This directory contains a modified version of Brian Nelson's VMSTPC tape copy
program.  This version (VMSXTPC) has two features not found in the original:
first, it supports tape blocks of up to 64KB; second, it supports data
compression in the container file.

Large tape block support is accomplished by writing large blocks as multiple
container file records.

Data compression, which is selected by default but may be turned off with the
/NOCOMPRESS qualifier, is done using my QLZW "quick LZW" record-at-a-time
compression routine.  Warning -- this routine uses a lot of memory!  If you
select compression, specify 30 buffers, and try to process a tape with 64KB
blocks, your WSEXTENT should be at least 20480.  Decompression requires far
less memory.  However, with a compressed container file, you can reduce the
disk space required to store a tape by 50% or more.  Given enough memory to
eliminate page faults, TPC appears to be able to compress on the fly and keep
up with a 4mm DDS-DC tape drive when running on VAX CPU's of 6 or 7 VUPs.  Your
mileage may vary.

Please send any questions or comments about the TPC modifications or the QLZW
routine to John Osudar (osudar@cmt.anl.gov).