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Software interrupt?

The text A software interrupt (also known as a signal) is a notification to a process that an event has occurred. Whereas a user process can send signals to other user processes and even to itself, signals are usually sent from the kernel.in #Software interrupt conflicts with Interrupt#Software interrupts. External events such as expiration of time slice, IPC signals and keyboard signals from the user do not fit the definition in Interrupt#Software interrupts, nor have I seen the term applied that way in any OS. Also, there is no text describing how various operating systems handle various types of interrupts.

I propose that the introduction be replaced by the text in Interrupt#Software interrupts and that subsections be added describing sample scenarios in various operating systems. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 11:14, 25 April 2022 (UTC)

• I'm an avid student of how computers work. So, I welcome additional information. However, the Wikipedia rules say secondary research -- reliably sourced. Timhowardriley (talk) 04:01, 1 May 2022 (UTC)

  WP:RS says secondary sources that present the same material are preferred.; primary sources are not prohibited. If you know of secondary or tertiary sources covering the same material, please add citations in addition to or in place of the current citations. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:12, 1 May 2022 (UTC)

  I don't mean to come across as fastidious. But just to be perfectly clear, secondary research is another way of saying not primary (original) research. (I wanted to word the sentence in the positive.) Of course, secondary research may be from primary sources or secondary sources. Timhowardriley (talk) 22:08, 2 May 2022 (UTC)

• Regarding "External events such as expiration of time slice, IPC signals and keyboard signals from the user do not fit the definition in Interrupt#Software interrupts": Quoting directly from the textbook: "Among the types of events that cause the kernel to generate a signal for a process are the following: 1) [omitted], 2) [omitted], 3) A software event occurred. For example, input became available on a file descriptor, the terminal window was resized, a timer went off, the process's CPU time limit was exceeded, or a child of this process terminated." The paragraph as written seems kosher. Timhowardriley (talk) 08:25, 1 May 2022 (UTC)

  Interrupt#Software interrupts reads A software interrupt is requested by the processor itself upon executing particular instructions or when certain conditions are met. Every software interrupt signal is associated with a particular interrupt handler.; that matches what I have seen elsewhere. The text you quoted does not claim that those events are software interrupts. That citation in no way justifies the existing text. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:12, 1 May 2022 (UTC)

  The sentence you quoted is uncited. The cited text I quoted does support the existing paragraph in the article. Timhowardriley (talk) 22:19, 2 May 2022 (UTC)

Notes

References

Software interrupt? (Third Opinion)

@Chatul: I'm thinking about posting this issue to Wikipedia:Third opinion. The instructions say, "[E]ditors are requested to present a short summary of the dispute, in plain English and preferably in a new subsection below the main discussion, so that 3O volunteers may find it easier to respond to." As I am the editor who wrote the article's existing operating system#Software interrupt section, I stand by my cited sentences. Please quote from the article the sentences that are being questioned. Also, present reliably sourced alternatives. Who knows, maybe this fresh start will alone resolve the conflict. Timhowardriley (talk) 22:54, 2 May 2022 (UTC)

Additional thought: The category of an event to be a hardware interrupt or a software interrupt may be divided on a thin line. For example, another textbook seems to categorize the context switch as a hardware interrupt. I put it in the software category because the cited textbook clearly put it here. So, if another textbook has an event categorized differently than the article's category, of course I will accommodate. Timhowardriley (talk) 23:36, 2 May 2022 (UTC)

The sentence in dispute is A software interrupt (also known as a signal) is a notification to a process that an event has occurred.. The dispute is on whether signals belong in the article and on whether, e.g., Supervisor Call instructions, overflow traps, belong in that section instead.

I took a look at the book you sited, and the relevant text does not say that a signal is an interrupt, but only that "Signals are sometimes described as software interrupts." The text in Interrupt#Software interrupts matches what I have seen, but I've added a {{cn}} template there.

There are machines with context-switch instructions, e.g., Move Stack on the B6500. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 13:23, 3 May 2022 (UTC)

1. Are you're saying the entire Software interrupt subsection should be removed from the Interrupt section because it doesn't contain the term Supervisor Call Instructions? Timhowardriley (talk) 15:13, 3 May 2022 (UTC)

   No, I'm initially saying that the text should be moved to an appropriate section because it has nothing to do with interrupts, any more than straw dummy has to do with either straw or dummies. I'm then saying that there is other information that is not present but belongs there, and giving SVC as an example. Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:30, 4 May 2022 (UTC)

2. Regarding "[Kerrisk] does not say that a signal is an interrupt, but only that 'Signals are sometimes described as software interrupts.'": Signal (IPC) is the UNIX jargon for software interrupt. Do you agree? Timhowardriley (talk) 22:03, 3 May 2022 (UTC)

   Of course I do not agree. Signal is the UNIX jargon for signal. Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:35, 4 May 2022 (UTC)

3. In Kerrisk's book, the sentence following the sentence you quoted is, "Signals are analogous to hardware interrupts in that they interrupt the normal flow of execution of a program[.]" The Interrupts section in this article says, "Interrupts cause the central processing unit (CPU) to have a control flow change away from the currently running process." Are you saying this is a contradiction? Timhowardriley (talk) 15:43, 3 May 2022 (UTC)

   Why would you imagine that I am saying that? What I am saying is that "foo is anlogous to bar" is not the same as "foo is bar". Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:38, 4 May 2022 (UTC)

