6 ms·

Incidentally, I just finished reading "The Mythical Man-Month", which also discusses another old large system, IBM System/360 and its operating system OS/360.

Incidentally, I just finished reading "The Mythical Man-Month", which also discusses another old large system, IBM System/360 and its operating system OS/360. It's really interesting to see how current the discussions on these old machines can be. From the OP: "For additional security, code and data were distinguished in memory by the use of a "flag bit", and the hardware would not execute data or alter code without first having explicitly changed the flag" We've been dealing with buffer-overruns and code injection in the stack until very very recently, and there are surely machines out there that still don't have support for the NX bit. We surely still have a lot to learn from the past.

mikestew 13y ago
What was it, _South Park_ that did the "Simpsons did it" episode? Thinking about some of the things that came along 20 or 30 years later remind of that. Virtual machines? OS/360 did it. Virtual memory? OS/360 did it. Non-executable data? OS/360 did it. I was a security lead for a product while at Microsoft when the NX was being implemented, and wondered at the time why it took 35 years to get around to that. (I've never worked on a 360, but did some work its successor the 370 and OS/370 some many years ago.) Even the Burroughs had multitasking before then, in the early 60s. And how can you not like a system with a "HEYU" instruction to interrupt other processors?
- da02 13y ago
  Ever get an answer, or come close to one, as to why it took 35 years?
  - cliffbean 13y ago
    Before the Internet arrived, very few people had a big need for it. It makes some things marginally harder, and it's more work to implement, so it makes sense that it got left off. By the time the Internet generally arrived, and people generally realized what the Internet meant, we had accumulated enough backwards compatibility burden that sweeping architectural changes were difficult.
  - mikestew 13y ago
    Never had access to those that could give an informed answer. As cliffban says, probably not much of a need. But if I had to pick a reason, and it would be a reason based on no inside knowledge, it's that the 8086 was a stop-gap design until the Intel iAPX 432 came out. The 432 had a lot of capabilities that mainframes took for granted, including segregation between data and executable code. Problem was that the 432 was so over-designed (which made it slow, for one problem) that it never saw production. So everyone just kind of settled on x86 and close to forty years later we're stuck with the 8086 legacy.
derefr 13y ago
Microprocessors were one of those "disruptive" innovations, in that their architectures mostly threw out the previous 30 years of good Engineering design ideas in order to give customers something cheap and immediately useful. Oddly, it's taken another 30 years for microprocessors to reabsorb those ideas.
- Taniwha 13y ago
  I disagree - I was a B6700 hack, loved the machine - but code for it was just so non-portable because the machine model was just so non-standard - remember this is a machine (B5000 et al) that depended on the compiler creating correct and sane code not just for system security but system integrity - only 'root' could write compilers and one bad instruction would take the entire system down - it was fragile. Microprocessors when they first came out were also feeling their way into architecture, Intel sort of headed down the Burroughs tagged capability architecture route - 286 segments, the 960, the 432 et al But in the long term the PDP11/Vax were more the machines that people loved and their simple memory model (a simple array of bytes) and generic identical registers allowed portable languages and operating systems to flourish - prior to this operating systems were designed for particular hardware platforms - Burroughs MCP was never going to run on any other machine. People forget that the idea of a portable operating system in a time where operating systems were written and were the closed property of hardware manufacturers was a pretty radical idea at the time. RISC, where simple was beautiful, loved the simple memory/execution models, Unix having grown up on PDP11s and Vaxen was the same. Intel's through this was bit of a weird duck - they tried everything and failed at many of them - the CISCiest thing imaginable (the 432 a true capability machine) and the 960/860 (both kind of RISCy) all appeared at about the same time - but the 'x86 architecture has walked a pretty magically fine line - in a time of VAX derived CISCy architectures (68k 32k etc) they had a relatively simple memory addressing model (no indirect stuff) and a pretty simply instruction set - in retrospect much more RISCY than it's contemporaries, though missing the generic register file, the 386 eventually adopted the simple linear memory model and tried to forget about all that silly segment stuff and the 64-bit instruction set has moved to a RISCy world - I used to really hate the x86, especially when I wrote compilers, but in retrospect it's mellowed The thing that microprocessors and the architectural trends they adopted have really done is they've taken us from a proprietary world where nothing was portable, where once you'd bought a system you were a captive customer - to a marketplace with competitive manufacturing and happier consumers

