Subject: Re: MIT ChaosNet code port to Linux From: Erik Naggum <erik@naggum.net> Date: Fri, 21 Jun 2002 03:26:32 GMT Newsgroups: comp.lang.lisp Message-ID: <3233618791984888@naggum.net> * Barry Margolin | Once ASCII became the standard character set, you were pretty much forced | to use at least 7 bits. As far as I can see from the historical record, DEC always used 7-bit ASCII on their PDP-10 series operating systems. I have no record of PDP-6 systems. | 6-bit ASCII is only usable if you're willing to forego lowercase. Actually, there is no such thing as 6-bit ASCII. SIXBIT has no control codes and is completely useless except in extremely well-controlled settings. There is no support for printing or typing SIXBIT files, for instance -- if files were opened with 6-bit bytes, they would appear to contain 32 control codes and the first 32 non-letter ASCII character -- hardly useful. (Yes, I have tried this, back in the summer of 1980, wasting huge amounts of paper due to the unfortunate placement of certain control codes.) | I think it was used in directory files (the filename and filetype were each a | single word, allowing each component to be up to 6 monocase characters), but | file contents were generally 7-bit ASCII. At least under TOPS-10, the right half of the file type word was used for the CFP (compressed file pointer) into the RIB (retrieval information block) in the UFD (user-file directory) or SFD (sub-file directory), so you could have only three letters in the file type, but six in the file name, thus a directory entry was formed by two machine words. (For completeness, the UFD was itself a file with extension .UFD in the MFD (master file directory.)) [All according to my trusty old TOPS-10 Monitor Calls Manual, Volume 1, from February 1984.] | BTW, I think ASCIZ means "ASCII with Zero-byte terminator", a la C strings. Correct. | Multics, another 36-bit system, also used 9-bit characters. But since | ASCII was only 7 bits, this wasted much more than ITS's 7-bit characters: 2 | bits/character versus 7 bits/5 characters, or 25% more words used to hold | the same number of characters. In the days when memory (both physical and | virtual) was extremely expensive, this could make a big difference. I did not follow that computation, but the number of words to hold a file of 9-bit characters (four to a word) compared to 7-bit characters (five to a word) would indeed be (/ 1/4 1/5) => 5/4 or 25% more. -- Guide to non-spammers: If you want to send me a business proposal, please be specific and do not put "business proposal" in the Subject header. If it is urgent, do not use the word "urgent". If you need an immediate answer, give me a reason, do not shout "for your immediate attention". Thank you.