4. Are you saying, because machines have context-switch instructions, the entire Software interrupt subsection should be removed from the Interrupt section? Timhowardriley (talk) 15:43, 3 May 2022 (UTC)

   No, I was simply commenting on your For example, another textbook seems to categorize the context switch as a hardware interrupt. and clarifying that a context switch could be part of the architecture rather than an OS construct, depending on the system under discussion. Shmuel (Seymour J.) Metz Username:Chatul (talk) 10:44, 4 May 2022 (UTC)

• In conclusion, you are claiming that the sentences in the Software interrupt subsection are bad sentences. However, you didn't present reliably sourced, alternative sentences. You didn't convey what good sentences should look like. Timhowardriley (talk) 11:25, 4 May 2022 (UTC)

  I'm saying

  1. There should be an IPC section, and information on signals belongs there, not under software interrupts
  2. The section on software interrupt should discuss the major types of synchronous interrupts, including
     1. Special instructions, e.g., INT, SVC, UUO
     2. Faults, e.g., addressing, invalid opcode, overflow
     3. Debugging and monitoring facilities, e.g., program-event recording (PER)

  Good sentences should say signal when they're describing signals. I'm still trying to find an online RS that is not behind a paywall. Meanwhile, I've created Wikipedia talk:WikiProject Computer science#Definition of software interrupt. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 15:35, 4 May 2022 (UTC)

I have reviewed Interrupt#Software_interrupts and it looks mostly good (I'm not sure interrupts from the MMU would be considered software interrupts). Operating_system#Software_interrupt, not so good. A signal is similar to a software interrupt or potentially initiated by a software interrupt but they are not the same. As explained in Interrupt#Software_interrupts, a software interrupt occurs when software executes an instruction that specifically requests it and, as a result, the CPU invokes an ISR – in the same way a hardware signal would invoke an ISR. ~Kvng (talk) 15:05, 8 May 2022 (UTC)

Regarding "not so good": You apparently agree with the INT machine instruction paragraph. What if it's the kernel executing INT? Are you questioning the error conditions? Are you questioning the user initiated termination? Are you questioning the UNIX kill() system call? Are you questioning the pipe coordinations? Are you questioning the normally occurring events -- timeslice/context switch or timer? I'm uneasy about the timeslice/context switch, but it's clearly in the textbook as a software interrupt. Timhowardriley (talk) 19:21, 8 May 2022 (UTC)

The only problem that I see with the INT paragraph is that it conflates machine language with assembly language.The second sentence should start with something like The assembler syntax is.

Depending on how you define kernel, an instruction like INT may be allowed or prohibited in the kernel. E.g., in OS/360, an SVC is allowed in a type 2, 3 or 4 SVC routine but not in a type 1 SVC routine.

I'm questioning 'everything that is not part of the computer's architecture. The material belongs in the article, but not in the Interrupts section.

There's more than one textbook, and other textbooks define software interrupt differently. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 00:06, 9 May 2022 (UTC)

@Timhowardriley, software interrupts use much of the same CPU hardware that hardware interrupts use so it is probably not right to say that a hardware interrupt is a message to the CPU and a software interrupt is not. Time-slice context switches are not software interrupts (though the do interrupt running software), they are a core operating system feature that is sometimes triggered by a hardware interrupt (timer). The interrupt character does interrupt a software process so it can be called a software interrupt but it is not what we're talking about here. ~Kvng (talk) 23:48, 11 May 2022 (UTC)

1. Regarding "so it is probably not right to say that a hardware interrupt is a message to the CPU and a software interrupt is not.": The sentences in the article you are referring to are paraphrases from two textbooks. I added the quotes from the textbooks in the citations with this edit. Do you agree with the paraphrasing? Timhowardriley (talk) 01:17, 12 May 2022 (UTC)
2. Regarding "Time-slice context switches are not software interrupts (though the do interrupt running software)": I used to also think so too. Then I discovered the alarm signal. In Unix-like OSs, SIGALRM sets the timer for when SIGPROF is sent to perform a context switch. Kerrisk writes on page 480, "ITIMER_PROF: Create a profiling timer. A profiling timer counts in process time (i.e., the sum of both user-mode and kernel-mode CPU time). When the timer expires, a SIGPROF signal is generated for the process." If you still don't agree that a time-slice is a software interrupt, then I'll move time-slices to outside of software interrupt. Timhowardriley (talk) 01:17, 12 May 2022 (UTC)

   Followup: I did a fresh look at Kerrisk's book, The Linux Programming Interface, and added the quote to the citation here. I'm now very convinced that time-slices are software interrupts. Timhowardriley (talk) 01:34, 12 May 2022 (UTC)

I added software ISR execution to the article and removed a sentence about messages. Does it read better, now? Timhowardriley (talk) 22:06, 8 May 2022 (UTC)

In all my research, a theme has formed: interrupts are signals -- signals either to the CPU or to a process. Even in the hardware context, Abraham Silberschatz writes in Operating System Concepts (1994), "Hardware may trigger an interrupt at any time by sending a signal to the CPU, usually by way of the system bus." Timhowardriley (talk) 22:06, 8 May 2022 (UTC)

That text is using signal in the generic English sense, not the term of art signal for Interprocess communication. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 00:06, 9 May 2022 (UTC)

@Kvng: Timhowardriley moved part of the discussion to #Does a signal cause a context switch?. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 11:27, 11 May 2022 (UTC)

