On the REALLY old boxes (S/360), the performance problem was called a S0C6 specification exception program interrupt and probable ABEND. When the first S/370s were shipped in 1971, the requirement for storage alignment was removed for most instructions, but there was a performance hit.
Bill Fairchild Software Developer Rocket Software 275 Grove Street * Newton, MA 02466-2272 * USA Tel: +1.617.614.4503 * Mobile: +1.508.341.1715 Email: bi...@mainstar.com Web: www.rocketsoftware.com -----Original Message----- From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of Edward J Mulleady Sent: Wednesday, December 09, 2009 7:25 PM To: IBM-MAIN@bama.ua.edu Subject: Re: curiousity q? for the historians. "In reality, only the first byte of the BB is actually used. Why waste a byte?" John... Maybe IBM wasted a byte to keep the rest of the record at least halfword aligned, assuming that the record was read into a halfword aligned address (fullword usually was the case). On the old boxes, there was a performance penalty using halfword instructions (LH, STH, AH, SH) on a field that was not halfword aligned. In the old days, I would always design my records so that the halfword and fullword fields fell on the proper boundary. Or maybe the extra byte was "reserved for future use". Ed... ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
