Punched codes (original) (raw)
For computer communication one of the media was punched papertape. Here the punches in a strip of paper denoted the symbols. In Europe papertape was the dominant medium until well into the sixties. I know of five actual formats (as shown above). The only difference is the width, and hence the number of symbols that could be encoded. Papertape came in quite a few different colours, only five colours are shown here. (Note that each width was available in almost any colour.) The small holes are the "sprocket holes" that are used in feeding and in synchronisation when reading. The big holes represent the actual data. Note that the punches as shown actually represent the same message in each case, you may try to find the code used, you can also see that the 7-level and 8-level paper tapes are badly torn so that misreading at the start is quite likely. In all code pictures (except where noted) the code tables use octal numbers where the rightmost punch represents 1, the second 2, the third 4, the fourth 10, etc.
For most formats numerous codes have been in use, they are given on a number of pages, each for one of the formats:
Punched cards
Punched cards come in three forms. That the cut-off corners are shown in different position in the example has no meaning. Reading devices where not picky with respect to the position of that corner, and card variations occur with cut-off corners on either side or even none.
The first is based on the original design by Hollerith and has 12 rows by 45 columns of roundish holes. This was later expanded to the 90 column card where the upper 6 rows were for the first 45 columns and the lower 6 rows for the second 45. Coding is all binary, with lower row having a smaller number than a higher row.
Later IBM came with the 80 column punch card. The size is the same but now there are 80 columns of 12 rectangular punch positions. Although binary cards have been punched in this format, in normal coding practises not too many holes where punched in a single column. For the code table purposes the uppermost row is named Y, the next X, and the remainder from 0 to 9 (as is common). IBM came also with a 51 column card. This was only the 51 column left side part of a 80 column card. Actually I have used them for the money transfer commands for my Giro account. I had a book with 80 column cards, partly prepunched, the left (51 column) part had to be filled in (and would be punched later at the Giro office), the right part I kept as a slip.
Finally by the end of the sixties IBM came with the much smaller 96 column card. The definition has 26 rows of 32 columns with punch positions for small roundish holes. The 26 rows were divided in 6 upper rows, 2 rows that were always blank and 18 lower rows. The first 32 columns were defined by the 2 topmost rows of the upper part plus the 6 topmost rows of the lower part, giving 8 punch positions for each symbol. The remainder was defined in a similar fashion as shown in the table below. Within such a group the rows were designated from top to bottom as D, C,B, A, 8, 4, 2 and 1. The reason for this curious arrangement was the possible interpretation of the symbols on the top of the card. A symbol was only interpreted when theD and C punches were both absent, in that case on that place the symbol was printed (this allowed interpretation for the most commonly used 64 symbols). In rows 7 and 8 32 further symbols could be printed, but they would not have associated punches.
Summary of row meaning:
row columns designation
1 1-32 D
2 1-32 C
3 33-64 D
4 33-64 C
5 65-96 D
6 65-96 C
7 blank
8 blank
9 1-32 B
10 1-32 A
11 1-32 8
12 1-32 4
13 1-32 2
14 1-32 1
15 33-64 B
16 33-64 A
17 33-64 8
18 33-64 4
19 33-64 2
20 33-64 1
21 65-96 B
22 65-96 A
23 65-96 8
24 65-96 4
25 65-96 2
26 65-96 1Here are pointers to the various code tables:
Punch tags were used in the retail. A tag consisted (mostly) of two identical parts that could be teared from each other. On sale one part was left with the article, the other part was kept in the shop. Later it would be read by special equipment and the information transferred to a central computer. On the display above (based on a photograph) you see on the left a Kimball punch tag punched with a 4-level code, on the right a Dennison punch tag punched with a 2 out of 5 code. Note, normally the tags were also printed, I have omitted that because it would obliterate the view of the punches. Numerous codes did occur, the most prevalent are given on the following page: