Talk:Disk operating system

DOS component separate in early days of computing?

The article now says "In the early days of computing, hard drive space was often limited, so the disk operating system was an extension of the operating system. This component was only loaded if it was needed. Otherwise, disk-access would be limited to low-level operations such as reading and writing disks at the sector-level." Is that referring to the "early days of computing" in the sense of the 1950's and early-to-mid 1960's, or to the "early days of computing" in the sense of the early days of microcomputing? DOS/360 was a full OS, not an extension to a base OS, loaded only when needed. Guy Harris 20:50, 21 January 2006 (UTC)

This refers to the early days of microcomputing (home computers). I have changed computing to microcomputing in the paragraph you quoted. I have also made more of a distinction between operating-system components called "disk operating systems" and operating systems called "Disk Operating System" (eg. DOS/360). Ae-a 15:45, 25 January 2006 (UTC)

Dave's Operating System

Moved from article page Redrose64 (talk) 20:37, 2 January 2012 (UTC)

My understanding of DOS is that it originally meant "Dave's Operating System". Dave was a realator in San Francisco who played with computers as a hobby. When Bill Gates signed the deal with IBM for an operating system, he did not have one. He was however aware of Dave's system. Unlike Gate's licensing deal with IBM, Gate bought the operating system for $25,000 from Dave. The system was really in the infant stages but it immedialely gave Microsoft a platform to develop "DOS, Disk Operating System.

I obtained this information first from a PBS TV program and since have talked with several former IBM employees who confirmed the story. I would say that it still needs further investigation for accuracy, however if true is a fascinating insight on how Microsoft started. Capn BJ —Preceding unsigned comment added by 166.248.73.119 (talk) 16:47, 31 December 2011‎

I'm afraid, you are mixing up a few things here. You are talking about Microsoft and MS-DOS, however, the term "DOS" for Disk Operating System long pre-dates the advent of MS-DOS, and was used by many operating systems completely unrelated to MS-DOS at the time (and that's what this article is about). Also, the operating system offered by Microsoft as MS-DOS (and by IBM as PC DOS) had its origins in 86-DOS, an operating system developed by Tim Paterson of Seattle Computer Products (SCP) as a rudimentary clone of Digital Research's CP/M (aka CP/M-80), but ported to run on 8080/8086 processors (and with two significant differences: a different disk buffer mechanism and the introduction of the FAT12 filesystem), whereas Digital Research's CP/M itself was only available for 8080/Z80 processors. CP/M-86 for 8086/8088 processors was not available when 86-DOS development started in 1979 (still called QDOS at this time), but it was available in 1981 at about the same time as IBM began shipping the IBM PC. If you are interested in the early history of MS-DOS, please make yourself familiar with 86-DOS. --Matthiaspaul (talk) 21:30, 2 January 2012 (UTC)

How does a Disk Operating System differ from an Operating System?

From the description it's not clear.

... refer to an operating system software used in most computers that provides the abstraction and management of secondary storage devices and the information on them (e.g., file systems for organizing files of all sorts). Such software is referred to as a disk operating system when the storage devices it manages are made of rotating platters, such as floppy disks or hard disks.

Abstracting and management of storage is something that all Operating Systems do.

173.13.156.125 (talk) 18:44, 10 May 2015 (UTC)

Well, the difference is whether "the storage devices it manages are made of rotating platters, such as floppy disks or hard disks" - but that makes a lot of operating systems not listed here "disk operating systems". The criterion for listing in "Disk operating systems that were extensions to the OS" and "Disk operating systems that were the main OS" appears to be "do they have either "DOS" or "Disk" in their names", which is bogus, because there are and were a lot of operating systems where "the storage devices [they manage] are made of rotating platters, such as floppy disks or hard disks" that aren't listed here (and because, for example, the operating system on the machine on which I'm typing this started out managing rotating-platter storage devices, but the main storage on the machine on which I'm typing this is flash storage). Guy Harris (talk) 19:57, 13 August 2018 (UTC)

Heck, for that matter, IBM had DOS/360 and OS/360 as (near-)contemporary OSes for System/360 ("near-" because DOS/360 came out before OS/360 finally shipped, but once OS/360 shipped, they were both offered, with DOS/360 being for lower-end machines that couldn't run OS/360 or couldn't run it well). Both were operating systems that can manage storage devices made of rotating platters and, I think, both were operating systems that required rotating-platter storage. (TOS/360 was an OS that supported using just tapes; it may have been "DOS/360 without the disk support". I don't think it lasted very long.)

So the concept of a "disk operating system" is spectacularly ill-defined, so I'm not sure why it deserves a Wikipedia page. A more narrowly-defined concept might deserve a page, e.g. the concept of an operating system from the early microcomputer days, for some appropriately-defined value of "early", that supports disk file systems might deserve a page. I'm not sure whether 1981 would be too late for an appropriate definition of "early", thus ruling out DOS as a Disk Operating System; I'd require that "early" refer to an era in which there were significant operating systems that didn't use disks, e.g. cassette-tape-based OSes. Guy Harris (talk) 07:05, 20 November 2018 (UTC)

I'd say that disk operating system does deserve a page. I agree that it's ill defined. but... so are many other terms. Consider: what is an operating system? What is a shell? we have to take a stab at describing them even if it's hard to do; even if the terms are wishy washy. Stevebroshar (talk) 18:42, 16 May 2025 (UTC)

Good question. IMO a disk operating system is a small version of a full operating system. In a modern system there is an OS and there is a file system. They might be intertwined or rather separate. But the operating system and the file system are relatively sophisticated and at least somewhat separate from each other. A DOS is like a very simple OS that only works with disk storage. the distraction between OS and DOS is not super clear. It includes complexity and it's historical. No one uses DOS for modern computers... partially since technology is different and partially due to shifts in language that tend to happen over long periods of time. Stevebroshar (talk) 18:54, 16 May 2025 (UTC)

IMO a disk operating system is a small version of a full operating system. So what parts get removed from a full OS to make it a DOS?

In a modern system there is an OS and there is a file system. They might be intertwined or rather separate. Most modern operating systems include support for multiple types of file system, some implemented on the modern version of what IBM called DASDs (that modern version being floppy disk drives, HDDs, and flash drives/memory cards/SSDs), on read-only or read-mostly media such as CD-ROMs and DVD-ROMs, on networks (NFS, SMB, AFP, etc.), and so forth. There may also be third-party file systems that can run on them.

But the operating system and the file system are relatively sophisticated and at least somewhat separate from each other. "Separate" in that the file systems can be thought of as "plugins" (even if they're "built-in" plugins rather than, say, loadable kernel modules).

A DOS is like a very simple OS that only works with disk storage. In System/360, DOS/360 was simpler than OS/360, but I'm not sure it was "very simple" for that era; some historical context is at DOS/360 and successors § History. DOS/360 also worked with tape drives. Microcomputer OSes with "DOS" in the name may have been simple, but that's because microcomputer OSes were generally simple in that era; it has nothing to do with the "D" in "DOS". Guy Harris (talk) 19:35, 16 May 2025 (UTC)

You make curios inferences. One need not remove to have a small version of something. It can be inherently small compared to something else. In particular, older OSes (such as DOSes), are smaller and less complicated than modern OSes; not saying they were not complex for the time. They are simple compared to modern. I am comparing older tech with newer. And that seems appropriate for DOS since IMO it's a historical term. It was popular for a period is time but no longer is popular; is not used and does not apply to a modern OS. ... WRT separation of OS from file system, DOS refers to an age gone by when there was less separation than today. DOS does not inherently imply simple (as you note); not in the day of DOS nor today; but a DOS is simple compared to any modern OS. And that is due to the ever increasing complexity of tech and that DOS is left behind; not an advancing tech. ... Here's a concern of mine: I don't want the reader to think that a modern OS might be considered a DOS just bc it supports disk storage. It might logically be defensible but it's not modern terminology/nomenclature. ... I'm sure there are better ways to get to the point I'm trying to make. But the current content ain't great. It needs improvement. Stevebroshar (talk) 12:10, 30 May 2025 (UTC)

Would you say that an Airbus is not an airplane because it is more complicated than 1950s airplanes? There is no reason not to use the term DOS for contemporary systems except for edge cases that run strictly from ROM. There's no functional difference among running from drum, disk or SSD. I'd prefer DASD Operating System, for exactly the reasons that IBM coined the term DASD in the first place. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 12:44, 30 May 2025 (UTC)

You make curios inferences. One need not remove to have a small version of something. Inferring that I'm claiming that DOS/360 is the result of removing stuff from OS/360, rather than that it's a separate, simpler operating system (which is what it is), is itself a curious inference. It's also not a correct inference, so you should abandon it.

