Memory compression could reduce server costs

IBM and Broadcom have struck a deal to develop memory compression technology that Big Blue claims can double memory density, reducing costs and improving performance.

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By  Jon Tullett Published  January 31, 2001

IBM has inked a deal with Broadcom that promises to reduce the cost of server systems by using memory compression technology.

The Memory Extension Technology (MXT) is still under development, but will allow systems to compress data on the fly, using the same algorithms as the popular PKzip software. The technology can be configured to either increase the capacity of the memory by compressing stored data, or to nearly double the throughput of the server by compressing data in transit. The net result will be either similar performance at lower cost, or greater performance with no increase in cost, IBM said.

IBM is preparing MXT for use in its rack-optimised xSeries line of servers. MXT will be integrated inside ServerWorks' "Pinnacle" chipset, and could be later applied to IBM's hard drives as well.

From internal tests, IBM claims that data can be compressed anywhere from 14 percent to 50 percent of its original size. If the data has already been compressed - a ZIP file, for instance - the MXT technology senses this and ignores the data, since compressing an already-compressed file typically increases its file size, as extra bits are added by the compression algorithm.

Using the MXT technology results in "no measurable performance loss" inside the server, said Chuck Schulz, a researcher at IBM's T.J. Watson Research Center. The MXT technology reads data at an effective rate of 2 Gbit/s from main memory, and feeds it into an undisclosed amount of DDR DRAM, which serves as a level-3 cache.

IBM currently includes a PCI device driver to fool the operating system into believing the compressed memory is actual physical DRAM, and IBM is working with Microsoft and Linux vendors into incorporating MXT support directly into the OS, Schulz said.

According to Tom Bradicich, director of computer architecture and technology for IBM's xSeries servers, how the MXT technology will be deployed is still being assessed. IBM's plan, which has not been completely finalized, is to allow customers to reduce the amount of memory within the company's xSeries line of rack-optimised 1U servers. IBM is tentatively planning to roll the technology out in the second half of this year, Schulz said.

Since the MXT technology is implemented in the Pinnacle chipset, the compression can be applied to any off-the-shelf memory, IBM said. IBM has historically taken new technologies, such as its "chip-kill" method of rerouting data around a faulty DRAM chip, and moved them into its chipsets.

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