mikestew 13y ago

What was it, _South Park_ that did the "Simpsons did it" episode? Thinking about some of the things that came along 20 or 30 years later remind of that. Virtual machines? OS/360 did it. Virtual memory? OS/360 did it. Non-executable data? OS/360 did it. I was a security lead for a product while at Microsoft when the NX was being implemented, and wondered at the time why it took 35 years to get around to that. (I've never worked on a 360, but did some work its successor the 370 and OS/370 some many years ago.) Even the Burroughs had multitasking before then, in the early 60s. And how can you not like a system with a "HEYU" instruction to interrupt other processors?

da02 13y ago
Ever get an answer, or come close to one, as to why it took 35 years?
- cliffbean 13y ago
  Before the Internet arrived, very few people had a big need for it. It makes some things marginally harder, and it's more work to implement, so it makes sense that it got left off. By the time the Internet generally arrived, and people generally realized what the Internet meant, we had accumulated enough backwards compatibility burden that sweeping architectural changes were difficult.
- mikestew 13y ago
  Never had access to those that could give an informed answer. As cliffban says, probably not much of a need. But if I had to pick a reason, and it would be a reason based on no inside knowledge, it's that the 8086 was a stop-gap design until the Intel iAPX 432 came out. The 432 had a lot of capabilities that mainframes took for granted, including segregation between data and executable code. Problem was that the 432 was so over-designed (which made it slow, for one problem) that it never saw production. So everyone just kind of settled on x86 and close to forty years later we're stuck with the 8086 legacy.

derefr 13y ago

Microprocessors were one of those "disruptive" innovations, in that their architectures mostly threw out the previous 30 years of good Engineering design ideas in order to give customers something cheap and immediately useful. Oddly, it's taken another 30 years for microprocessors to reabsorb those ideas.

Taniwha 13y ago
I disagree - I was a B6700 hack, loved the machine - but code for it was just so non-portable because the machine model was just so non-standard - remember this is a machine (B5000 et al) that depended on the compiler creating correct and sane code not just for system security but system integrity - only 'root' could write compilers and one bad instruction would take the entire system down - it was fragile. Microprocessors when they first came out were also feeling their way into architecture, Intel sort of headed down the Burroughs tagged capability architecture route - 286 segments, the 960, the 432 et al But in the long term the PDP11/Vax were more the machines that people loved and their simple memory model (a simple array of bytes) and generic identical registers allowed portable languages and operating systems to flourish - prior to this operating systems were designed for particular hardware platforms - Burroughs MCP was never going to run on any other machine. People forget that the idea of a portable operating system in a time where operating systems were written and were the closed property of hardware manufacturers was a pretty radical idea at the time. RISC, where simple was beautiful, loved the simple memory/execution models, Unix having grown up on PDP11s and Vaxen was the same. Intel's through this was bit of a weird duck - they tried everything and failed at many of them - the CISCiest thing imaginable (the 432 a true capability machine) and the 960/860 (both kind of RISCy) all appeared at about the same time - but the 'x86 architecture has walked a pretty magically fine line - in a time of VAX derived CISCy architectures (68k 32k etc) they had a relatively simple memory addressing model (no indirect stuff) and a pretty simply instruction set - in retrospect much more RISCY than it's contemporaries, though missing the generic register file, the 386 eventually adopted the simple linear memory model and tried to forget about all that silly segment stuff and the 64-bit instruction set has moved to a RISCy world - I used to really hate the x86, especially when I wrote compilers, but in retrospect it's mellowed The thing that microprocessors and the architectural trends they adopted have really done is they've taken us from a proprietary world where nothing was portable, where once you'd bought a system you were a captive customer - to a marketplace with competitive manufacturing and happier consumers