IBM 1401 Starting by LaFarr Stuart

Last Up date: 2006 November 2
This Web Page started: 2006 November 2

Of the early "Real Computers" (computers that had nothing dependable in memory when they were powered up) the 1401 was by far the most elegant.

The 1401 had a Load Button on the console; but there was a duplicate one on the Card Reader. The Load Buttons were back illuminated and always "Yellow". Pressing either of these:

  1. Cleared the first 100 locations of memory
  2. Read a card into locations 1 through 80
  3. Started running at location 1
The first 4 characters punched into that card had to be: ,008 because every op-code had to have a Word Mark set. The comma was the command that set the word mark. See More about the 1401 and its features. These 4 characters were followed by 3 more characters. The "set word mark command" could set two word marks. Making this instruction 7 characters long. Thus, the next instruction was at location 008. I believe set word mark is the only command that does not have to have a word mark with the first character following it. Generally, at least another "set word mark command" followed. In an 80 column card you could get a few instructions and of course another card read. Incidentally, the card read instruction could be only one character--the digit 1, but if it were followed by a 3 character address, it would read and branch to that address. With this the 1401 was off and running.


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