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The mainframe turns 50, or, why the IBM System/360 launch was the dawn of enterprise IT

Joab Jackson | April 7, 2014
In 1964, mainframes weren't new, but the System/360 revolutionised the computer industry

The System/360 and its successor System/370 continued to sell well into the 1970s, as punch cards were slowly replaced by IBM 3270 terminals, known as green screens.

Green screens changed the way the System360/370 could be used. Originally, they did batch processing, where a job was submitted via punch cards. The machine would churn through the data and return the results. The green screens paved the way for more interactive sessions with a machine, noted Greg Beedy, senior principal product manager at CA and a 45-year veteran of working on mainframes.

Beedy noted that the 3270 terminals were always 80 columns wide -- equal to the number of columns on a punch card.

Even after the introduction of terminals, programming was a much more tedious job back in the 1970s; today, programmers have "instant gratification," McCoey said.

"They hit the return key and up pops an answer. That never happened. We would put together a new unit and leave it for the overnight operators to run," she said. "It would take them about 10 hours to run the test and they'd spend two or three hours to make sure everything ran correctly."

Debugging back then involved reviewing a stack of papers with nothing but hexadecimal code. McCoey would have to transcribe the code back into the routines the original programmer had devised, and then try to locate the logical error in the code.

"For me, that was a lot of fun. It was like a puzzle," McCoey said.

The programming world was also smaller then as well. Beedy started working on System/360 and similar systems in the mid-1970s, writing COBOL code for insurance companies.

"Back then, it was a tiny cult of people. Everybody knew each other, but the rest of the world didn't know what we did. It was very arcane and obscure," Beedy said. "Even the word 'software' was not that well-known. I told people I worked for a software company, they looked at me like I was crazy."

Pat Toole, Sr., one of the original System/360 engineers and later an IBM division president, observed that there were no commercial enterprise software companies, such as an SAP or Oracle, in the mainframe days. IBM supplied a few standard programs for banks, but customers also wrote their own software and it was a big undertaking.

"It was a big deal if a company spent a fortune and two or three years to write a program for a banking application, then your hardware wouldn't run it and you basically had to redo it all," Toole said.

McCoey recalled how an insurance company she once worked for when she left Sperry would run the billing program on its mainframe for the Wanamaker's department store.

 

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