RS for SYSENTER

There is a footnote mentioning SYSENTER that cites the URL https://wiki.osdev.org/SYSENTER, which looks like a good source for details; I have two concerns:

1. Does it satisfy RS?
2. Should it be changed from a raw URL to a full citation?

--Shmuel (Seymour J.) Metz Username:Chatul (talk) 12:23, 13 May 2022 (UTC)

1. Regarding its reliability: Yes. It says, "The SYSENTER/SYSEXIT instructions (and equivalent SYSCALL/SYSRET on AMD) enable fast entry to the kernel, avoiding interrupt overhead." This seems correct and is consistent with other material on SYSENTER. Timhowardriley (talk) 15:53, 13 May 2022 (UTC)

   That's the right answer to the wrong question. I'm not asking whether the footnote is correct and relevant, I'm asking whether the cited web pages is a reliable source as defined by Wikipedia in WP:RS, specifically, "Articles should be based on reliable, independent, published sources with a reputation for fact-checking and accuracy.". I have no idea what the reputation of that web site is, and I don't want to bother converting it to a full citation if somebody else is going to remove it as not RS. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 18:42, 13 May 2022 (UTC)

   Do you agree with the assertion that SYSENTER is an assembly instruction to avoid interrupt overhead? Or do you think it's a dubious assertion? Timhowardriley (talk) 03:54, 14 May 2022 (UTC)

2. Regarding should it be changed to a full citation? Sure. Timhowardriley (talk) 15:53, 13 May 2022 (UTC)

That's user generated content. It's not a reliable source. MrOllie (talk) 11:30, 16 May 2022 (UTC)

Does a signal cause a context switch?

[This thread was moved from above so it will be in its own section.] Timhowardriley (talk) 10:12, 10 May 2022 (UTC)

Followup: Do you agree that a signal causes a change from the currently running process? Timhowardriley (talk) 19:28, 8 May 2022 (UTC)

That depends on what you mean by signal. An interrupt need not cause a context switch. An IPC signal need not cause a context switch. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 00:06, 9 May 2022 (UTC)

Okay, this is the root of the problem. I have yet see in text that an interrupt may occur without a context switch. Also, I have yet to see in text that an IPC signal may occur without a context switch. Timhowardriley (talk) 17:26, 9 May 2022 (UTC)

The citation that you gave does not the reference to a context switch.

An SVC interrupt in, e.g., OS/360, MVS, does not in general change the context. A SIGILL signal does not switch processes. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:04, 9 May 2022 (UTC)

I respectfully disagree. Tannenbaum clearly says on page 308, "Like the trap, the interrupt stops the running program and transfers control to an interrupt handler[.]" This is a context switch. I can't comment about the SVC interrupt because I have no reliable text to reference. However, I do know that OS/360 is retired. I will believe SIGKILL does a context switch until I see text saying it doesn't. Timhowardriley (talk) 03:09, 10 May 2022 (UTC)

Whoops! I read "SIGKILL" when you wrote "SIGILL". SIGILL is the malformed (illegal) machine instruction signal. It is intuitively correct to assume that a process with an illegal instruction will be switched out and aborted. Timhowardriley (talk) 10:12, 10 May 2022 (UTC)

Regarding a Supervisor Call (SVC) interrupt in MVS: Like my lack of comment on OS/360, I have no reliable source to reference. However, the burden is upon you to provide the reliable source for your assertions. If you have a reliable source that talks about MVS servicing an interrupt without peforming a context switch, then the article will benefit from your edits. Timhowardriley (talk) 10:12, 10 May 2022 (UTC)

Generally speaking, interrupts (AKA signals) consume many CPU cycles. Moreover, advancements in hardware have made what used to be an interrupt to no longer need to perform a context switch. For example, new processors support the SYSENTER assembly instruction. See https://wiki.osdev.org/SYSENTER . However, I surmise that SYSENTER is executed for only a subset of system calls. For example, getting the process ID of a parent process is a system call that currently performs an unnecessary context switch. For a parent process ID request, I surmise that system programmers are working to take advantage of SYSENTER and skip the context switch. Anyway, if you come across a reliable source describing SYSENTER, then the article would benefit from your edits. Timhowardriley (talk) 10:12, 10 May 2022 (UTC)

The first step should be splitting the text into separate sections for generic text and text specific to particular operating systems. As part of that, I would include references for a lot more than just interrupt handling. Also, if you really want me to provide sources then stop removing the sources that I have provided. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 12:52, 10 May 2022 (UTC)

Regarding your references: What claim are you sourcing? What page supports your claim? Timhowardriley (talk) 16:11, 10 May 2022 (UTC)

Regarding "stop removing the sources that I have provided": What edits are you referring to? Timhowardriley (talk) 16:11, 10 May 2022 (UTC)

Regarding "MVS, does not in general change the context": Is it because of this claim that you reverted my edit here? As requested above, please support this claim with a reliable source, including the page number. Timhowardriley (talk) 16:18, 10 May 2022 (UTC)

The Wikipedia article context switch says, "A context switch can also occur as the result of an interrupt[.]" Timhowardriley (talk) 20:03, 10 May 2022 (UTC)

The key word is can; it doers not say that an interrupt always causes a context switch. In fact, the same articles also says When the system transitions between user mode and kernel mode, a context switch is not necessary; a mode transition is not by itself a context switch.. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 23:32, 10 May 2022 (UTC)