WRT separation of OS from file system, DOS refers to an age gone by when there was less separation than today. To what sort of separation are you referring?

I don't want the reader to think that a modern OS might be considered a DOS just bc it supports disk storage. It might logically be defensible but it's not modern terminology/nomenclature. No, nobody use the term "DOS" these except to refer to old OSes with "DOS" in the name. The reason why it's perhaps not a good term for modern OSes is similar to the reason why "horseless carriage" is not a good term for modern automobiles - both terms emphasize characteristics that were significant then but not now; OSes with disk support may have been somewhat of a new and unusual thing for the platforms in question in the eras in question, but general-purpose OSes without support for direct-access storage devices these days are somewhere between extremely rare and non-existent (yes, an SSD is a DASD!), just as carriages that are propelled by horses rather than internal-combustion or electric motors are rare curiosities now.

The way to note that the term "DOS" is somewhat obsolescent, at least when talking about general-purpose OSes, is to note that it's a historical term. Fiddling with the definition to rule out modern OSes is anachronistic (e.g., "it's not a DOS if it supports SSDs") and may even be technically incorrect (e.g. "a DOS is something that only supports direct-access storage devices"), so it should not be done.

The term might still be relevant for small real-time OSes for embedded systems, as per Chatul's comments. I'm not sure it's used there, however; it may just be that those OSes can be configured at build time with features built in or omitted, and at least some of those OSes may be capable of being built with DASD support but aren't required to have DASD support, so you can omit it if you don't need it, to shrink the code size.

Perhaps another way of defining a DOS is as an OS that requires at least one form of DASD. Guy Harris (talk) 22:34, 30 May 2025 (UTC)

Although, in the era of diskless workstations, OSes that supported them would not, by that definition, be DOSes, even though they do require some form of file system support, even if it's only access to a file system on a network server, e.g. SunOS used NFS for most file access on diskless workstations. (Prior to SunOS 4.0, they also used the "ND" - Network Disk - protocol to access a chunk of disk on the server as if it's a disk; SunOS 4.0 got rid of ND and supported the root partition being mounted over NFS and supported NFS I/O to a "swap file" for backing store for pages not memory-mapped from a file.) Guy Harris (talk) 23:19, 30 May 2025 (UTC)

That is the same issue as drum and SSD. The system requires a DASD; it does not require that the DASD be a disk. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 09:28, 31 May 2025 (UTC)

Historically, there were systems that ran from tape but supported DASD, including disks. They were never referred to as disk operating systems. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 09:28, 31 May 2025 (UTC)

definition does not apply to modern os?

The introduction defines a disk operating system as one that can use a storage disk, presumably in contrast to punch cards etc. It then claims that "Strictly speaking, this definition does not apply to current generations of operating systems". However, most well-known modern operating systems support storage disks, file systems, booting from such disks etc. In fact, the only exceptions I can think of are embedded operating systems. Maybe the introduction should be changed to "Strictly speaking, this definition also applies to current generations of operating systems, such as versions of Microsoft Windows in use, but it is almost exclusively used for older generations of operating systems." 2A02:8070:E289:7500:75F8:2A20:E5DC:1067 (talk) 17:22, 9 February 2018 (UTC)

Many computers today use solid-state storage (i.e. SSD) instead of a disk storage. The modern OS supports storage on disk as well as solid-state tech. So, one could claim that a modern OS is a disk operating system since that is logically a subset of any modern OS. But, I think DOS was a term used to indicate support for disk storage in a day when disk storage was new tech; to differentiate an OS with disk support vs an OS that didn't support disk storage. Today, that distinction is not interesting since all modern OSes support disk storage (so highlighting the feature is not interesting or marketable) as well as newer storage tech (making disk storage support even less intersting/marketable). So, I'd say it's correct to say that a modern OS is not a DOS. Today, storage is very different than it was in the heyday of DOS systems. DOS is a historical term now. Stevebroshar (talk) 18:35, 16 May 2025 (UTC)

but that's not what DOS meant What did DOS mean?

not what DOS means And what does it mean now?

In the case of DOS/360, the "D" served at least two purposes: 1) distinguish it from OS/360 and 2) distinguish it from the variant TOS/360, for systems with tape but not disk (and from BOS/360, I guess). In that era, random-access storage devices (or, as IBM called them, direct-access storage devices or DASDs) were usually either disks, drums, or data cells.

