Once upon a time there were no cheap personal computers, which made storing data and looking up information really slow. But there was a solution: notched edge cards. Much of the terminology and techniques for these cards were borrowed from expensive mechanical technology used by regular punch cards.
But what is a notched edge card? Imagine a stiff piece of card with nice small round holes punched in the edges. A handheld punch—which looked like the punches used at one time for various paper tickets—can be used to turn a hole on the edge of the card into a notch, hence the name of the cards.
A punch card, ready to store one line of Fortran77
Once all the notch making is done, the cards are stacked in a deck. Borrowing a trick from punch cards, the upper right hand corner of each card is usually clipped off, allowing you to more easily make sure that all of the cards in a deck are facing the same way.
Long metal ‘knitting needles’ can then be inserted through the holes. With a little shaking, the needle is lifted up, and the cards that did not have a notch lift out on the needle. The notched cards are squared off and put in front of the unnotched cards. This process can be repeated with multiple holes, and at the end the cards with the same pattern of notches on their edges will be grouped together. With a little practice, anyone can quickly put the deck in sorted order.
This technology would not have been good for a very large database, but for several hundred cards it was wonderful. It required no expensive equipment or even electricity! The handheld notching punches originally cost less than around £5 each, and you can still find them for around £10. The original sorting needles had wooden and later plastic handles; these handles are not really needed, but can easily be replaced with handles from the hardware shop tool section.
When the notched edge cards were popular, and being used by larger commercial enterprises, there were some other tools available. There was a bulk notch tool, which could clip a notch in the same place in several hundred cards at once—think of it as a specialised office paper cutter. There was a vibrating platform which could help stack and square off a deck of notched edge cards. But the most interesting and rare piece of hardware was the card punch from the Royal McBee company for their Keysort cards. You could not buy one and instead had to rent it from the company, a practice started by IBM for the early unit record—that’s what we called punch cards back then—equipment.
A McBee Keysort B86791X card, designed for storing data about birds in South America
One notched edge card is placed in a slot at the top of the punch, and below that are several columns of buttons. The keys in each column were numbered $7, 4, 2, 1$. The operator pushed down these keys which locked in place. When the operator was happy with the configuration of punches they had encoded for that edge, they pulled the lever on the side the device, and all the punches came up and notched the columns on that edge of the card in a single stroke. You proceeded in this fashion with the rest of the cards in the deck. When you had finished one edge, you could rotate the cards to notch the holes on the next edge.
Many of the early adding machines also had this particular mechanical design: you push down keys to input the numbers you wanted to add, then pulled the lever and that number was printed on a continuous roll of paper. By throwing some other switches, you could get the total output onto the paper.
The best selling brand was the McBee Keysort, probably because they came up with the support devices that I just discussed and they pre-printed cards for common business applications. For example, it was possible to get blank multipart cheques pre-printed and pre-punched. This meant that a small business could reconcile its cheques without buying expensive tabulating equipment.
Keysort cards became immensely popular for public schools and small-town libraries in the United States. They also gained popularity for military occupational specialties in the US army, record keeping in the US forestry service and other locations that did not have a lot of electrical outlets or big budgets.
There were also notched edge cards that had space in the centre for microfiche—a photographic technique that takes very small pictures of documents to save storage space and speed up access. By mounting them on a notch edge card, the operator could quickly find any given document they desired. I’d like to remind you the technologies I’m discussing are very old, so don’t be too judgmental—but these cards were still in use into the mid- and late 1960s.
Encoding systems
The simplest way to encode digits on notched edge card was group four holes into what was called a field. Within the field, the holes represent the values $7, 4, 2$ and $1$ from left to right. To store a digit in a field, you simply notched one or two holes. You stored a value of $3$ by notching both $2$ and $1$. Likewise, $5=4+1$, $6=4+2$, $8=7+1$ and finally $9=7+2$. It is possible to store a $7$ by notching $4, 2$ and $1$ (instead of just notching the $7$), but this involves three columns and physically weakens the card, so was avoided. Likewise, you could store some numbers larger than 9 by notching more than two holes, but since we use a base 10 number system it was more convenient to store each digit of a number separately.
Letters can also be done in two punches each. The trick is that some combinations will represent multiple letters, much like you see on some paper index products which will have ‘XYZ’ on a single tab.
Finally, we could use what was originally called a superimposed code. The most popular of these was known as Zatocoding, but today is referred to as hashing and we have a better understanding of the mathematics behind it. While the encoding of letters and digits was relatively standard, each of these hashes was unique to the set of data we were trying to index, and required a copy of the key to the hash. It’s still a good technique though, especially if you have a small data set that’s relatively static (notice that the definitions of ‘small’ and ‘ static’ have changed a good bit since this technology was popular).
Making cards
If you want to make your own card database, it’s not too hard to get hold of what you need. Knitting needles that can be used as sorting needles are easy to get from any craft shop. Notching punches can be found on eBay, or you might get lucky and find them in an office supplier, maybe sold as a ticket punch. Getting the cards themselves is the real challenge.
I recommend finding a print shop that does wire spiral binding: the punch they use to make the holes for the spiral bind often makes circular holes around the right size and distances apart. You’ll want to print on your cards before sending them to the bindery: it’s hard to print pages that have already been punched.
I hope you get a chance to play with this technology and it gives you some incentive to read about the history of early computing equipment.
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