Two words: punched cards. Numbers on punched cards were "big-endian." IBM was the dominant power in tabulating machines and never wanted to let that advantage slip away.
Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf Of John McKown Sent: Wednesday, March 8, 2017 12:32 PM To: IBM-MAIN@LISTSERV.UA.EDU Subject: Re: curious: why S/360 & decendants are "big endian". On Wed, Mar 8, 2017 at 1:39 PM, Tom Marchant < 0000000a2a8c2020-dmarc-requ...@listserv.ua.edu> wrote: > On Wed, 8 Mar 2017 11:33:31 -0700, Paul Gilmartin wrote: > > >It probably save hardware to decrement as well as increment in > >accessing storage. Consider that CLC goes left-to-right but AP goes > >right-to-left. > > AP goes right to left because it would otherwise have to do more work > to propagate carry. > ​Right. But it could go to the left if the nybbles in the packed decimal number were in reverse order, with the sign nybble being the first (leftmost) nybble in the data stream. I.e. instead of 01234F be F43210 . But that was likely not acceptable because one reason that programmers love packed rather than binary is that they can read it directly in the hex dump. Said dump being far more prevalent tool for debugging in the far past. Some decisions are not really hardware dictated. They're cultural. > CLC goes left to right because it can stop as soon as it finds a > mismatch and recognize which is greater. If all you wanted to check > for was that the two are equal, you could go either way, but that's not as > useful. > > -- > Tom Marchant > > -- "Irrigation of the land with seawater desalinated by fusion power is ancient. It's called 'rain'." -- Michael McClary, in alt.fusion Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