In the case of microcomputers, it sounds as if it means "we don't just support cassette tapes, we support disks!" At that point, drums and data cells were dead, and SSDs weren't A Thing yet.

Now, maybe it's time to reintroduce the term DASD, or maybe RW-DASD so as to rule out CD-ROM, DVD-ROM, etc, and have it mean "FDDs, HDDs, and SSDs", and have the "D" in "DOS" stand for "DASD".

But, these days, few if any general-purpose OSes don't support "RW-DASD" storage, so they're mostly if not all "DOS"es. Guy Harris (talk) 18:59, 16 May 2025 (UTC)

I guess you are wondering or clarifying what I meant by "not what DOS meant... not what DOS means". I think you get my gist. Terms have shifting meanings over time, right? What a term meant in 1970 may not be what it means today. We can describe that it meant at different points in time and what it means today. IMO DOS is a historical term that has no meaning WRT modern computing systems. But, some might argue that a DOS is a subset of a modern OS since a modern OS supports disk storage. That is logical, but I don't think it lines up with modern nomenclature. ... I agree that DOS was a marketing term (as you say) to identify disk storage support. ... Never heard of DASD; I guess it's used in the mainframe world which I do not know of. The DASD article says "Later, optical disc drives and flash memory units are also classified as DASD" so it doesn't exclude CDROM/DVDROM. I guess that's why you say RW-DASD, but is that a thing (notable term)? But, if it includes flash, then I assume is also includes SSD. DASD is can of worms ... But, listing what types of disks are generally included by disk support implied by DOS is a reasonable addition. Stevebroshar (talk) 12:57, 29 May 2025 (UTC)

Aren't there operating systems for embedded systems that run out of ROM? Or has the low cost and small size of contemporary SSDs made them obsolete?

The term DASD is very much in use today.

Early systems running from tape,e.g., IBSYS, TOS/360, were never considered to be disk operating systems. The reference to obsolete technologies should mention drum storage instead. -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 14:11, 29 May 2025 (UTC)

What's an OS extension?

There's a section title: OS extensions. What does the term mean? It's not familiar to me WRT DOS. Stevebroshar (talk) 11:35, 20 May 2025 (UTC)

Maybe the editor considers BIOS to be an OS and BDOS to be an extension, but how many contemporary OSs still use BIOS services? Or maybe they consider UEFI to be an OS? -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 15:24, 20 May 2025 (UTC)

The terms "BIOS" and "BDOS" originated in CP/M, where they were both core components of the operating system, with the BIOS being the device drivers that manage he hardware and the BDOS implementing the file system (and some other OS services?). The BDOS wasn't an extension, it was part of the core OS.

The term "BIOS" got repurposed, in the IBM PC, to refer to a ROM-based set of device drivers and other code that provides services similar to what the operating system BIOS provided in CP/M. I have the impression DOS (as in PC-DOS and MS-DOS) used the ROM BIOS to do low-level disk I/O, but DOS included its own file system code, so DOS wasn't an extension to an OS, it was the OS, including the file system code.

I guess there may have been some OSes in which support for file systems on disks was an extension to the core OS, rather than part of the OS, but I suspect that's rare relative to the number of OSes with "DOS" in their name and with file system support being part of the OS. Guy Harris (talk) 18:11, 20 May 2025 (UTC)

I've been assuming that QDOS retained the BIOS/BDOS split of CP/M and that the BIOS in the PC ROM was the functional equivalent of BIOS in CP/M and QDOS. Does anybody know whether that is the case? -- Shmuel (Seymour J.) Metz Username:Chatul (talk) 20:37, 20 May 2025 (UTC)

(Presumably 86-DOS; QDOS is a disambiguation page.)

At least as I read the 86-DOS Programmer's Manual, it doesn't seem to have such a split - they don't mention any such a split, at least. Perhaps, as the idea was that it was an OS for SCP's computers, rather than an OS for arbitrary 8086/8088-based computers, they didn't need to have different BIOSes for different designs with different hardware. Guy Harris (talk) 21:56, 20 May 2025 (UTC)

What extension means is till vague to me. You use the term as if I know what it implies. Extension could mean lots of different things. It could mean it was added to the core product in a later release; the product was extended. It could mean that it's an optional feature that can be installed by the user post-production; post install. I could mean that it's part of the core product but can be enabled/disabled by the user. ... I think the article is over-organized ... as many lists are. I think the list should be flat. If extension is interesting for a particular item, then describe that for the item -- in detail about what extension means for that item. Stevebroshar (talk) 12:46, 29 May 2025 (UTC)

It could mean it was added to the core product in a later release; the product was extended. That's not how it's used, at least for Atari DOS.

