I thought the -27 had 32760 cyls and the -54 had 65520 cyls. Why they
chose these values I do not know.
32760 = X'7FF8' which is the largest signed half-word value (minus 7
cylinders for reasons I forget). This could be implemented without
affecting most IBM, ISV, and user code which did signed half-word
arithmetic on the cylinder number.
65520 = X'FFF0' which is the largest unsigned half-word (minus 15
cyilnders). This implementatin required that all code which calculates
cylinder numbers change to unsigned arithmetic, which was a lot more
extensive.
In the currently define disk CCW architecture, the cylinder number is an
unsigned halfword, so IBM can't increase the disk size any more without
introducing a new architecture and changing a lot of control blocks
which contain cylinder numbers. This will require even more extensive
changes on everyone's part, but we understand that IBM is still thinking
about doing something along this line.
--
Bruce A. Black
Senior Software Developer for FDR
Innovation Data Processing 973-890-7300
personal: [EMAIL PROTECTED]
sales info: [EMAIL PROTECTED]
tech support: [EMAIL PROTECTED]
web: www.innovationdp.fdr.com
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO
Search the archives at http://bama.ua.edu/archives/ibm-main.html
