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I like to define an OS as something that can execute arbitrary binaries. So if your hypothetical Smalltalk OS has a defined executable format that non-Smalltalk

I like to define an OS as something that can execute arbitrary binaries. So if your hypothetical Smalltalk OS has a defined executable format that non-Smalltalk programs can compile to, I’d call it an OS. Note that this also makes for example the uppermost part of the JVM an OS by my definition. I’d argue it’s not a completely incorrect characterization.

eru 5y ago
I think that definition is a bit too broad and too narrow to be useful. For too narrow: you might have a security focused OS that includes everything like a TCP/IP stack etc, but perhaps doesn't allow arbitrary binaries by construction. (Eg it might only allow binaries that come with a proof of innocence, or some other restriction that's harsh enough to lose the 'arbitrary' rating.) For too broad: https://en.wikipedia.org/wiki/Weird_machine https://en.wikipedia.org/wiki/Weird_machine would make almost any software that was written sloppily enough into an OS.
- Joker_vD 5y ago
  Obviously, "capable of running arbitrary binaries, but with a check inside exec() to allow only specific binaries run" counts as "capable of running arbitrary binaries".
  - eru 5y ago
    Yes, perhaps a more specific example would be better. Imagine some embedded application, eg in car, that has a network stack, graphics drivers etc, but can only run built-in functionality.
skissane 5y ago
I don't agree that something has to be capable of running "arbitrary binaries" to count as an operating system. If I have a Smalltalk-based OS which is capable of running arbitrary Smalltalk code, but doesn't have any support for running non-Smalltalk binaries (native code or programs written in languages other than Smalltalk), I'd still consider it to be an operating system.
- deleted 5y ago
  [deleted]
- aparsons 5y ago
  The “arbitrary” part is a force of how rather than what programs are run. Is your Smalltalk code running by compiling it into the OS? Is it loaded as a library? Can I write a C backend to output an indistinguishable library? In the latter cases, it is still capable of running arbitrary code - you may just be choosing not to.
  - xkriva11 5y ago
    You can still write code in a different language like C that will compile into Smalltalk VM bytecode. You will never be able to run any arbitrary code, just the one compiled for your machine. And in this case, the machine is virtual (but does not need to be). Symbolics Lisp machines were able to run Pascal as well, for example.
ajxs 5y ago
You've presented a conscientious criterion for what can be classified as an operating system. I think it's clever, I'm not sure I agree though. It's very broad: By this same definition any processor is an operating system, since it will execute arbitrary binary data. Your example of the JVM being an operating system calls to mind the above: It is a virtual machine, it is designed to execute arbitrary bytecode in a similar manner to a processor.
- aparsons 5y ago
  You may have found a loophole in my specification :) I’d like to amend it to specify that an OS refers to software “that can run...”. (And this is why we do design reviews!). In your example, a real or virtual machine’s load/setregs interface is an operating system. One that can only run a single program at a time in the case of the physical processor’s bootstrap, but you’d be surprised how similar that is to early DOS. A more hand-waving version is “the lowest level interface over the machine that can run...”. So a processor and a ROM grid can run arbitrary programs, but the lowest common denominator entry point is the ROM flashing spec! A very slow scheduler indeed.
klyrs 5y ago
What do you mean by "arbitrary binary"? Surely, you don't mean that absolutely any binary blob should be a meaningful executable. Because that would mean that my computer doesn't have an operating system because it's only capable of running binaries built for Ubuntu on amd64 -- if your binaries targeting BSD on ARM can be viewed as "arbitrary," then surely they shouldn't be expected to run on my pseudo-operating system. No, every operating system that I know of makes some assumptions about the language that programs are written in. On my amd64/Ubuntu system, the language is largely specified by the processor (and, yes, has a binary format) and the programs are allowed to assume the presence of various devices, formats of various system calls, etc. Other languages are supported through a complicated system of compilers, interpreters and assemblers. Or, coming at a different tack: does the existence of a C->Smalltalk transpiler turn the Smalltalk-based pseudo-OS into a real OS? What if the pseudo-OS doesn't ship the transpiler, and you need to run that yourself in user-space?