It could mean that it's an optional feature that can be installed by the user post-production; post install. That appears to be how it's used for Atari DOS, although, in that case, it may even have been separately ordered rather than being shipped with the core OS.

I could mean that it's part of the core product but can be enabled/disabled by the user Again, not how it's used for Atari DOS.

Yes, the list needs work. Part of that would be putting all the ones in the second bucket together and, if any are left, putting them into separate buckets. Guy Harris (talk) 23:27, 29 May 2025 (UTC)

Interesting info about Atari DOS. IMO, the article should say that ... for Atari DOS ... something like it's an optional feature that can be installed by the user; post install. And yes, the lists should be merged and descriptions expanded to describe the OS-extension-ness of each. I would avoid other segregation. Segregation leads to awkward information -- like the current OS extension section. Better to tag than to segregate. Stevebroshar (talk) 12:02, 30 May 2025 (UTC)

References

Not all Disk Operating Systems are disk operating systems by this article's definition

The article now says that "A disk operating system (DOS) is a computer operating system that provides storage access limited to disk hardware (such as a floppy, hard drive and optical)".

DOS/360, despite having the full name "Disk Operating System/360", also supported named files on magnetic tape. (I'm not sure whether it supported drum or data cell storage.)

DEC's DOS for the PDP-11 also supported files on DECtape, and possibly also regular magnetic tape.

So not all operating systems named "Disk Operating System", or having "DOS" in the name, are disk operating systems. Guy Harris (talk) 18:56, 20 May 2025 (UTC)

The term disk operating system is nebulous ... as are many terms. For example, what is an operating system? We all know, but try to define it. ... I think the intent of 'limited to disk' is to exclude newer tech like SSD. But, you have noticed that it also excludes older tech like mag tape which of course not correct. ... Thing is, DOS is an obsolete term. It was popular and fashionable for a long time, but today is not spoken of. Is a modern OS a superset of a DOS and therefore is a DOS. Or is DOS something that only existed many years ago (and possibly today as a retro implementation of the now antiquated tech)? I doubt we can find a reliable, secondary source that clarifies that. I think DOS is a historical term that does not pertain to modern computing systems. IMO DOS describes operating systems that supported disk storage and possibly older storage tech, but not newer storage tech including solid-state storage. The term identified a new (at the time), major feature of an OS (disk storage) to differentiate it from older OS variants/versions that did not have this feature. But/and subsequent (more modern) OS variants/versions stopped using the term DOS since the disk storage feature became less interesting (and marketable) in light of other features being added to the OS (like GUI) ... FWIW I very much dislike the scope of List of disk operating systems called DOS since it implies that the name of something is important for categorizing it. It's not. There are characteristics that make something a disk operating system and its name is not one of them (or at least not top importance). Software can be a DOS without "DOS" in its name, and software with "DOS" in its name is not automatically a DOS. Stevebroshar (talk) 12:30, 29 May 2025 (UTC)

I think the intent of 'limited to disk' is to exclude newer tech like SSD. What factual basis supports your belief? SSD was neither significant when DOS/360 came out or when various microcomputer operating systems with "DOS" in their names came out, so I don't think you're correct in your belief.

The term identified a new (at the time), major feature of an OS (disk storage) to differentiate it from older OS variants/versions that did not have this feature. True at the time of DOS/360 - disks date back to the IBM 305 RAMAC, so it's not as if IBM had no disk-based systems prior to S/360, but systems such as IBSYS for the IBM 7090 primarily used tape. However, it's a bit weird in DOS/360 - as I understand it, the original idea was that OS/360 would be the one-and-only OS, but it was big and late, so they created a fallback family of smaller OSes, including DOS and the tape-only TOS/360, so there are other reasons for the "D".) Also true, I think, in the earlier minicomputer era, where disks weren't ubiquitous as they were costly, and the same applied later in the early microcomputer era.

