Re:Re: Maximum Page Size for IDMS Database Files

  • 1.  Re:Re: Maximum Page Size for IDMS Database Files

    Posted 07-18-2006 06:11 AM
    Dusting off the cobwebs from my brain I seem to remember that the 32K
    restriction was in the I/O subsystem. When an access method, like BDAM or
    QSAM, built EXCP commands the op codes, address, flag bytes and byte count
    were placed into a channel command word (CCW) which was actually two words
    long. In the original (format-0) version the data address was limited to 24
    bytes so all I/O was placed below he line. Later in the format-1 version of
    the CCW the address field was opened up to 31 bits so I/O could go directly
    above the line. However, in both formats the byte count field would only
    support 32k.

    I believe (but not positive) that there is now a format-2 CCW which can
    obtain a larger byte count. So if the hardware device supports larger
    blocks, the access method has been updated to use the format-2 CCWs, and the
    IDMS internal software and control blocks can support the larger pages; then
    you should be good to go. But that is a few ifs.

    Bill Boyce
    GE Money