From owner-freebsd-chat@FreeBSD.ORG Sat Dec 20 16:33:33 2003 Return-Path: Delivered-To: freebsd-chat@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D215F16A4CE for ; Sat, 20 Dec 2003 16:33:33 -0800 (PST) Received: from cruzio.com (dsl3-63-249-85-132.cruzio.com [63.249.85.132]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8F72043D55 for ; Sat, 20 Dec 2003 16:33:30 -0800 (PST) (envelope-from brucem@mail.cruzio.com) Received: from mail.cruzio.com (localhost [127.0.0.1]) by cruzio.com (8.12.10/8.12.10) with ESMTP id hBL2VvKV000246 for ; Sat, 20 Dec 2003 18:31:57 -0800 (PST) (envelope-from brucem@mail.cruzio.com) Received: (from brucem@localhost) by mail.cruzio.com (8.12.10/8.12.10/Submit) id hBL2Vv6d000245 for chat@freebsd.org; Sat, 20 Dec 2003 18:31:57 -0800 (PST) (envelope-from brucem) Date: Sat, 20 Dec 2003 18:31:57 -0800 (PST) From: "Bruce R. Montague" Message-Id: <200312210231.hBL2Vv6d000245@mail.cruzio.com> To: chat@freebsd.org Subject: Re: A bit of trivia: what does usr stand for? X-BeenThere: freebsd-chat@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Non technical items related to the community List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 21 Dec 2003 00:33:33 -0000 I don't know anything about the derivation of the name "usr", but it is of mild interest that one reason 3-letter filename suffixes are so common (.exe, .jpg, .com, .txt, etc..) is that many old DEC machines (including the PDP-11) used a character set called "rad 50" (or RADIX-50, Radix 50, etc..). Rad 50 had 40 characters (50 in octal), and could store 3 characters in 16 bits. A number of filesystems used a single 16-bit word for the filename suffix in dir structures and such, and thus the 3 char maximum on suffix lengths. If you ever had to work with rad-50 at low-level, you are liable to remember it, because characters were not aligned on bit boundaries but had to be inserted and extracted using a process similar to that used for converting between base 10 numbers in ASCII text and binary numbers. DRI used 3-letter suffixes for CP/M, likely because the RT-11 system at the NPS that seems to have strongly flavored CP/M used RAD-50. MS DOS, of course, inherited the convention from CP/M. None of this still has anything to do with Unix's "usr", but 3 letter name limitations were common at one time. RSX-11, another PDP-11 OS, had a one word rad-50 3 character maximum on command names; this (or other similar systems) may have influenced the use of common 3-character names such as "ddb"... or maybe not. There were a lot of similar character sets - Univac Fielddata, CDC Display Code.... These were all different of course. Dealing with char conversion in mainframe days was a mess. Of course, today these days 3 char suffixes (.htm) are probably just common because the statistics work out nice. - bruce