@Chatul:: So you agree that an interrupt can/may/might/willsometimes cause a context switch. Right? Timhowardriley (talk) 06:38, 12 May 2022 (UTC)

More precisely, I agree that an interrupt service routine can cause a context switch in at least three cases:

1. The kernel runs in a special context
2. The ISR imposes a delay on the current thread or process, e.g., a P operation on a busy semaphore.
3. The ISR makes a higher priority thread/process eligible to run

I don't agree that the interrupt itself causes a context switch. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 09:48, 12 May 2022 (UTC)

As Chatul says, an IPC signal doesn't necessarily cause a context switch. It depends on how they're implemented. IIRC when a process sends a signal to itself via the raise() call it is unlikely there will be a context switch, for example. MrOllie (talk) 11:39, 16 May 2022 (UTC)

@Timhowardriley: I added a {{disputed}} tag, which User:Timhowardriley removed with the claim "Reverted edit b/c the tagged sentence correctly paraphrases the source text. The next sentence references context switch.". Actually, the next sentence does not mention context, but only state, e.g., registers. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 12:43, 11 May 2022 (UTC)

Your first tag bomb was a swing and a miss. Both authors are referring to context switches for interrupts. Please stop your disruptive editing. Timhowardriley (talk) 18:27, 11 May 2022 (UTC)

This is what you call civil discourse? You are the one engaging ion disruptive editing. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 09:48, 12 May 2022 (UTC)

References

Unethically misquoting a textbook

@Chatul: Abraham Silberschatz's textbook Operating System Concepts (1994) was misquoted with this edit. The Wikipedia editor moved a sentence from the article into page 105 of the textbook. Page 105 does not say, "An interrupt service routine may cause the central processing unit (CPU) to have a context switch." This is highly unethical. Please move the sentence from the citation quote back to the article. Timhowardriley (talk) 13:39, 13 May 2022 (UTC)

Please stop the insane accusations and enter into a civil discussion. I did nothing unethical, nor did I misquote anything. Unlike you, I'm not perfect, and failed to notice that the references belonged the middle of the sentence rather than the end --Shmuel (Seymour J.) Metz Username:Chatul (talk) 18:48, 13 May 2022 (UTC)

I'm sorry to have categorized your edit as unethical, if you are unaware of the result. Before your edit, Operating Systems Concepts (page 105) said, "Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. This task is known as a context switch." After your edit, the article erroneously claims page 105 says, "Switching the CPU to another process requires saving the state of the old process and loading the saved state for the new process. An interrupt service routine may cause the central processing unit (CPU) to have a context switch." Please fix this. Timhowardriley (talk) 21:03, 13 May 2022 (UTC)

Please check my latest edit to verify that I correctly disentangled inline text from text quoted in the citation. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 17:48, 30 May 2022 (UTC)

Removal of IBSYS/IBJOB

@Maury Markowitz: An edit by Maury Markowitz on June 17 removed mention of IBM's IBSYS/IBJOB. I believe that, due to their influence on GECOS and OS/360, IBSYS/IBJOB and the related PR155 were important milestones and should be mentioned. --Shmuel (Seymour J.) Metz Username:Chatul (talk) 21:16, 17 June 2022 (UTC)

I don't recall doing this, it must have been a fat finger. Maury Markowitz (talk) 21:47, 17 June 2022 (UTC)

References

RS for influence of IBSYS/IBJOB on GCOS (née GECOS)?

Does anybody have a WP:RS for the influence of IBM IBSYS/IBJOB on GECOS? Shmuel (Seymour J.) Metz Username:Chatul (talk) 16:32, 18 December 2022 (UTC)

"Commodity operating systems" listed at Redirects for discussion

An editor has identified a potential problem with the redirect Commodity operating systems and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2023 January 24 § Commodity operating systems until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Steel1943 (talk) 16:36, 24 January 2023 (UTC)

Edit request 11

Please remove the unsourced "modes" section and replace the first paragraph of the "Kernel" section with the following text, which also covers modes:

Extended content

The kernel is the part of the operating system that provides protection between different applications and users. This protection is key to improving reliability by keeping errors isolated to one program, as well as security by limiting the power of malicious software and protecting private data, and ensuring that one program cannot monopolize the computer's resources. Most operating systems have two modes of operation: in user mode, the hardware checks that the software is only executing legal instructions, whereas the kernel has unrestricted powers and is not subject to these checks. The kernel also manages memory for other processes and controls access to input/output devices. References

Thanks Buidhe paid (talk) 07:09, 14 February 2024 (UTC)

I believe that it would be better to add sources to the existing text: some processors have more than two modes. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 14:00, 14 February 2024 (UTC)

I updated the text to mention that some OS have a different number of modes. However, according to Tanenbaum, most OS have two modes, so going into detail on other mode systems is likely UNDUE. The current text of the modes section is excessive detail for this article compared to the coverage of user/kernel/other modes in OS textbooks (just a couple paragraphs out of hundreds or 1000+ pages in those I consulted). Buidhe paid (talk) 04:51, 15 February 2024 (UTC)

Edit request 1

Please replace the current contents of the "security" subsection with the following:

