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MXT Support Patch for Linux


Memory eXpansion Technology (MXT) is a hardware technology for compressing main memory contents. MXT effectively doubles the amount of memory. For example, 512 MB of installed memory appears as 1 GB. MXT is transparent to CPU, I/O devices, application software and device drivers: no software changes are needed.

The first commercial grade memory controller chip incorporating MXT, called Pinnacle, will be available from IBM's licensee ServerWorks Inc. Several computer vendors are working to incorporate this chip in to their motherboard designs, as well as designing new memory controllers incorporating main memory compression.

A corner case exists when 2 to 1 compressibility assumption breaks down, for example when memory contains already compressed data. The MXT support patch must be applied to the Linux kernel to deal with this condition. The document /usr/src/linux/Documentation/mxt.txt describes MXT and the support patch in detail. The 2.4 support was implemented as a device driver module and a less than hundred lines of a kernel patch.

(Please note that MXT is a hardware feature. An erroneous news article has been published in a trade magazine which suggested that software downloaded from this website will double the memory size of your plain old computer. This is not possible.)

Why do I need MXT?

Simply put, MXT buys you price/performance. You can either cut your memory costs by half. Or you can increase performance since with MXT the effective memory size is typically twice the installed memory size.

Watch the demonstration video (2.1 MB file)

How to buy MXT based servers?

Please visit IBM xSeries 330MXT web pages for more information.

How to get the MXT support software?

  • RedHat 7.2 supports MXT (10/2001)
  • RedHat 7.1 kernel upgrades support MXT hardware (10/2001)
  • Linux 2.4: Patches are available. Please check the MXT home page for the patches.

Publications and Documents

  • IBM Journal of Research and Development special issue Vol. 45, No. 2, 2001
  • MXT BIOS Specification: BIOS EBDA area will contain an MXT signature and table identifying hardware characteristics. Format of this table is detailed in this document.