Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83 SMI; site sun.uucp Path: utzoo!watmath!clyde!burl!hou3c!hocda!houxm!vax135!cornell!uw-beaver!tektronix!hplabs!hpda!fortune!amd!decwrl!sun!gnu From: gnu@sun.uucp (John Gilmore) Newsgroups: net.arch Subject: Re: Global memory usage in the 1401 Message-ID: <1689@sun.uucp> Date: Mon, 24-Sep-84 02:23:06 EDT Article-I.D.: sun.1689 Posted: Mon Sep 24 02:23:06 1984 Date-Received: Tue, 25-Sep-84 06:48:28 EDT References: loral.444 Organization: Sun Microsystems, Inc. Lines: 17 Bill Price says: > Actually, the designers of the 1401 did something even worse than hiding it: > they used this global thing for a very local purpose. The cell addressed by > the address zero was used as the row counter for the card reader! This was not especially bad, considering that locations 1-80 of memory were permanently reserved for the card reader. The "read card" instruction (opcode "1") would fill locs 1-80 with the contents of the next card in the reader. 101-180 was the area that would get punched if you did a "2" opcode. 201-332 got printed if you did a "4" opcode. Guess what happened if you executed a "7"? [It did all three at once. This was the only way to overlap I/O until much later in the 1401's design cycle.]