2.1 The mainframe's birth
Before 1940, a "computer" was a human being who did calculations using paper and pencil. Digital or electronic computers were developed to relieve the human computer of boring, iterative calculation work. An electronic computer performed calculations much faster than a human could and did not get tired. An important aspect of the electronic computer was that it could store a program. This distinguished the computer from an adding machine.
The first electronic computers were housed in several cabinets consisting of steel frames with metal covers. The most important cabinet the main frame housed the circuitry that performed calculations. The other cabinets housed power units and peripheral devices such as tape drives.
The very first IBM mainframe was installed half a century ago in IBM world headquarters (see Figure 2-1). It consisted of a room-sized set of cabinets housing the units for the 701 Defense Calculator. The 701 was the first large-scale, high-speed, stored-program electronic computer to be produced in volume by IBM.
Figure 2-1. The room-sized 701, IBM's first mainframe. IBM announced installation of the first machine in 1953. The 701 main frame is at the back of the room on the right. The other cabinets include three power units, a dual magnetic tape drive to the left, and card units to the right. (Photograph courtesy of IBM Archives.)
The 701 was capable of performing thousands of instructions per second: 2000 instructions when multiplying and dividing, and up to 16,000 when adding and subtracting. The average instruction execution rate was 14,000 instructions per second. Compared to the manual computing common at the time, this was an overwhelming achievement. One day of digital computer time was equivalent to 500 years of pencil and paper calculations.
The 701 may have been the first large-scale electronic mainframe, but it was built for special engineering and scientific purposes, not for commercial transaction processing. It did not have a general-purpose operating system (OS), and it could run only custom-made programs. However, its success encouraged IBM to make a computer for the commercial market. To find all-purpose mainframes as we know them today, we must go forward to the 1960s.