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33

Yes. There were CP/CMS and VM/370 - true multiuser operating systems running on the mainframe with individual users logged in. AFAIK it was mainly used for software developers (to develop IBM mainframe software). I had the pleasure working on VM/370 once. Not what you'd call an ideal development environment. You got storage allocated to you: A certain ...


19

IBM mainframes are still around (IBM Z). Linux has been available for IBM Z hardware and its predecessor, System/390, for 20 years, and z/OS is itself a certified UNIX through the z/OS UNIX System Services. Which is to say that IBM mainframes have been run in UNIX-like multi-user fashion for two decades by running UNIX. Apart from that, z/OS and its ...


18

What is the purpose of the yellow wired panels It's the backplane, simply the wiring of the machine. on the IBM 360 Model 20? Not just there, but next to every mainframe was made that way. Depending on planned (and ordered) production run some would get printed boards, but usually all wiring was done as wire-wrap. The -20 was sold in quite high numbers ...


15

Another one to mention is MTS which was first released in 1967, last release in 1988. It was in use at Rensselaer Polytechnic Institute from 1976 to 1999, of which I took part during the early 80s. In 1984 they were running it on Sybil, a dual processor IBM 3081D; slightly before that it ran on Myron, which I think was a 3070 but I'm not sure. There were a ...


14

I found the explanation in chapters 23 and 20 of Mackenzie, Charles E, Coded Character Sets, History and Development (Addison-Wesley, 1980), which was linked in a footnote to Wikipedia's ASCII article. In the early 1960s, 7-bit ASCII was being standardized as an communication format (the last I in the name comes from "interchange"), but this does not ...


11

Why did IBM System /360 have byte addressable RAM, but didn't have 8 bits registers These issues are unrelated. Registers are about addressing, so they need to hold an address word. Byte addressable RAM in turn is needed to handle bytewide data - most notable characters and strings. There is no inherent need that a CPU must have byte sized registers as well....


11

The notation 3.2n looks to me like it means 3 x 2n rather than (3 point 2)n. So the question is whether data lengths should be based on a 6-bit unit or some 'binary' size, in practice 8 bits. The dominant character size at the time was 6 bits (with 7-bit ASCII just emerging). A 36-bit word length was also common, and was in fact the word size for the ...


9

But were any of them used like the college-lab VAX, to provide a bunch of people with interactive shell accounts that could run arbitrary code? Absolutely 100%! TL;DR University of Maryland - hundreds of simultaneous users on ASCII terminals emulating 3270 terminals for full interactive usage of email and programming. I was a student at the University of ...


9

Certainly. A place where I worked in the early 1980s had an IBM 4341 system running some species of MVS, with the TSO ('time sharing option') that supported interactive program development. I'm slightly familiar with this, since at the time I was writing a 3277 terminal emulator for VMS, and once it was good enough, the IBM sysprogs switched to that so that ...


8

Thus it was necessary or at least highly beneficial for the operating system to use memory protection to screen the users from each other ... That "memory protection" scheme is typically virtual memory. But were any of them used like the college-lab VAX, to provide a bunch of people with interactive shell accounts that could run arbitrary code? ...


8

Couldn't find much on the purpose but physically those appear to be terminals that are used for wire-wrapping. You see this application used in all manner of early electronic equipment and its used to interconnect various circuits. IBM Service technicians (customer engineers or CEs) would be the ones to actually change these (not customer serviceable). ...


8

Note that 3.2 is the square root of 10 rounded up to the closest value with one digit after the decimal. Thus, every other data length module will be slightly greater than a power of 10. Apparently there was an expectation that data block lengths will be typically close to powers of 10, achieving good capacity utilization, while providing acceptable ...


7

TL;DR: How true is this claim? It's true. While others used it before, it was the success of the /360 making it the default way around the industry. The long read: [Preface: I love the shown research] I was reading alt.folklore.computers today and found a claim: The IBM S/360 was one of the major computer systems that used 'A' to 'F' to represent a ...


6

Circa 1970, MIT's EE department operated an APL\360 virtual machine under CP/67 on an IBM 360/67. APL\360 was a multiuser dialup system for 360 mainframes, specialized for APL, but virtualizing it meant that the physical mainframe computer was shared with other users, who were mostly using CMS. So, a timeshared timesharing system. IBM's research center in ...


6

There is no downside I can see to storing an 8-bit quantity in a 32-bit register if you already have the 32-bit register. Load/store take the same amount of time. Memory transfers are at least word-sized (maybe larger) anyway. Arithmetic in general is not faster on smaller binary numbers. You'd need more opcodes or addressing modes, potentially consuming ...


5

Did any 360-compatible machine ever actually implement its registers with magnetic cores? Yes, of course, in fact, it was standard for low end machines. Beside IBM, as Ross Ridge details, many early compatible manufacturers did so. Examples are Sperry's Univac 9000 series, RCA's low end Spectra 70 models 15 and 25, or Siemens 4004/15.


5

To add to all this, System/370 with virtual memory was one of the first platforms (perhaps the third) that UNIX was ported to. You can read a paper about that porting done here. IBM would follow it up with an AIX port not long after. It was never a dominant mainframe OS, but a number of customers ran UNIX or UNIX clones on their mainframes starting in the ...


5

In the 70's I used Orvyl and Wylbur extensively on Stanford's 360/67, which Wikipedia says were originally developed in 1967-68. There were golfball terminals all over campus. Keypunched batch jobs were simultaneously being processed via card reader at the computer center.


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 ...


4

Yes To add to the UM students above we had a 7090 in the mid 60s that any student could run their own program on by submitting a punch card deck to the computer center. You picked up the print out and your cards later, often being returned to our own building where you could also have submitted them to be carried to the computer center. Later in the 60s ...


4

Wikipedia has this: https://en.wikipedia.org/wiki/Time-sharing_system_evolution IBM features heavily.


3

Yes, I had a timeshare account on my university's IBM System/360 in the early 1970s where I wrote and debugged programs in APL. The computer center had several dumb terminals that students could use for personal projects. Input was by keyboard and light pen -- no mouse. Printouts could be picked up in the printer room down the hall.


2

Did they have any performance improvements for such decision? If so, why do we have 8-bits registers today? Most 32-bit non-x86 CPU types today still only have 32-bit registers but they can access memory byte-wise. Examples are ARM, MIPS, PowerPC, Sparc, TriCore, RH850, SH CPUs and there are a lot more. So your observation is not something which is typical ...


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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