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Offering
the complete solution for all memory module configurations with PLL
Clock Drivers, and Registered Logic Buffers (optional FET Bus Switches
are also available). Also see DDR
I & II for additional information. |
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Applications for the Memory Module
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Typical applications served are desktops, workstations,
servers, portables, and new communications products such as routers
and switches. DDR memory is clocked at the same speed as normal rates
(i.e. 100/133/166 MHz). The primary advantage of DDR is that it transfers
double the amount of data by utilizing both the rising and falling
edges of the clock signal. PC100/133 only transfers on the rising
edge. This allows the DDR module to transfer data twice as fast.
At a 133 MHz clock rate, DDR memory transfers data at 266 million
times per second, while PC133 transfers 133 million times per second. |
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| Terminology |
(a) Density/Capacity: 256MB,
512MB, 1GB or 2GB.
(b) Speed: PCxxxx denotes module transfer speed.
(c) Unbuffered or Registered: Unbuffered DIMM is normally
used for desktop and laptop computers. Registered DIMM
is used for higher performance systems such as servers,
workstations, routers and switches. To assure data integrity,
Registered DIMM uses additional devices: One to two registers
to latch address and command signals and one PLL clock
buffer to adjust timing.
(d) Planar or Stacked: To double the capacity of the
module, some vendors have stacked two memory chips on
top of one another. This type is called Stacked DIMM.
In contrast, the normal one is called Planar DIMM.
(e) Standard or 1-U DIMM: Standard height of the DIMM
is 1.7". Newer DIMMs are 1.2" or shorter; these
are referred as 1-U DIMM and typically used in the blade
server where height is limited. Naming Conventions Module
vendors use the PC-xxxx, which signifies the module data
rate in MB/s (Mega-Bytes per second). Memory vendors
adopted the DDR-xxx that signifies memory data rate for
each pin in MHz (Mega-Hertz). For example: 2GB Stacked
PC2700 Registered DIMM has the capacity of storing about
2 billion words (2GB) of data. PC2700 means:
(a) The transfer speed is 2.7 billions words per second.
It can transfer the whole content of its memory in less
than 1 second.
(b) It can be used in systems with any bus speed up to
200MHz. i.e. 100, 133, 166 or 200MHz. |
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