Extended content

Security means protecting users from other users of the same computer, as well as from those who seeking remote access to it over a network. Operating systems security rests on achieving the CIA triad: confidentiality (unauthorized users cannot access data), integrity (unauthorized users cannot modify data), and availability (ensuring that the system remains available to authorized users, even in the event of a denial of service attack). As with other computer systems, isolating security domains—in the case of operating systems, the kernel, processes, and virtual machines—is key to achieving security. Other ways to increase security include simplicity to minimize the attack surface, locking access to resources by default, checking all requests for authorization, principle of least authority (granting the minimum privilege essential for performing a task), privilege separation, and reducing shared data. Some operating system designs are more secure than others. Those with no isolation between the kernel and applications are least secure, while those with a monolithic kernel like most general-purpose operating systems are still vulnerable if any part of the kernel is compromised. A more secure design features microkernels that separate the kernel's privileges into many separate security domains and reduce the consequences of a single kernel breach. Unikernels are another approach that improves security by minimizing the kernel and separating out other operating systems functionality by application. Most operating systems are written in C or C++, which can cause vulnerabilities. Despite various attempts to protect against them, a substantial number of vulnerabilities are caused by buffer overflow attacks, which are enabled by the lack of bounds checking. Hardware vulnerabilities, some of them caused by CPU optimizations, can also be used to compromise the operating system. Programmers coding the operating system may have deliberately implanted vulnerabilities, such as back doors. Operating systems security is hampered by their increasing complexity and the resulting inevitability of bugs. Because formal verification of operating systems may not be feasible, operating systems developers use hardening to reduce vulnerabilities, such as address space layout randomization, control-flow integrity, access restrictions, and other techniques. Anyone can contribute code to open source operating systems, which have transparent code histories and distributed governance structures. Their developers work together to find and eliminate security vulnerabilities, using techniques such as code review and type checking to avoid malicious code. Andrew S. Tanenbaum advises releasing the source code of all operating systems, arguing that it prevents the developer from falsely believing it is secret and relying on security by obscurity. References

Please add the following references to the "further reading" section:

• Berntsson, Petter Sainio; Strandén, Lars; Warg, Fredrik (2017). Evaluation of Open Source Operating Systems for Safety-Critical Applications. Springer International Publishing. pp. 117–132. ISBN 978-3-319-65948-0.
• Richet, Jean-Loup; Bouaynaya, Wafa (2023). "Understanding and Managing Complex Software Vulnerabilities: An Empirical Analysis of Open-Source Operating Systems". Systèmes d'information & management. 28 (1): 87–114. doi:10.54695/sim.28.1.0087.

Reasons: add refs, rewrite according to due weight in reliable sources, cover security concerns of open source operating systems

Thank you Buidhe paid (talk) 03:58, 2 February 2024 (UTC)

@Buidhe paid, these are a lot of changes. I admit I haven't reviewed it in detail, but at a glance it looks fine. Why exactly are you submitting a COI edit request? I understand you've declared a COI with regards to Anderson & Dahlin but you are not adding or removing any references to that book. I feel like you should just make this change directly to the article. Mokadoshi (talk) 08:59, 9 April 2024 (UTC)

ok, I will do that. Technically I have a COI because I received pay for these edits, but I am only asked to improve articles according to existing policy /guidelines. Buidhe paid (talk) 21:46, 9 April 2024 (UTC)

Definition and purpose

An operating system is difficult to define, but has been called "the layer of software that manages a computer's resources for its users and their applications". Operating systems include the software that is always running, called a kernel—but can include other software as well. The two other types of programs that can run on a computer are system programs—which are associated with the operating system, but may not be part of the kernel—and applications—all other software.

There are three main purposes that an operating system fulfills:

• Operating systems allocate resources between different applications, deciding when they will receive central processing unit (CPU) time or space in memory. On modern personal computers, users often want to run several applications at once. In order to ensure that one program cannot monopolize the computer's limited hardware resources, the operating system gives each application a share of the resource, either in time (CPU) or space (memory). The operating system also must isolate applications from each other to protect them from errors and security vulnerability is another application's code, but enable communications between different applications.
• Operating systems provide an interface that abstracts the details of accessing hardware details (like physical memory) to make things easier for programmers. Virtualization also enables the operating system to mask limited hardware resources; for example, virtual memory can provide a program with the illusion of nearly unlimited memory that exceeds the computer's actual memory.
• Operating systems provide common services, such as an interface for accessing network and disk devices. This enables an application to be run on different hardware without needing to be rewritten. Which services to include in an operating system varies greatly, and this functionality makes up the great majority of code for most operating systems.

References

|}

• Tanenbaum, Andrew S.; Bos, Herbert (2023). Modern Operating Systems, Global Edition. Pearson Higher Ed. ISBN 978-1-292-72789-9.

Reason: all OS textbooks that I was able to access started out by defining what an OS is and explaining its purpose. This section is missing in the current article. Buidhe paid (talk) 20:52, 2 February 2024 (UTC)

@Buidhe paid: Historically the term operating system has included a lot more than kernels, typically including unprivileged program such as commands, compilers and binders.

Also, the unpaide {{collapse bottom}} generates an extraneous }} line after the references. My reading of the documentation suggests that it wouldn't be appropriate even if properly paired with a {{collapse top}}. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 22:30, 2 February 2024 (UTC)

If you can improve on my text, please feel free to do so. I am just reporting what it says in the cited source. I cannot see any stray curly braces and if there were any, I assume the person implementing the request would disregard them. Yes, you need a collapse bottom to mark the end of the collapsed section, otherwise your comment would be collapsed too. Buidhe paid (talk) 22:46, 2 February 2024 (UTC)

Note: I checked a few more sources and tweaked the definition accordingly. Buidhe paid (talk) 00:05, 6 February 2024 (UTC)

 Done Subwayfares (talk) 13:50, 23 May 2024 (UTC)

Edit request 4

Please change the section header titled "multitasking" to "concurrency". Reason: this is a more commonly used term in OS textbooks (see here for evidence).

