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The XT/370 microprocessor: System/370 instructions microcoded in a 68000

IBM System/370 – 1970
IBM introduced the 12.5MHz cabinet sized System/370 in June 1970 as an evolution of the System/360 from 1964.  These systems formed the entire base of IBM’s mainframe business.  Today’s System z, itself an evolution of the original System/360 and 370, can still run many of the original programs, unmodified, from 50 years ago.  This is a testament to 2 things, the wide adoption of the IBM systems, and the forward thinking of IBM.  Even the original System/360 from 1964 was a full 32-bit computer.  Single chip processors did not embrace 32 bit architectures until the very early 1980’s (Motorola 68k, National 32k, etc).
In 1980 IBM sought to make a single chip version of the 370, in an effort to make a version that could be used for desktop type computers.  This was to become the Micro/370.  There were 2 distinct products to come out of this goal that are


 

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