DDR stands here for Double Data Rate. It is a technology that transmits data on both sides of a tact signal.
This way the performance has been doubled; a 133 MHz SDRAM chip can very easy become altered to a 266 MHz DDR chip:
It should be pretty easy for the market to change for DDR RAM. The modules look like and operate quite similar to existing SDRAMs. We just need new chipsets to start the migration.
However, the modules hold 16 pins more than SDRAM do, so they do not fit into the same sockets.
Other terms used are:
VIA expects DDR to be used in all segments of the pc market. Intel, who is behind the Rambus technology, only expects to use DDR in large servers, where you find several Gigabytes of RAM installed, and where RAM price really matters.
Intel is dedicated to the Rambus technology. In the summer 2000 it was revealed that Intel has comitted itself to the RAMBUS technology so they cannot implement DDR! This goes for all future desktop PCs until 2003, according to their agreement with Rambus Inc. Only the 64 bit server Itanium processor and it succesors Foster and McKinley are using DDR RAM.
We hope that Intel will change their strategy. We expect DDR-SDRAM to be cheaper than Rambus RAM for quite some time; yet it should give the same performance. Rambus represents a sophisticated technology, but with prices 5 times higher it is not a low-end product. Intel produces great chipsets for desktop PCs like i815E, and it would be sad if they abandoned this market. We want Intel and PC2100!
Reports in the summer 2000 told that Intel has licensed VIA to develop DDR-enabled chip sets for Pentium 4.
Hence it seems quite natural and in tune with the previous changes in RAM technology that we use the DDR standard for a couple of years. Before Rambus (or something even better) enters the market.
Below you see the theoretical bandwidts of different RAM types. However, SDRAM does not perform as good as the figures show. This is due to latencies; the CPU and other units cannot read the data at these speeds; they have to wait some clock circles in between each reading before the data transfers start. The same goes for DDR RAM.
|RAM type||Theoretical max. bandwidth|
|SDRAM 100 MHz||100 MHz X 64 bit= 800 MB/sec|
|SDRAM 133 MHz||133 MHz X 64 bit= 1064 MB/sec|
|DDRAM 200 MHz (PC1600)||2 X 100 MHz X 64 bit= 1600 MB/sec|
|DDRAM 266 MHz (PC2100)||2 X 133 MHz X 64 bit= 2128 MB/sec|
|DDRAM 366 MHz (PC2600)||2 X 166 MHz X 64 bit= 2656 MB/sec|
|RDRAM 600 MHz||600 MHz X 16 bit= 1200 MB/sec|
|RDRAM 700 MHz||700 MHz X 16 bit= 1400 MB/sec|
|RDRAM 800 MHz||800 MHz X 16 bit= 1600 MB/sec|
Read module 5a about expansion cards, where we evaluate the I/O buses from the port side.
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