Monday, May 18, 2009

80 Column Punched Cards and the History of RPG on the AS400

An article where Jon Paris discusses the lineage of punched cards that leads to RPG and the as400...

Anyway it got me thinking about how little many of us know of our own history as it relates to the IT industry. Would you believe that there are people out there who actually believe that Bill Gates and Microsoft invented the concept of a windowing GUI! They probably believe they invented DOS too--poor misguided souls.

On the subject of punch cards, let's take a quick look at how they impacted our favorite language--RPG. Since some of you may not have actually seen a punch card before, here's a picture of one so that we all know of which we speak:

rpg punched card as400

As you can see there are 80 vertical columns, which explains the 80-column limit in RPG II and RPG III. You might also have wondered why the first five columns of the spec are designated as the sequence number. Well, suppose you had a 600-line RPG program and it was on punch cards. Now suppose that you dropped the box and 600 cards hit the floor. How long do you think it would take you to put the program back in order? Now you understand the reason for the sequence number.

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