HISTORY OF COMPUTERS - continued (PREV) (PAGE 1)
IBM introduced a smaller, more affordable computer in 1954 that proved very popular. The IBM 650 weighed over 900 kg, the attached power supply weighed around 1350 kg and both were held in separate cabinets of roughly 1.5 meters by 0.9 meters by 1.8 meters.

It cost $500,000 or could be leased for $3,500 a month. Its drum memory was originally only 2000 ten-digit words, and required arcane programming for efficient computing. Memory limitations such as this were to dominate programming for decades afterward, until the evolution of hardware capabilities and a programming model that were more sympathetic to software development.

In 1955, Maurice Wilkes invented microprogramming, which was later widely used in the CPUs and floating-point units of mainframe and other computers, such as the IBM 360 series. Microprogramming allows the base instruction set to be defined or extended by built-in programs (now sometimes called firmware, microcode, or millicode).
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