Also, please change the content of the section (including the hatnote) to:

Extended content

Concurrency See also: Computer multitasking and Process management (computing) Concurrency refers to the operating system's ability to carry out multiple tasks simultaneously. Virtually all modern operating systems support concurrency. Threads enable splitting a process' work into multiple parts that can run simultaneously. The number of threads is not limited by the number of processors available. If there are more threads than processors, the operating system kernel schedules, suspends, and resumes threads, controlling when each thread runs and how much CPU time it receives. During a context switch a running thread is suspended, its state is saved into the thread control block and stack, and the state of the new thread is loaded in. Historically, on many systems a thread could run until it relinquished control (cooperative multitasking). Because this model can allow a single thread to monopolize the processor, most operating systems now can interrupt a thread (preemptive multitasking). Threads have their own thread ID, program counter (PC), a register set, and a stack, but share code, heap data, and other resources with other threads of the same process. Thus, there is less overhead to create a thread than a new process. On single-CPU systems, concurrency is switching between processes. Many computers have multiple CPUs. Parallelism with multiple threads running on different CPUs can speed up a program, depending on how much of it can be executed concurrently. Synchronization Main article: Synchronization (computer science) Given that threads usually share data with other threads from the same process, the order in which threads are executed could impact the result. There are no guarantees about the order of execution between different threads. This makes debugging multithreaded processes much more difficult. If a program produces a different result depending on the order in which threads are executed, this is called a race condition. There are different ways of avoiding race conditions. A simple option is atomic operations that cannot be interrupted or interleaved with other processes. Shared objects (sometimes called monitors) encapsulating heap-allocated memory into an object. The synchronization status is built into the object and hidden from the programmer, but enables the object to be locked while in use by another thread. Condition variables enable a thread to wait until a lock has been released. Locks can only be used by one thread at a time, often reducing performance. In an attempt to increase parallelism and improve performance, programmers can split a shared object into multiple shared objects. However, this approach can cause unexpected results from interactions across objects. The use of multiple locks can cause a deadlock where multiple threads are waiting for each other to finish and release their lock on a resource, thus halting execution. Many operating systems include deadlock detection and recovery features, for example, killing processes, interrupting a process, taking advantage of checkpoints to move back in the execution of a program. Although the operating system can almost never prevent deadlocks, some use heuristics similar to the banker's algorithm to avoid some cases. Communication deadlocks occur when two processes are waiting for a reply from each other. Timeouts are often employed to break these deadlocks. References

Reason: fix unsourced text and ensure that topics are covered according to their prominence in reliable sources (please see the summary of several OS textbooks on my sandbox talk page).

Thank you Buidhe paid (talk) 19:30, 3 February 2024 (UTC)

I have a few copy-editing comments, suggestions, and questions before I implement this one. I'm not a subject matter expert, so I want to be very sure that I'm not unintentionally making the information less accurate with these suggestions.

Extended content

Original: Threads have their own thread ID, program counter (PC), a register set, and a stack, but share code, heap data, and other resources with other threads of the same process. Suggested: Threads have their own thread ID, program counter (PC), register set, and stack, but share code, heap data, and other resources with other threads of the same process. Reasoning: maintain grammatical structure throughout list Original: Shared objects (sometimes called monitors)[18] encapsulating heap-allocated memory into an object. Comment: Is there a word missing or something in this sentence? I can't parse it. Original: Many operating systems include deadlock detection and recovery features, for example, killing processes, interrupting a process, taking advantage of checkpoints to move back in the execution of a program. Suggested: Many operating systems include deadlock detection and recovery features. These include killing processes, interrupting processes, and taking advantage of checkpoints to move back in the execution of a program. Reasoning: I think this is a little bit clearer if you break it up into two sentences; I also changed the wording a little to maintain parallel grammatical structure throughout the list

Let me know what you think. I'm happy to make changes as I implement the edit, or (maybe easier haha) you can adjust the original text for me to copy and paste. Subwayfares (talk) 14:24, 23 May 2024 (UTC)

Thank you for helping with these edits.

1. This is an improvement, thanks
2. Change encapsulating to encapsulate good catch
3. Good fix

Buidhe paid (talk) 14:49, 23 May 2024 (UTC)

One last question as I start to put this together - In the deadlocks section, the sentence "The most common kind is a resource deadlock where multiple processes request the same resource that only one can have at a time." is commented out. Is there a reason not to include it in the article? Subwayfares (talk) 15:11, 23 May 2024 (UTC)

The obvious reason is that it's not true. A deadlock involves more than a single resource. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 15:54, 23 May 2024 (UTC)

Correct, it is one process holding resource 1 while requesting resource 2 while another has 2 and needs 1 (for example) Buidhe paid (talk) 19:10, 23 May 2024 (UTC)

 Partly done @Buidhe paid: I added your concurrency content and section, but kept and indented the multitasking section, since it's a form of concurrency. See [[1]]. STEMinfo (talk) 23:12, 24 May 2024 (UTC)

