Gentlefolk,
SinBin had become confused with bits and bytes so I thought a practical illustration might help. That led me on to some historical ramblings which are posted below the link to a photograph of paper tape.
Kind regards,
Walter
http://www.scribd.com/Unipunch-Open-amp-Paper-Tape-2265/d/30540707The picture shows a unipunch with the retaining lid off, a section of paper tape and an adhesive patch used to repair torn tape.
The paper tape has 8 holes across it, sometimes known as channels, plus a sprocket hole which was originally used to pull the tape through the automatic punch and then the tape reader. Latterly it was used in optical or capacitive readers as the strobe to read the paper tape character or byte. i.e. a row of holes.
To recap one hole is a digital bit and a row of 8 bits make one byte. The least significant or low order bit is on the right and the most significant or high order bit is on the left. In a binary word, the bits have increasing values from right to left of 1, 2, 4, 8, 16, 32, 64,128.
So reading the set of bytes near the patch the top row represents the digit 1, the next 2, the third 3 and the fourth 4 etc. so you now know how to convert binary to decimal !
Paper tape was also used to enter alpha-numeric data according to a standard code. The one illustrated in the top two groups is American Standard Code for Information Interchange or ASCII, pronounced askey. In this illustration bit 8 is always added to make every character even parity, i.e. bit 8 is added to every character which would otherwise have an odd number of bits. Bits 6 and 7 are used to differentiate between upper case, lower case and numeric characters. The centre group starting at the top represent the upper case characters A, B, C, D & E. The top group are the numbers zero to 9. The “all ones” character was the delete or null character so you could blot out an error. At this time there were no editors available so source code tapes in ASCII were edited by running the tape through a teleprinter reader and punching a new tape at the same time. Where a change was required the input tape was stopped, new characters were punched into the output tape from the keyboard, and the old tape was then pulled through to the point where the rest of the data was correct again. I wrote probably one of the first computer tape editors in the UK on a radar system using its tabular display. Later when floppy disks and then hard discs with a staggering capacity of 2.4 Mbytes were introduced, proper editors used a teleprinter keyboard for the editing commands such as C/JACK/FRED to change the first occurrence of JACK to FRED from where the cursor was. To find the names of the files within a folder it had to be printed out using a command such as
TI:=DK3:[154,154]*.*/LI i.e. list to the console the contents of disk 3’s User Identification Code 154,154 all file names with all version numbers.
Although very high speed tapes were used in Bletchley Park, the industry norm was 1000 characters (or 10 Inches of tape) every second. So the maximum data input speed of the tape reader was 8000 bits per second.
This was the technology in use towards the late 1960s. Before that, standard GPO teleprinters were used with 5 channel tape I think with a maximum speed of 10 characters per second. With only 5 channels it was not possible to produce even a full alphabet with the numbers and some basic punctuation. Two precious characters were used for case normal and case shift which provided a workable letter vocabulary. The printers often produced nonsense on incoming messages so the trick was to punch a tape from the incoming message, replay it and then inch the tape forward before adding a case normal or shift from the teleprinter keyboard.