HP 117755-003 740 Vue d'ensemble - Page 19

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With the high data rate of Rambus, signal integrity is troublesome. System boards must be designed

to accommodate the extremely stringent timing of Rambus, and this increases product time to market.

Additionally, each Rambus channel is limited to 32 devices, imposing an upper limit on memory

capacity supported by a single bus. Use of repeater chips enables use of additional devices and

increases potential memory capacity, but repeater chips have been very challenging to design.

Finally, the larger dies and more limited production of RDRAM compared to those of other memory

technologies have increased the cost of RDRAM. RDRAM still costs up to twice as much as SDRAM.

RDRAM technology offers performance advantages and lower pin count than SDRAM and DDR

SDRAM. However, SDRAM and DDR SDRAM offer more memory capacity and lower cost than

RDRAM.

Importance of using HP-certified memory modules in

ProLiant servers

Customers should use only HP memory option kits when replacing or adding memory in ProLiant

servers. This section describes two of the most important reasons.

First, not all DIMMs are created equal; they can vary greatly in quality and reliability. In the highly

competitive memory market, some third-party memory resellers forego the level of qualification and

testing needed for servers because it adds to the price of DIMMs. HP uses proprietary diagnostic tools

and specialized server memory diagnostic tests that exceed industry-standards to ensure the highest

level of performance and availability for ProLiant servers. The costs of system downtime, data loss,

and reduced productivity caused by lower quality memory are far greater than the price difference

between HP-certified memory and third-party DIMMs.

Second, use of HP memory option kits prevents improper mixing of single-rank and dual-rank DIMMs.

Although single-rank and dual-rank DIMMs may have the same capacity, they differ in the way in

which they are accessed by the chipset (see the "DIMM configurations" section). Therefore, to ensure

that the server boots properly and operates reliably, single-rank and dual-rank DIMMs should not be

used in the same bank. On the other hand, some ProLiant server platforms have configuration

guidelines that allow the mixing of single-rank and dual-rank DIMMs. HP memory option kits precisely

match the capabilities and requirements of the ProLiant server for which they are designated.

Therefore, they prevent improper mixing of single-rank and dual-rank DIMMs.

HP memory option kits are listed in each server's user guide and in the product QuickSpecs available

at www.hp.com.

Conclusion

The increasing performance gap between processors and memory has generated development of

several memory technologies. While some memory manufacturers prefer a revolutionary approach to

memory technology development, others favor an open, evolutionary approach. Memory

manufacturers must balance the cost of performance enhancements against the laws of physics and

compatibility with existing technologies. HP will continue to evaluate relevant memory technologies in

order to offer customers products with the most reliable, best performing memory at the lowest

possible cost.