Source : Free On-Line Dictionary of Computing

Memory Type Range Registers
     
         (MTRR) Registers in the {Pentium Pro}
        and {Pentium II} processors that can be used to specify a
        strategy for communication with the external memory and
        {caches} for a number of {physical address} ranges.
     
        Strategies include {write-through}, {write-back}, or
        uncached(?).  Such control is useful where the memory is
        located on a device and is accessed via some kind of device
        bus, e.g. a {PCI} or {AGP} {graphics card}, where caching
        would be of no benefit.
     
        (1999-07-02)