IBM 370 Computer Is First Virtual Machine (Great Events: 1900-2001)
Article abstract: The International Business Machines (IBM) 370’s new memory and machine structure increased the effectiveness and multiuser capabilities of computers without increasing costs prohibitively.
A Shortage of Memory
During the late 1950’s and the 1960’s, computers generally used two types of data storage areas. The first type, called “magnetic disk storage,” was slow and large, but its storage space was relatively cheap and abundant. The second type, called “main memory” (also often called “random access memory,” or RAM), was much faster. Computation and program execution occurred primarily in the “central processing unit” (CPU), which is the “brain” of the computer. The CPU accessed RAM as an area in which to perform intermediate computations, store data, and store program instructions.
To run programs, users went through a lengthy process. At that time, keyboards with monitors that allowed on-line editing and program storage were very rare. Instead, most users used typewriter-like devices to type their programs or text on paper cards. Holding decks of such cards, users waited in lines to use card readers. The cards were read and returned to the user, and the programs were scheduled to run later. Hours later or even overnight, the output of each program was printed in some predetermined order, after which all the outputs were placed in user bins. It might take as long...
(The entire section is 1131 words.)
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