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38

there some particular design theory or constraint that made a 32-bit word size attractive for IBM to migrate to? It all comes down to the most basic data type, addressing constrains and, less important, reuse of existing memory technology. The byte size had to be a multiple of 4, as needed to accommodate BCD numbers without wasting space. So 8 was chosen ...


6

One small reason is that you can access memory as a bit array without needing to divide (or do a modulo). Just use the bottom N bits for the byte or word or data cache line position or shift, and the rest of the bits left over as a memory address offset. Which can be done in hardware for free if needed.


5

Worthy of mention is the rise of the microprocessor- notably the 4004 which was designed for mostly numerical operation in calculators. Whether the step to 8 bit architecture was inevitable is open to debate, but once memory ICs started being produced in 8-bit forms, it would be difficult to justify anything other than 16-bit as the next step. Looking at ...


5

The University of Cambridge (UK) Computing Service acquired a 370 around 1972 at the time I was starting my Ph.D, and operated it as a time-sharing service. Using experience from the Titan operating system, they pretty well rewrote the system (it was unusable out of the box). Particular features I recall were the job scheduler devised by John Larmouth, which ...


3

TL;DR: The IBM 7030's fixed-point arithmetic model was unusual: binary numbers could have any number of bits from 1-64. Similarly, PL/I's FIXED BINARY data type has a variable number of bits. Coincidence. PL/1 simply uses an abstract, non machine specific way to define the entities it handles - like any good HLL should do. System/360, with its now-...


2

Most large System/360 and System/370 installations were multiuser. I never saw a University whose S/360 or S/370 was not multiuser, and I never worked on a machine larger than a 360/50I that was not multiuser. CP-67, TSO and VM were common, to say nothing of the services running multi-user APL software. As for single threading command interpretation, that ...


2

Lots of good information here but as an ex-MVS sysprog I would like to approach it from a different direction. The MVS/370 operating system (Multiple Virtual Storage on 370 architecture) was an OS that could provide virtual address spaces to a large number of users. Although not directly equivalent think of an address space as being like a Unix process and ...


2

Many answers mention interactive timesharing systems, but, even in a purely batch environment, there would typically be multiple jobs (i.e. processes) loaded into main memory at once and the CPU would switch between them. The reason was efficiency. If you have one job that had to stop and wait for, say, a tape to be mounted, you'd want the CPU to switch to ...


1

CTSS at MIT was one of the first timesharing systems ever built. It ran on a modified IBM 7094 mainframe. This is from the 1963-1966 time frame. Memory protection was extremely primitive. There were two banks of memory, one for the system and the other for the current user. The user program could only clobber its own memory. Users could develop programs ...


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