eru 5y ago

I think that definition is a bit too broad and too narrow to be useful. For too narrow: you might have a security focused OS that includes everything like a TCP/IP stack etc, but perhaps doesn't allow arbitrary binaries by construction. (Eg it might only allow binaries that come with a proof of innocence, or some other restriction that's harsh enough to lose the 'arbitrary' rating.) For too broad: https://en.wikipedia.org/wiki/Weird_machine https://en.wikipedia.org/wiki/Weird_machine would make almost any software that was written sloppily enough into an OS.

Joker_vD 5y ago
Obviously, "capable of running arbitrary binaries, but with a check inside exec() to allow only specific binaries run" counts as "capable of running arbitrary binaries".
- eru 5y ago
  Yes, perhaps a more specific example would be better. Imagine some embedded application, eg in car, that has a network stack, graphics drivers etc, but can only run built-in functionality.

skissane 5y ago

I don't agree that something has to be capable of running "arbitrary binaries" to count as an operating system. If I have a Smalltalk-based OS which is capable of running arbitrary Smalltalk code, but doesn't have any support for running non-Smalltalk binaries (native code or programs written in languages other than Smalltalk), I'd still consider it to be an operating system.

deleted 5y ago
[deleted]
aparsons 5y ago
The “arbitrary” part is a force of how rather than what programs are run. Is your Smalltalk code running by compiling it into the OS? Is it loaded as a library? Can I write a C backend to output an indistinguishable library? In the latter cases, it is still capable of running arbitrary code - you may just be choosing not to.
- xkriva11 5y ago
  You can still write code in a different language like C that will compile into Smalltalk VM bytecode. You will never be able to run any arbitrary code, just the one compiled for your machine. And in this case, the machine is virtual (but does not need to be). Symbolics Lisp machines were able to run Pascal as well, for example.

ajxs 5y ago

You've presented a conscientious criterion for what can be classified as an operating system. I think it's clever, I'm not sure I agree though. It's very broad: By this same definition any processor is an operating system, since it will execute arbitrary binary data. Your example of the JVM being an operating system calls to mind the above: It is a virtual machine, it is designed to execute arbitrary bytecode in a similar manner to a processor.

aparsons 5y ago
You may have found a loophole in my specification :) I’d like to amend it to specify that an OS refers to software “that can run...”. (And this is why we do design reviews!). In your example, a real or virtual machine’s load/setregs interface is an operating system. One that can only run a single program at a time in the case of the physical processor’s bootstrap, but you’d be surprised how similar that is to early DOS. A more hand-waving version is “the lowest level interface over the machine that can run...”. So a processor and a ROM grid can run arbitrary programs, but the lowest common denominator entry point is the ROM flashing spec! A very slow scheduler indeed.

klyrs 5y ago

What do you mean by "arbitrary binary"? Surely, you don't mean that absolutely any binary blob should be a meaningful executable. Because that would mean that my computer doesn't have an operating system because it's only capable of running binaries built for Ubuntu on amd64 -- if your binaries targeting BSD on ARM can be viewed as "arbitrary," then surely they shouldn't be expected to run on my pseudo-operating system. No, every operating system that I know of makes some assumptions about the language that programs are written in. On my amd64/Ubuntu system, the language is largely specified by the processor (and, yes, has a binary format) and the programs are allowed to assume the presence of various devices, formats of various system calls, etc. Other languages are supported through a complicated system of compilers, interpreters and assemblers. Or, coming at a different tack: does the existence of a C->Smalltalk transpiler turn the Smalltalk-based pseudo-OS into a real OS? What if the pseudo-OS doesn't ship the transpiler, and you need to run that yourself in user-space?