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DDR2 SDRAM has several improvements over DDR SDRAM. DDR2 SDRAM clock rates are higher, thus increasing the memory data rates (See Table 2). Signal integrity becomes more important for reliable memory operation as the clock rates increase. As clock rates increase, signal traces on the circuit boards become transmission lines and proper layout and termination at the end of the signal traces becomes more important.
DDR2 SDRAM reduces memory system power by operating at 1.8 volts, which is 72% of DDR SDRAM’s 2.5 volts. In some implementations, the number of columns in a row has been reduced, resulting in lower power when a row is activated for read or writes.
A new feature introduced with DDR2 SDRAM is additive latency, which provides the memory controller hub the flexibility to send the Read and Write commands sooner after the Activate command. This optimizes memory throughput and is configured by programming the additional latency using the DDR2 SDRAM extended mode register.
DDR2 SDRAM improves data bandwidth of 1Gb and 2Gb DDR2 SDRAMs by using eight banks. The eight banks increase the flexibility of accessing large memory DDR2 SDRAMs by interleaving different memory bank operations. Also, for large memories, DDR2 SDRAM supports a burst length up to eight.
DDR2 SDRAM data sheets are over 100 pages and the above DDR2 SDRAM features are highlights of its key features. Refer to DDR2 SDRAM data sheets for their complete features and details of operation.
DDR2 SLOTS
DDR2 SDRAM Data Rate Memory Clock
DDR2-400 400 Mb/s/pin 200 MHz
DDR2-533 533 Mb/s/pin 266 MHz
DDR2-667 667 Mb/s/pin 333 MHz
DDR2-800 800 Mb/s/pin 400 MHz
DDR2-1066 1066 Mb/s/pin 533 MHz
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