a column. A processor uses CAS and
(row address strobe) signals to retrieve data from DRAM. When data is
needed, the processor activates the RAS line to specify the row where the
data is needed, and then activates the CAS line to specify the column.
Combined, the two signals locate the data stored in DRAM.
When seen in memory information, you will
usually spot the reference "CAS2" or "CAS3". The number following CAS (2 or
3)represents the number of clock cycles before a DRAM column can be
accessed. CAS2 or CAS3 are also referred to as CL2 or CL3
To recharge a
device with power or information. For example,
needs to be refreshed
thousands of times per second or it will lose the
stored in it.
(n.) The area of a
that contains slots for
banks are typically double sided (allowing for single- or double-sided
memory modules), and the banks in the slots are numbered. Memory banks are
organized into units representing the minimum number of memory
chips that must
work in tandem.
Short for Error-Correcting Code
memory, a type of
that includes special circuitry for testing the accuracy of
as it passes in and out of memory.
DRAM (dynamic random
computers have access times of 50 to 150
(billionths of a second).
Static RAM (SRAM)
has access times as low as 10 nanoseconds. Ideally, the access time of
memory should be
fast enough to keep up with the
CPU. If not, the CPU
will waste a certain number of clock cycles, which makes it slower.
Refers to physical
memory that is
internal to the
computer. The word main is used to distinguish it from external
devices such as
Another term for main memory is
that hold the data for one
before it is moved on to the
This process increases the reliability of high-speed data access. Registered
memory modules are typically used only in
servers and other
mission-critical systems where it is extremely important that the
contains a buffer to assist the chipset deal with
the large electrical load required
when the system has a lot of memory. Much like
registered modules, buffered
modules are typically used in
servers and other
mission-critical systems where it is extremely important that the
deals directly with the
controller with nothing in
between as they communicate.
modules have an extra chip that will detect if data was
correctly read or written by the memory module. Unlike
ECC, parity will not
correct the error.
Webopedia Memory Category
Webopedia's terms listings and information about computer memory.
Memory Installation Guide
This installation guide will walk you through the steps so
that you can successfully upgrade your memory.
Computer Memory Upgrade (With step-by-step photos)
An install guide on how to add or upgrade computer memory
How To Install Memory
You have new memory for your computer. Now you have to install it. This chapter
will guide you through the basics of memory module installation and refer you to
resources that can help with problems.
SysOpt Article: Are You
Ready For DD2?
Like all worthy technological advancements that move beyond the pushed extremes
of their predecessors, DDR2 memory picks up where DDR leaves off. But instead of
the kowtowing to the industry mantra of “bigger-better-faster,” DDR2 focuses on
small improvements to DDR design that add up to significant performance upgrades
at a lower cost per module.
Hardware Central Tutorials - Memory Packaging
Provides an over view of SIMMs, DIMMs, and Connectors.
What do PC100, PC133, PC1600, PC2100, PC2700 and PC3200 Mean?
An overview on terminology from Packard Bell.
Compare prices between online vendors. This site provides product descriptions,
prices, and shipping costs from many onl;ine vendors in an easy to read chart
ResellerRatings compiles and tracks customer ratings and reviews of popular
Along with providing top-notch hardware reviews, SharkyExtreme offers a
bi-weekly Memory price Guide and a weekly High-end DDR Memory Price Guide.
Rambus RDRAM overview.
Crucial offers over 110,000 upgrades for more than 20,000 desktops, notebooks,
servers, printers, routers, and electronic devices on their Web site.
Additionally they are rated 9.56/10 (by customers) on ResellerRatings.com.
Vangie 'Aurora' Beal -
Last updated: January 14, 2005