Yes, "multitasking" is a word used for concurrency as it relates to multiple processes run by the OS on a single cpu, but I don't see why we need a new section about that when it is already most of the content covered under concurrency. Regardless of that, the older "multitasking" content is entirely unsourced, partly duplicates the content I added and has some undue details. Buidhe paid (talk) 00:10, 26 May 2024 (UTC)

Note that the nomenclature is not consistent; depending on the text, multitasking may refer to concurrent threads within a single application or to multiple applications running concurrently. Some of the same synchronization issues apply to both. — Preceding unsigned comment added by Chatul (talk • contribs) 01:53, 26 May 2024 (UTC)

Edit request 2

Please remove the top-level section on "real-time operating systems" (they will be covered under "types of operating systems") and change the content of the "Types of operating systems" section to the following:

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Multicomputer operating systems With multiprocessors multiple CPUs share memory. A multicomputer or cluster computer has multiple CPUs, each of which has its own memory. Multicomputers were developed because large multiprocessors are difficult to engineer and prohibitively expensive; they are universal in cloud computing because of the size of the machine needed. The different CPUs often need to send and receive messages to each other; to ensure good performance, the operating systems for these machines need to minimize this copying of packets. Newer systems are often multiqueue—separating groups of users into separate queues—to reduce the need for packet copying and support more concurrent users. Another technique is remote direct memory access, which enables each CPU to access memory belonging to other CPUs. Multicomputer operating systems often support remote procedure calls where a CPU can call a procedure on another CPU, or distributed shared memory, in which the operating system uses virtualization to generate shared memory that does not actually exist. Distributed systems A distributed system is a group of distinct, networked computers—each of which might have their own operating system and file system. Unlike multicomputers, they may be dispersed anywhere in the world. Middleware, an additional software layer between the operating system and applications, is often used to improve consistency. Although it functions similarly to an operating system, it is not a true operating system. Embedded Embedded operating systems are designed to be used in embedded computer systems, whether they are internet of things objects or not connected to a network. Embedded systems include many household appliances. The distinguishing factor is that they do not load user-installed software. Consequently, they do not need protection between different applications, enabling simpler designs. Very small operating systems might run in less than 10 kilobytes, and the smallest are for smart cards. Examples include Embedded Linux, QNX, VxWorks, and the extra-small systems RIOT and TinyOS. Real-time A real-time operating system is an operating system that guarantees to process events or data by or at a specific moment in time. Hard real-time systems require exact timing and are common in manufacturing, avionics, military, and other similar uses. With soft real-time systems, the occasional missed event is acceptable; this category often includes audio or multimedia systems, as well as smartphones. In order for hard real-time systems be sufficiently exact in their timing, often they are just a library with no protection between applications, such as eCos. Virtual machine A virtual machine is an operating system that runs as an application on top of another operating system. The virtual machine is unaware that it is an application and operates as if it had its own hardware. Virtual machines can be paused, saved, and resumed, making them useful for operating systems research, development, and debugging. They also enhance portability by enabling applications to be run on a computer even if they are not compatible with the base operating system. References

Also, please add the following source to further reading:

• Silberschatz, Abraham; Galvin, Peter B.; Gagne, Greg (2018). Operating System Concepts (10 ed.). Wiley. ISBN 978-1-119-32091-3.

Reason: fix unsourced text, add a concise summary of virtual machines. I removed the "Single- and multi-user" section because it duplicates information that is in the new "Concurrency" section. Buidhe paid (talk) 02:57, 10 February 2024 (UTC)

• Done by Subwayfares, thanks! Buidhe paid (talk) 02:43, 23 May 2024 (UTC)

  I might come back and look at the others, but my editing is pretty sporadic, so I can't make promises. ;) Thanks for the contributions & for formatting them clearly. Subwayfares (talk) 02:51, 23 May 2024 (UTC)

"Virtual machine" doesn't usually refer to an operating system. A system virtual machine is implemented by a hypervisor and whatever assistance is provided by the underlying platform on which the hypervisor runs; the hypervisor could be viewed as an operating system, the "applications" that run onto of which are themselves operating systems. (There are also process virtual machines, such as a Java virtual machine, but the software providing that virtual machine is generally not thought of as being like an operating system.) Guy Harris (talk) 07:47, 26 May 2024 (UTC)

Edit request 5

Please replace the current "Disk access and file systems" and "Disk drivers" sections with the following text under the heading "File system":

