On Alpha systems, the $RAB64 macro allocates storage for a RAB64
    and initializes certain RAB64 fields with defaults and user-
    specified values. You cannot use this macro within a sequence of
    executable instructions. No value is returned for this assembly-
    time operation.

    The defaults unique to $RAB64 are as follows:

    o  RAB64$B_BLN is initialized to RAB64$C_BLN64.

    o  The original longword I/O buffers (KBF, RHB, RBF, and UBF) are
       initialized to -1; USZ and RSZ word sizes are initialized to
       0.

    User-specified values using the CTX, KBF, RHB, RBF, RSZ, UBF,
    or USZ keywords are moved into the quadword fields for these
    keywords. In contrast, the $RAB macro moves them into the
    longword (or word) fields for these keywords.

    Format

      $RAB64  BKT=bucket-code-number,

              CTX=user-context-value,

              FAB=fab-address,

              KBF=key-buffer-address,

              KRF=key-of-reference-number,

              KSZ=key-size,

              MBC=multiblock-count-number,

              MBF=multibuffer-count-number,

              PBF=prompt-buffer-address,

              PSZ=prompt-buffer-size,

              RAC={KEY|RFA|SEQ},

              RBF=record-buffer-address,

              RHB=record-header-buffer-address,

              ROP=<ASY BIO CCO CDK CVT EOF EQNXT ETO FDL KGE KGT LIM

              LOA LOC NLK NXR NXT PMT PTA RAH REA REV RLK RNE RNF RRL

              TMO TPT UIF ULK WAT WBH>,

              ROP_2=<NQL NODLCKWT NODLCKBLK>,

              RSZ=record-size,

              TMO=time-out-number-of-seconds,

              UBF=user-record-buffer-address,

              USZ=user-record-buffer-size,

              XAB=xab-address