What was the use case for the 96-column punch cards introduced with the IBM System/3?
About the same as for introduction of 5.25 or later 3.5 inch floppies: same capacity in a smaller form factor. In fact, the 96 column card was kind of the 3.5 of punch cards, just right to be put in a shirt pocket.
So ... why did IBM invent them,
To give more storage in smaller space to improve handling of small to medium data sets. A 96 column card was only about 1/3rd the size of a standard card but could hold 20% more information, so that's almost quadrupling data density.
Of course, when just looking at the increased storage capacity, one could as well have used the existing format and tripple data density. But to use this software would have to know that cards now three times as large. But 80 columns was deeply engraved into the very foundation o all databases at the time. Changing all of that would have been an incredible task.
Making the card smaller on the other hand would bring the same improvement while being mostly compatible on the software side. A 96 column card can quite well be used by software expecting (and producing) 80 column cards. It would simply not see the additional 16 columns while on output they stay empty.
No changes handling required but an immediate save of 66% storage space.
and at that time?
Time is maybe the most important item here. The System 3 was developed in the late 1960s - introduced 1969 - right at a time when punch cards were still a thing but started to become more and more obsolete due tapes and disks.
It was almost as if Volkswagen would today introduce a whole new (*1) gas engine design. It would be awesome tech and great engineering, but vanish faster than its predecessors as we're moving toward electric propulsion.
In fact, essentially the same happened with the 96 column card. it got introduced in 1969 with the IBM 5424 Multifunction Card Unit (MFCU) and replaced starting in 1973 by the IBM 3741 floppy units. First as add-ons to existing machines, later the MFCU was no longer offered, so 3740 floppies became the way to handle small data sets (*2).
As history goes, the 80 column card survived a bit longer due its massive instalment base.
Before the System /3 there was the System 3000
The 96 column card (like the system /3) didn't appear out of nowhere but is based on the System 3000 design developed in Böblingen in the early 1960s. The System 3000 was intended as a very low end machine. It introduced an 240 column punch card half the size of the standard one, to be seen on the left side of this picture:
Left Side: 'half' length, 240 character System 3000 cards
Right Side: 'third' length, 96 character System /3 cards
(image taken from here)
This half size 240 column card shows already all features of the later 96 column card (shown above on the right side):
- Encoding (see below) of three characters within a column
- as 4 groups of 6 holes
- three of them holding a character each
- the fourth combining two 'overflow' bits per character if needed
The system 3000 suffered from problems with its card devices (and possibly a certain 'not invented here' syndrome in Rochester).
Rebirth as 96 column card
While the System 3000 was cancelled in 1964 (?), the idea of a smaller, more capable punch card lived on. In fact, the System /3's 96 column card follows the System 3000'S card in all but mechanical definition. While being smaller, it had only 32 physical columns, spaced wider than the System 3000 card but at the same time with smaller holes. It's safe that this was to get around the mechanical problems that killed the System 3000.
The restriction to 96 characters on the other hand added a high compatibility layer with classic cards, as all handling coudl be kept fully compatible with 80 column cards.
How to encode 3 characters in 4 groups of 6 holes
Both cards used a modified EBCDIC code with full 8 bit encoding as seen here:
(Table taken from this incredible useful page)
- The holes are numbered
- Of these the lower 6 (1..B) are punched into every character cell
- The holes for CD of each character cell are combined into the top 6 hole group.
This seems to be a quite odd scheme until we consider that punch cards had as well writing along the top row(s). The first 64 character encoding (framed in blue) will have only no holes in C or D, thus leave the top area unharmed. By arranging all basic letters (only upper case), numbers and symbols within these 64 codes chances are high that most cards will have no hole within the upper fourth of the card. Perfect for undisturbed labeling. Isn't it?
*1 - As in 'real new super high tech 30% more efficient'
*2 - Noteworthy again that the floppy did only play a small role here as it eliminated the use case for small data sets. Even before floppies disks and tapes did successfully start to replace punch cards for large data sets. so to floppy just killed the last niche for punch cards, and even an improved one couldn't hold much against that.