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Main article: File system See also: Virtual file system File systems allow users and programs to organize and sort files on a computer, often through the use of directories (or folders). Permanent storage devices used in twenty-first century computers, unlike volatile dynamic random-access memory (DRAM), are still accessible after a crash or power failure. Permanent (non-volatile) storage is much cheaper per byte, but takes several orders of magnitude longer to access, read, and write. The two main technologies are a hard drive consisting of magnetic disks, and flash memory (a solid state drive that stores data in electrical circuits). The latter is more expensive but faster and more durable. File systems are an abstraction used by the operating system to simplify access to permanent storage. They provide human-readable filenames and other metadata, increase performance via amortization of accesses, prevent multiple threads from accessing the same section of memory, and include checksums to identify corruption. File systems are composed of files (named collections of data, of an arbitrary size) and directories (also called folders) that list human-readable filenames and other directories. An absolute file path begins at the root directory and lists subdirectories divided by punctuation, while a relative path defines the location of a file from a directory. System calls (which are sometimes wrapped by libraries) enable applications to create, delete, open, and close files, as well as link, read, and write to them. All these operations are carried out by the operating system on behalf of the application. The operating system's efforts to reduce latency include storing recently requested blocks of memory in a cache and prefetching data that the application has not asked for, but might need next. Device drivers are software specific to each input/output (I/O) device that enables the operating system to work without modification over different hardware. Another component of file systems is a dictionary that maps a file's name and metadata to the data block where its contents are stored. Most file systems use directories to convert file names to file numbers. To find the block number, the operating system uses an index (often implemented as a tree). Separately, there is a free space map to track free blocks, commonly implemented as a bitmap. Although any free block can be used to store a new file, many operating systems try to group together files in the same directory to maximize performance, or periodically reorganize files to reduce fragmentation. Maintaining data reliability in the face of a computer crash or hardware failure is another concern. File writing protocols are designed with atomic operations so as not to leave permanent storage in a partially written, inconsistent state in the event of a crash at any point during writing. Data corruption is addressed by redundant storage (for example, RAID—redundant array of inexpensive disks) and checksums to detect when data has been corrupted. With multiple layers of checksums and backups of a file, a system can recover from multiple hardware failures. Background processes are often used to detect and recover from data corruption. References

Reason: add sources, improve high-level explanation, harmonize coverage proprortionate to reliable sources. Giving disk drivers a separate section seems UNDUE given that they are only a couple paragraphs in some of the text books (A&D, Silberschatz et al.) and given no more than two pages (in Tanenbaum). Buidhe paid (talk) 00:41, 4 February 2024 (UTC)

 Done Subwayfares (talk) 15:58, 23 May 2024 (UTC)

The mention of system calls sometimes being wrapped by libraries is not specific to those system calls that perform file system operations. System calls are mentioned in several paragraphs, and all of those may be wrapped by libraries. (In operating systems where the APIs are defined as higher-level-language procedure calls, they're typically wrapped by some library call, even if the wrapper is a small assembly-language wrapper around the instruction that performs the system call.) Guy Harris (talk) 08:15, 26 May 2024 (UTC)

Edit request 10

Please replace the current sections "Examples" and "Market share" with one section called "Popular operating systems", with the following content:

Extended content

Further information: Usage share of operating systems and Comparison of operating systems In the personal computer market, as of September 2023, Microsoft Windows has the highest market share, around 68%. macOS by Apple Inc. is in second place (20%), and the varieties of Linux, including ChromeOS, are collectively in third place (7%). In the mobile sector (including smartphones and tablets), as of September 2023, Android's share is 68.92%, followed by Apple's iOS and iPadOS with 30.42%, and other operating systems with .66%. Linux Main article: Linux Layers of a Linux system Linux is a free software distributed under the GNU General Public License (GPL), which means that all of its derivatives are legally required to release their source code. Linux was designed by programmers for their own use, thus emphasizing simplicity and consistency, with a small number of basic elements that can be combined in nearly unlimited ways, and avoiding redundancy. Its design is similar to other UNIX systems not using a microkernel. It is written in C and uses UNIX System V syntax, but also supports BSD syntax. Linux supports standard UNIX networking features, as well as the full suite of UNIX tools, while supporting multiple users and employing preemptive multitasking. Initially of a minimalist design, Linux is a flexible system that can work in under 16 MB of RAM, but still is used on large multiprocessor systems. Similar to other UNIX systems, Linux distributions are composed of a kernel, system libraries, and system utilities. Linux has a graphical user interface (GUI) with a desktop, folder and file icons, as well as the option to access the operating system via a command line. Android is a partially open-source operating system closely based on Linux and has become the most widely used operating system by users, due to its popularity on smartphones and, to a lesser extent, embedded systems needing a GUI, such as "smart watches, automotive dashboards, airplane seatbacks, medical devices, and home appliances". Unlike Linux, much of Android is written in Java and uses object-oriented design. Microsoft Windows Main article: Microsoft Windows Security descriptor for a file that is read-only by default, specified no access for Elvis, read/write access for Cathy, and full access for Ida, the owner of the file Windows is a proprietary operating system that is widely used on desktop computers, laptops, tablets, phones, workstations, enterprise servers, and Xbox consoles. The operating system was designed for "security, reliability, compatibility, high performance, extensibility, portability, and international support"—later on, energy efficiency and support for dynamic devices also became priorities. Windows Executive works via kernel-mode objects for important data structures like processes, threads, and sections (memory objects, for example files). The operating system supports demand paging of virtual memory, which speeds up I/O for many applications. I/O device drivers use the Windows Driver Model. The NTFS file system has a master table and each file is represented as an record with metadata. The scheduling includes preemptive multitasking. Windows has many security features; especially important are the use of access-control lists and integrity levels. Every process has an authentication token and each object is given a security descriptor. Later releases have added even more security features. References

Reason: The only two OS textbooks with case studies have Linux and Windows, so if we're going to include a section with specific examples, that's probably the ones that should be there. This is a top level article and information about specific operating systems likely belongs in their own article or other subarticles such as comparison of operating systems. My version improves summary style and also fixes unsourced content issues. Buidhe paid (talk) 04:00, 7 February 2024 (UTC)

Or usage share of operating systems, which is a page that directly covers market share. Guy Harris (talk) 17:05, 26 May 2024 (UTC)