Memory Terminology:
Generic Memory:
Our Generic memory conforms fully to industry standard configurations. However,
there are many variations among machines, so while we guarantee that our Generic
memory conforms to specification, we cannot be absolutely positive that your
particular computer model 100% conforms to the same specification. Our Generic
listings for different models of computer are based on our best research and
experience, but are not to be considered a guarantee of compatibility.
Kingston Guaranteed Compatibility:
If you are looking for a module and guaranteed to work with your specific model
of machine, our Kingston Brand memory is tested and certified for each particular
model, and is guaranted to match that model's requirements.
ECC - Error Correcting RAM - also called Parity
ECC RAM has an extra error-correcting bit (9 bits instead of 8) for higher reliability
in servers and high-end machines. Most forms of RAM (SIMMs, DIMMs, RDRAM and
DDR RAM) are available in either ECC or Non-ECC. Most common computers use Non-ECC
(standard) memory. In order to use ECC RAM,
If you have a machine that can take either ECC or Non-ECC and are unsure what to order, either check the RAM that is already installed, or check your purchase invoice for the machine, which should indicate whether ECC was installed or not initially.
Reading memory chip part numbers: You can sometimes read from the part number whether the RAM in your machine is ECC (Parity). ECC RAM often has a number in the pat number that is a multiple of 9, where Non-ECC would have a multiple of 8. Example, RAM that has x18 or x36 or x72 in the number would be ECC, compared to Non-ECC with x16 or x32 or x64.
Non-ECC RAM also called Non-Parity RAM
Unless specified otherwise, all standard RAM is Non-ECC.
SIMM - Single Inline Memory Module
Found in older desktops and many laser printers, in 72-pin packages, and less
commonly 30-pin. Sometimes must be installed in pairs. Whether a SIMM is FPM
or EDO memory (see below) is significant.
DIMM - Dual Inline Memory Module
Found in desktop machines and servers, PC66, PC100 and PC133 are all different
speeds of DIMMs in a 168 pin package, there are also SDRAM DIMMs that predate
the PC66 standard. DDR memory is also technically a DIMM format, but is seldom
referred to as such.
SO-DIMM - Small Outline Dual Inline Memory Module
Most often found in laptops. Most SO-DIMMs are 144 pin packages - there are
also DDR 200 pin SO-DIMMs and some rare 72 pin SO-DIMMs
Micro-DIMM
Rare, smaller than the SODIMM format, found in a few Sony laptops
RIMM, RAMBus, also called RDRAM
RAMBus memory module. Most often, RAMBus memory must be installed in pairs.
32-bit RAMBus moduled have been introduced which only need to be installed singly
- the motherboard has to specifically support 32-bit RAMBuss to use these.
Speeds are PC800 and PC1066. The PC600 and PC700 designations are obsolete and
PC800 can be substituted.
DDR - Dual Data Rate RAM
Can be packaged in both DIMM (184-pin for Desktops) and SO-DIMM (200-pin for
laptops) forms. Speeds are PC2100 (266 MHz), PC2700 (333 MHz). The standards
for 400 MHz DDR are not completely finalized, although some manufacturers are
offering high speed DDR modules.
FPM - Fast Page Mode
EDO - Extended Data Out
These two terms refer to older (c. 1998 and earlier) RAM produced before the
introduction of the PC66 standard. SIMMs, DIMMs and SO-DIMMs can be either EDO
of FPM, in many cases they cannot be substituted for each other. EDO modules
are rising in price rapidly because the components are no longer being manufactured
by most chipmakers. It is not unusual for an EDO SO-DIMM for an older laptop
to cost hundreds of dollars. The distinction between EDO and FPM is irrelevant
with PC66, PC100, PC133, RAMBus and DDR RAM types.
Density:
When a RAM module is built, the manufacturer can design it using high density
or low density chips. For example, modules built with 4 x 32Mb chips, 8 x 16Mb
chips or 16 x 8Mb chips all come out to the same amount of RAM. However, the
memory controller circuit in a computer must be able to address the chips on
the module - if the memory controller cannot address higher density chips, that
computer will only function with modules built with lower density chips.
Profile:
The physical size of the RAM module, both in height and in thickness. Some machines,
particularly laptops, have physical space limitations that demand low-profile
modules.
PC66, PC100, PC133:
These are standards for DIMMs and SO-DIMMs that specify memory bus speeds of
66 MHz, 100 MHz and 133 MHz. In broad terms, you can substitute faster RAM into
a machine (putting PC133 into a machine that specifies PC100, for example),
however there are still a significant number of earlier PC66 and PC100 machines
that are incompatible with modern PC133 modules for reasons of chip density
and differences in the supporting chips on the module (buffer, EPROM, Serial
Presence Detect).
Clock:
To oversimplify a complex discussion, the timing of a RAM module is often described
by a Clock value. Typical values are CL3, CL2 and CL2.5. A CL2 (2-clock) module
is not necessarily faster than a CL3 module - the effective speed is determined
by the memory controller on the motherboard of the computer, and in some cases
a CL3 module matches the motherboard timing better.
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