VMS Help Sys Parameters, CRD_CONTROL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This special parameter is used by Compaq and is subject to
    change. Do not change this parameter unless Compaq recommends
    that you do so.

    On VAX systems, CRD_CONTROL serves the function of CRDENABLE in
    earlier releases. On Alpha systems, CRD_CONTROL can be used to
    expand the function defined by CRDENABLE.

    CRD_CONTROL is a bit mask for corrected read data (CRD) soft
    error control flags. These flags control the use of CRDERROR
    routines.

    On VAX systems, the following bits are defined:

    Bit   Description

    0     Enables CRD processing for all systems.

    1     Enables scrubbing (rewriting) of the memory location that
          induced the CRD.

    2     Enables page replacement of the pages that exhibit repeated
          CRD errors.

    3     Forces all memory pages to be included in the PFN database.
          On systems that contain more than 512 megabytes of memory,
          all memory is mapped by the PFN database by default. This
          bit allows the mapping to occur on systems with less than
          512 megabytes of memory.

    Default values are different for VAX and Alpha systems. On
    VAX systems, the default is 7, which enables CRD processing,
    scrubbing, and page replacement.

    On Alpha systems, the following bits are defined:

    Bit    Description

    0      Enables CRD processing for all systems.

    1      Enables scrubbing (rewriting) of the memory location that
           induced the CRD.

    2      Enables page replacement of the pages that exhibit
           repeated CRD errors.

    3      Forces all memory pages to be included in the PFN
           database. On systems that contain more than 512 megabytes
           of memory, all memory is mapped by the PFN database by
           default. This bit allows the mapping to occur on systems
           with less than 512 megabytes of memory.

    4      Enables extended CRD handling, if available.

    5      Enables loading of driver and process for handling server
           management events. Platform-specific code usually sets
           this bit if the required hardware and firmware support are
           available.

    24-31  Reserved for platform-specific error-handling control.

    On Alpha systems, the default setting is 22, which enables
    CRD processing, scrubbing, page replacement, and extended CRD
    handling.