Later On

A blog written for those whose interests more or less match mine.

Blast from the past: Doing fractals with the IBM 1401

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I spent some years writing programs for the IBM 1401 computer. We wrote in assembly language using pencils and coding forms, which were sent to the keypunch department to be punched into cards. The punched cards were then used as input to the Autocoder program to be translated to machine language; Autocoder then punched out a loadable program deck. When you put that deck into the card reader and pushed start, the first card was read, which included instructions to read the next card, and so on. The cards also had instructions to load the machine code in the cards into memory at the appropriate locations. A complex program might take an entire box of cards (2000 cards), but most were probably around 300-1000 cards.

Those were the days. This article describes the fractal program and also a fair amount of the 1401 hardware. The description of the Binary-Coded Decimal (BCD) are spot-on. God, I knew all that stuff by heart. Takes me back.

There were two versions of the Autocoder program that converted the assembly-language punched cards into a loadable machine-language card deck (a deck much smaller than the assembly-language deck): two-tape Autocoder (which used two tape drives—this was long before disk storage) and four-table Autocoder (requires four tape drives, and naturally this was the official IBM version, since it required the rental of more tape drives—and back then IBM would not sell any equipment: it was all leased (to create a continuing revenue stream).

Some good photos at the link.

Written by LeisureGuy

27 March 2015 at 1:46 pm

Posted in Business, Techie toys

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