Now, however, the term isn't much used, as most general-purpose computers have disks or some other form of random-access secondary storage ("direct-access storage devices" :-)). So it should probably speak of the term as being somewhat historical, used in eras when disk storage was rare for particular classes of machines. Guy Harris (talk) 23:10, 29 May 2025 (UTC)

WRT "I think the intent of 'limited to disk' is to exclude newer tech like SSD", no factual basis needed. I am interpreting the text of the article. I am not making claims about the topic (DOS). In fact, I'm saying that the article is trying to capture what you are saying! Yet, you seem unhappy with the current wording. Please re-word the article to be more clear. ... oh. so DOS/360 is a small version of OS/360? You seemed incredulous (in a different talk topic) that a DOS could be made by removing stuff from an OS, but apparently you can ;) ... I agree that the term is from an age gone by and that that should be highlighted in the article. Stevebroshar (talk) 12:22, 30 May 2025 (UTC)

no factual basis needed It's needed if you want me not to instantly reject the notion that any OS was called a "disk operating system" because it didn't support SSDs. Given that SSDs weren't a thing when any of the "DOS"es mentioned here were introduced, it's... unlikely that they used the term to indicate that SSDs weren't supported. If somebody interpret the article as making such a claim, it needs to be fixed so as to ensure nobody thinks in those terms.

so DOS/360 is a small version of OS/360? No, it's not. It's one of a pair operating systems, DOS/360 and TOS/360, designed separately from OS/360 for lower-end System/360s, with a minimum of 16KB. See Chapter 6, "Software Support", of IBM's 360 and Early 370 Systems for a history; at least some of the impetus for developing them may have been that IBM had, at the time, two main divisions responsible for computers - the General Products Division (GPD), which handled lower-end machines and the Data Processing Division (DPD), which handled high-end machines. OS/360 appears to have been a DPD project, and the GPD people were worried that it wouldn't fit on lower-end machines, so they came out with lower-end OSes - BPS/360 for 4K machines, BOS/360 for 8K machines, and DOS/360 and TOS/360 for 16K machines. The book in question says, on page 330, "The operating systems for 16K byte machines were built as two versions of one basic system and were named Tape Operating System (TOS) and Disk Operating System (DOS)."

The book doesn't say why TOS existed; I don't know whether magtape drives and media (tapes) were cheaper than disk drives and media (disk packs) at the time, although I suspect the media were cheaper. If so, they may have expected many buyers of 16KB machines to opt for tape rather than disk, especially if they were converting from tape-based systems; in practice, I don't think TOS lasted very long, but DOS and its successors continue to the present day with VSEⁿ (which IBM spun off to another company in the past few years), so TOS/360 was definitely a short-term stopgap, but not so much for DOS/360.

So, in this case, the "D" in "DOS" wasn't an indication of fewer capabilities, it was an indication of more capabilities, i.e. that it supported disks as well as tapes.

Similarly, DOS-11 was an early OS for the PDP-11; prior to that, I'm not sure there was much programming support for the PDP-11 other than "here's some stuff that reads source code from paper tape and punches out object code on paper tape", with software loaded from paper tape. The "D" in "DOS" is, again, not an indication of fewer capabiliies, it's an indication of more capabilities, i.e. that it supports files on disk. That may have been the case in other minicomputer-era DOSes.

It sounds as if the same applies to microcomputer-era DOSes.

So the article should indicate that a "disk operating system" is an operating system that supports disks, and that the term was mainly used in eras when disks weren't ubiquitous on the target machines for the DOSes, so "hey, this supports disks!" was a selling point. (That may even somewhat apply to DOS/360, as I suspect they didn't expect disks to be ubiquitous on the low-end S/360s. @Chatul: - does that make sense?) It should not say anything about it being an operating system that only supports disks, as I've seen precisely zero evidence for it ever being used in that sense. Guy Harris (talk) 21:45, 30 May 2025 (UTC)

Not just supports, but requires. TOS/360 supported disk drives, but didn't require them and couldn't run from them.

Yes, a disk pack was considerably more expensive than a reel of tape. — Preceding unsigned comment added by Chatul (talk • contribs) 10:30, 31 May 2025 (UTC)

So how about "A disk operating system (DOS) is a computer operating system that requires a disk or other direct-access storage device, such as a solid-state drive as secondary storage." After that, indicate that the term is, for general-purpose operating systems, historical. Guy Harris (talk) 16:53, 31 May 2025 (UTC)

Done. Guy Harris (talk) 22:21, 15 June 2025 (UTC)

References