FB-DIMM : Benefits (Simplified board design, Higher memory.)

TIM

MemoryToday.com :: ผู้ให้บริการเพิ่มแรม อันดับ 1 ของประเทศไทย!! จัดส่งและติดตั้งถึง Office และ EMS โทร. 02-874-4531

Benefits

The benefits of FB-DIMM architecture include
• Simplified board design
• Higher memory capacity
• Higher performance
• Improved reliability

Simplified board design
FB-DIMMs use a 240-pin socket similar to that used for traditional DDR2 registered DIMMs; however, FB-DIMMs require significantly fewer signal traces. FB-DIMMs have 69 signal traces compared to 138 traces for DDR2 registered DIMMs. These traces have to be routed to every DDR2 DIMM on the channel, which complicates board design. FB-DIMMs have additional traces for the secondary links between sockets, but these traces do not add to overall routing complexity.

In addition, the memory controller and AMB can compensate for signal traces of unequal length, thus eliminating the need for odd routing paths to make sure the timing is correct. The lower number of signal traces and the ability to use traces of unequal length greatly simplify board design for FB-DIMMs.

Higher memory capacity
The point-to-point FB-DIMM architecture enables the electrical load (and signal integrity) for each channel to remain constant, even as FB-DIMMs are added. This allows system designers to have up to 8 DIMMs per channel (no rank limits) while maintaining a low soft error rate (Figure 5). In comparison, PC2-3200 SDRAM can have a maximum of 2 dual-rank DIMMs (or 4 single-rank DIMMs) per channel

Higher performance
The asynchronous serial links between the memory controller and AMB enable higher performance by the memory subsystem. The two devices operate on independent clocks, so the transmitting device embeds a bit clock with the data stream. The bit clock consists of a start bit that indicates the beginning of a chunk of information, or data word, and a stop bit that indicates the end of the data word. This eliminates skew between the clock and the data—an issue with parallel interfaces—and allows very high data rates to be achieved.

As described previously, the outbound links exhibit one-half the peak theoretical throughput of the inbound links. For FB-DIMMS with DDR2-533 DRAM devices, the outbound links have a theoretical throughput of 2.1 GB/sec, or approximately one-half of 4.3-GB/s inbound links (Figure 6). Because the serial links transport write and read data simultaneously, the total theoretical throughput of the FB-DIMM channel is 6.4 GB/s (2.1 GB/s plus 4.3 GB/s). When using DDR2-667 DRAM, the total theoretical throughput of the FB-DIMM channel is 8.0 GB/s (2.7 GB/s plus 5.3 GB/s)

Improved reliability
FB-DIMM technology improves reliability through extended use of ECC and the introduction of a new fail-over mechanism. FB-DIMMs extend the use of ECC to protect commands and address information in the event of a soft error. This feature can help reduce instances where the soft error could disrupt server performance and reliability. A second data protection mechanism called “bit lane fail-over” correction identifies a bad data path and removes it from service.

Information provided by Hewlett-Packard Development Company, L.P.