Retrotechtacular: Card Programming

The recent Supercon 6 badge, if you haven't seen it, was an old-fashioned type computer with a flashing bright front panel. It was reminiscent of an Altair 8800, PDP-11 or DG Nova. However, even back then, only a few people really programmed a computer with switches. Typically, you can use the switches to switch into a first-level bootloader which would then load a better bootloader from some type of storage such as tape or paper. Most people didn't really use switches.

What most people did, however, was punch cards. Technically Hollerith cards, although we mostly call them cards, punch cards, or IBM cards. There were lots of different machines you could use to punch cards, but none were as popular I guess as the IBM 029. Certainly the models in the series were overwhelmingly what people used to punch cards.

For the uninitiated, a card was about the size of an old-fashioned dollar bill - the ones that were all the rage when Herman Hollerith invented them. The card was made of a material not as thick as a standard folder and was divided into 80 columns and 12 rows. Later maps had more columns, but these never quite reached the same scale as the classic 80-column map.

To punch a number on the card, a machine punched a hole in one of the bottom 10 columns. So a hole in row "1" was a 1 and a hole in row "4" was a 4. The original cards used round holes and 45 columns, but an IBM inventor named Lake realized that narrow square holes could pack more data dates back to 1928. The 11th and 12th lines, and sometimes the "0" line, were used to denote special characters or, sometimes, the signs of numbers.

A deck with a "sorting strip" by ArnoldReinhold, CC-BY-SA-3.0
Honestly, you could interpret a card however you wanted, but in practice there were a few common patterns. However, it was not unheard of to have punch cards in binary where each hole was a 1 or a 0 and each column constituted a binary number. In addition to character encoding, there were other format conventions, such as having checksums or row numbers in certain columns of the map. Line numbers, in particular, were good because they let you sort out a game after it was dropped and the order was scrambled. Another common trick was to draw a diagonal marker line across the edge of a deck of cards so you could quickly spot if one or more were down.

Blank cards were often used as a "sentinel" or what we would today call an "end of file" marker. However, some programs would look for an impossible value like -9999999, for example.
While reading
A card reader was relatively simple. Most readers used a series of wire brushes under which the map moved. Where there was a hole, the brush could come into contact with a metal plate under the board and complete a circuit. If that doesn't sound very reliable, that's because it wasn't.

The old "do not bend, pin, or mutilate" warning was a request for users not to jam cards on machines or punch new holes in them. A pin, if you don't remember, was probably a non-OSHA compliant spike on your desk that you pushed papers over to hold them in place. Not a good strategy for a punch card.

In fact, a common prank was to punch out each column of a card so that it...

Technology Nov 10, 2022 0 46 Add to Reading List

The recent Supercon 6 badge, if you haven't seen it, was an old-fashioned type computer with a flashing bright front panel. It was reminiscent of an Altair 8800, PDP-11 or DG Nova. However, even back then, only a few people really programmed a computer with switches. Typically, you can use the switches to switch into a first-level bootloader which would then load a better bootloader from some type of storage such as tape or paper. Most people didn't really use switches.

What most people did, however, was punch cards. Technically Hollerith cards, although we mostly call them cards, punch cards, or IBM cards. There were lots of different machines you could use to punch cards, but none were as popular I guess as the IBM 029. Certainly the models in the series were overwhelmingly what people used to punch cards.

For the uninitiated, a card was about the size of an old-fashioned dollar bill - the ones that were all the rage when Herman Hollerith invented them. The card was made of a material not as thick as a standard folder and was divided into 80 columns and 12 rows. Later maps had more columns, but these never quite reached the same scale as the classic 80-column map.

To punch a number on the card, a machine punched a hole in one of the bottom 10 columns. So a hole in row "1" was a 1 and a hole in row "4" was a 4. The original cards used round holes and 45 columns, but an IBM inventor named Lake realized that narrow square holes could pack more data dates back to 1928. The 11th and 12th lines, and sometimes the "0" line, were used to denote special characters or, sometimes, the signs of numbers.

Honestly, you could interpret a card however you wanted, but in practice there were a few common patterns. However, it was not unheard of to have punch cards in binary where each hole was a 1 or a 0 and each column constituted a binary number. In addition to character encoding, there were other format conventions, such as having checksums or row numbers in certain columns of the map. Line numbers, in particular, were good because they let you sort out a game after it was dropped and the order was scrambled. Another common trick was to draw a diagonal marker line across the edge of a deck of cards so you could quickly spot if one or more were down.

Blank cards were often used as a "sentinel" or what we would today call an "end of file" marker. However, some programs would look for an impossible value like -9999999, for example.

While reading

A card reader was relatively simple. Most readers used a series of wire brushes under which the map moved. Where there was a hole, the brush could come into contact with a metal plate under the board and complete a circuit. If that doesn't sound very reliable, that's because it wasn't.

The old "do not bend, pin, or mutilate" warning was a request for users not to jam cards on machines or punch new holes in them. A pin, if you don't remember, was probably a non-OSHA compliant spike on your desk that you pushed papers over to hold them in place. Not a good strategy for a punch card.

In fact, a common prank was to punch out each column of a card so that it...