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Double word boundary?
Posted: Thu Jul 11, 2013 3:08 pm
by cobollearn
Hi,
What is Double-word-boundary in COBOL? What does it signify? Are there other such "boundaries"?
Re: Double word boundary?
Posted: Thu Jul 11, 2013 3:25 pm
by Robert Sample
From the first days of the 360 machine, back in 1964, memory has been divided into 4-byte chunks called words. Bytes 0 to 3 represent the first word, bytes 4 through 7 represent the second word, and so forth. A double-word boundary is byte 0, 8, 16, .... and certain Assembler instructions need data aligned on double-word boundaries. There are now quad-word boundaries (0, 16, 32, ...) with the advent of 64-bit addressing, but they're not much used (yet).
Re: Double word boundary?
Posted: Tue Apr 29, 2014 1:35 pm
by cobollearn
Thanks Robert.
What does it mean that "data aligned on double-word boundaries"?
Re: Double word boundary?
Posted: Tue Apr 29, 2014 3:07 pm
by nicc
It means that the data element starts on a double-word boundary which Robert has described above - basically an address that is evenly divisible by 8 or is 0 (hence the 0, 8, 16 etc in robert's post)
Re: Double word boundary?
Posted: Tue May 06, 2014 12:05 pm
by cobollearn
Ok. Thanks, hopefully I'll start understing these things more as I progress.