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From: robin on 8 Aug 2010 07:03 "Richard Maine" <nospam(a)see.signature> wrote in message news:1jmuykj.x0fe2h14oke2iN%nospam(a)see.signature... | robin <robin51(a)dodo.com.au> wrote: | | > "Richard Maine" <nospam(a)see.signature> wrote in message | news:1jmsnwd.1y8u6r31f3t1oeN%nospam(a)see.signature... | | > | That meant you could get a spurious end of record | > | by printing two colons in a row (the character code for a colon was | > | binary zero), though only if the colons happened to be in the last 12 | > | bits. | > | > And, of course, the two colons weren't printed. That happened because | > CDC tried to cram 65 different characters into a 6 bit field. | | I wouldn't have even seen Robin's comment if someone else hadn't replied | to it. I see that his accuracy is about at its usual level (which I'll | leave unspecified, so he can take that as a compliment if he wants :-)). | | No, it had nothing to do with some imaginary character set. The colon | was a perfectly fine part of the 64-character set that was used at our | site. We didn't use the 63-character set, and I'm not familliar with | anyone other than Robin's imagination having a 65-character one. The 64-character set was the result of having 6-bit characters. CDC attempted to have also one character to serve as end-of-record indication. CDC chose 12 bits of zeros as that character. As the colon was assigned to to the zero configuration, that meant that there were 65 characters. Clearly there was a conflict, and it revealed itself as a line being unexpectedly split over two print lines, with the pair of colons being suppressed.
From: robin on 8 Aug 2010 07:28 "Richard Maine" <nospam(a)see.signature> wrote in message news:1jmvifu.qjyy60pyz6c4N%nospam(a)see.signature... | robin <robin51(a)dodo.com.au> wrote: | | > | > CDC tried to cram 65 different characters into a 6 bit field. | ... | | > which amounts to 65 functions associated with 6 bit characters, | > whch is what I say they tried to do | | No, you said 65 characters, as quoted above. Same thing. CDC had 64 printable characters, with one character serving the purpose of a record terminator (which was a data byte). Total: 65. | characters /= functions | Record termination does not necessarily involve either characters or | functions. It did in this case.
From: robin on 8 Aug 2010 07:47 "Dr Ivan D. Reid" <Ivan.Reid(a)ivan.fsnet.co.uk> wrote in message news:slrni5nem7.1uk.Ivan.Reid(a)smtp.orangehome.co.uk... | My experience with a Cyber in 1978 was that it had a 60-bit word | but integer multiply/divide only worked up to 48 bits. To shift a 48-bit | integer to 60 bits to add a 5th 12-bit byte I had to use successive adds | (i=i+i). There was a shift instruction that would have done the job in one step. | That was just one of the Procrustean methods I had to use to | force it to output 8-bit punched tape object files from a National SC/MP | cross-assembler.
From: mecej4 on 8 Aug 2010 08:35 robin wrote: > "Richard Maine" <nospam(a)see.signature> wrote in message > news:1jmvifu.qjyy60pyz6c4N%nospam(a)see.signature... > | robin <robin51(a)dodo.com.au> wrote: > | > | > | > CDC tried to cram 65 different characters into a 6 bit field. > | ... > | > | > which amounts to 65 functions associated with 6 bit characters, > | > whch is what I say they tried to do > | > | No, you said 65 characters, as quoted above. > > Same thing. > CDC had 64 printable characters, with one character > serving the purpose of a record terminator (which was a data byte). > Total: 65. > > | characters /= functions > | Record termination does not necessarily involve either characters or > | functions. > > It did in this case. It seems to me that the last few posts in this thread (about 64 or 65 characters on the CDC) indicate that the colon may have been used as an escape character, somewhat like the backslash, \ , in C, with a pair of backslashes being then needed to signify the literal character. This is speculation on my part, but this may throw some light on why two colons had quite a different effect than the once-repeated effect of a single colon. -- mecej4
From: Nick Maclaren on 8 Aug 2010 08:55
In article <i3m8ad$99i$1(a)news.eternal-september.org>, mecej4 <mecej4.nyetspam(a)opFeramail.com> wrote: > >This is speculation on my part, but this may throw some light on why two >colons had quite a different effect than the once-repeated effect of a >single colon. I would trust what Richard Maine says, and ignore anything that conflicts with it. Certainly in this context. Regards, Nick Maclaren. |