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Computer Memory Types
SRAM
Static random access memory ram uses multiple transistors, typically four to
six, for each memory cell but doesn't have a capacitor in each cell. It is used
primarily for cache.
DRAM
Dynamic random access memory ram has memory cells with a paired transistor
and capacitor requiring constant refreshing.
FPM DRAM
Fast page mode dynamic random access memory was the original form of
DRAM. It waits through the entire process of locating a bit of data by column
and row and then reading the bit before it starts on the next bit. Maximum
transfer rate to L2 cache is approximately 176 megabytes per second.
EDO DRAM
Extended data-out dynamic random access memory does not wait for all of
the processing of the first bit before continuing to the next one. As soon as
the address of the first bit is located, EDO DRAM begins looking for the next
bit. It is about five percent faster than FPM. Maximum transfer rate to L2 cache
is approximately 264 megabytes per second.
SDRAM
Synchronous dynamic random access memory takes advantage of the burst
mode concept to greatly improve performance. It does this by staying on the row
containing the requested bit and moving rapidly through the columns, reading
each bit as it goes. The idea is that most of the time the data needed by the
CPU will be in sequence. SDRAM is about five percent faster than EDO RAM and is
the most common form in desktops today. Maximum transfer rate to L2 cache is
approximately 528 megabytes per second.
RDRAM
Rambus dynamic random access memory is a radical departure from the
previous DRAM architecture. Designed by Rambus,
RDRAM uses a Rambus in-line memory module (RIMM), which is similar in
size and pin configuration to a standard DIMM. What makes RDRAM so different is
its use of a special high-speed data bus called the Rambus channel. RDRAM memory
chips work in parallel to achieve a data rate of 800 MHz.
Credit Card Memory
Credit card memory is a proprietary self-contained DRAM memory module that plugs
into a special slot for use in notebook
computers.
PCMCIA Memory Card
Another self-contained DRAM module for notebooks, cards of this type are not
proprietary and should work with any notebook computer whose system bus matches
the memory card's configuration.
FlashRAM
FlashRAM is a generic term for the small amount of memory used by devices like TVs,
VCRs and car
radios to maintain custom information. Even when these items are turned off,
they draw a tiny amount of power to refresh the contents of their memory. This
is why every time the power flickers, the VCR blinks 12:00. It's also why you
lose all presets on your radio when your car battery dies! Your computer has
FlashRAM to remember things like hard disk settings -- see this
Question of the Day for details.
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VRAM
VideoRAM, also known as multiport dynamic random access memory (MPDRAM),
is a type of RAM used specifically for video
adapters or 3-D accelerators. The "multiport" part comes from the
fact that VRAM normally has both random access memory and serial access memory.
VRAM is located on the graphics card and comes in a variety of formats, many of
which are proprietary. The amount of VRAM is a determining factor in the resolution
and color depth of the
display. VRAM is also used to hold graphics-specific information such as 3-D
geometry data and texture maps. |
SDR
SDRAM vs DDR
SDRAM
The conventional SDRAM modules and DDR
SDRAM modules have the same basic lines, as can be seen in this picture. It is
still difficult for the uninitiated to spot the difference between the two
DIMM's. SDRAM (above) has two notches, whereas DDR SDRAM (below) only has one.
If you have an MSI Pro266 Master or a Shuttle AV32, it's a good idea to take a
good look at your board slots. Both boards have SDR DIMM slots and DDR DIMM
slots. It's easy to confuse the two if you don't pay close attention to the
notches.
To use DDR memory, your system has to
specifically support the technology. Typically PCs will support DDR RAM, but
don't assume that all will. Check with your computer maker to ensure that the
motherboard supports DDR RAM.
When buying DDR SDRAM you'll be faced with a choice of two types. (This is all
so complicated isn't it?) They are PC1600 or PC2100.
While your motherboard may support DDR memory, you will need to check to see
that it supports PC2100 DDR SDRAM. Some early models of DDR-enabled motherboards
only work with PC1600. You also need to ensure that the processor for your
computer can support PC2100.
PC1600 DDR is designed for motherboards and processors with a 200
MHz bus and PC2100 DDR is designed for a motherboards and processors with
a 266 MHz bus. Remember that the bus is all those circuits on the
motherboard that moves data around. They are kind of like data highways that run
between the processor and RAM and all the other components in a computer.
DDR3
DDR3 is Double Data Rate
(DDR) Synchronous Dynamic Random Access Memory (SDRAM). DDR3
memory modules. They are an improvement over DDR and DDR2 memory
technology and deliver higher clock frequencies, lower
power consumption and as a result lower heat dissipation.
DDR3 comes in different frequencies, 1066Mhz and 1333Mhz,
with 1600MHz and beyond coming down the pike.DDR3 modules use just 1.5V,
compared to DDR2's 1.8V and DDR's 2.5V. It seems that many of
the 1066MHz and 1333MHz DDR3 modules will need 1.7V to operate
at those frequencies, which is still much lower than what we are
seeing DDR2 using at the same frequencies. With enthusiast and
gamer oriented DDR3 modules starting off at 1333MHz and will continue to
increase from 1.7V.
Memory Table
| DDR1 |
PC2100 |
DDR266 |
| DDR1 |
PC2700 |
DDR333 |
| DDR1 |
PC3200 |
DDR400 |
| DDR2 |
PC4200 |
DDR533 |
| DDR2 |
PC5300 |
DDR667 |
| DDR2 |
PC6400 |
DDR800 |
| DDR3 |
PC8500 |
DDR1066 |
| DDR3 |
PC10600 |
DDR1333 |
Also See:
Dual
Channel vs Triple Channel Memory | Flash Memory Cards
| When to
Upgrade Memory |
Tech Tools Knowledge Base
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