On Thu, 2024-12-12 at 16:53 +0800, jeremy ardley wrote: > > > On 12/12/24 16:18, Bret Busby wrote: > > > > > > The first computer I was paid to write software for, in 1966, had > > > 1,400 6-bit characters, not bytes, > > > > Wasn't that data type named EBCDIC, or something like that? > > That would be 6 bit BCD - a precursor to EBCDIC which was an IBM 8 > bit > encoding most commonly implemented using 80 column punch cards
BCD meant "Binary Coded Decimal." EBCDIC meant "Extended Binary Coded Decimal Interchange Code." The correspondence between card code and BCD was straight forward. The six-bit code was divided into two parts, a four-bit part called "digit" and a two-bit part called "zone." The bits were called 8421 and zones were called BA. The bottom ten rows on an IBM card were numbered 0-9, and represented digits. Rows with digit- only punches mapped directly to the "digit" part of a character, except that zero in binary represented blank and "zero" was represented by 8- 2 (ten). The top two rows were called "12" and "11" and represented zones, but their encoding was not quite as straight forward. The 12 row set both A and B zones, the eleven row set the B zone, and if there was a punch in addition to the zero row, it set the A zone. Other codes were fairly straight forward. A-I were represented by a 12 (AB) zone plus 1-9, J-R were represented by an eleven (B) zone plus 1-9, slash was represented by a zero (A) zone plus 1, and S-Z were represented as 0 plus 2-9. Figures such as equal sign had binary "digit" part representations greater than ten, so, for example, equal sign was 11 (8-2-1), represented by 3-8 on a card, and comma was A-8-2-1, represented by 0-3-8 on a card. See page 170 in http://bitsavers.org/pdf/ibm/1401/A24-1403-5_1401_Reference_Apr62.pdf > An alternative format for 80 column punch card format was Burroughs > BCDIC Univac had a six-bit character code called FIELDATA. They also had a 90-column card format with round holes, arranged in two six-row sets of 45 columns, on the same size cards as IBM used. > 5 bit Baudot was also common in the early years. There were characters to switch to numbers and figures, and back to letters. The ILLIAC I had eight-bit characters and four-bit "digits" long before the 360. For hexadecimal input from a teletype machine, in FIGS mode the digit keys produced digits with the correct binary codes. If you stayed in FIGS mode and typed KSNJFL, those keys produced "digits" ten through 15, the ones for which IBM chose to use ABCDEF. There were two mnemonics to remember this: "King Size Numbers Just For Laughs" and "Kind Souls Never Jostle Fat Ladies."
