It's now safe to turn off your computer

Question

One thing I remember very well from my childhood is the screen you got at the end of a shutdown process on old computers:

I don't know if this was a Windows 95/98/2000/ME only thing but I wonder why computers back in those days had to be turned off manually. Was it really that hard to implement a self shut-off? What is the reason it took quite long for computers to feature this?

@Geo... what are you talking about? If memory serves, that uses super high-resolution Mode-X 320x400! Surely a pixel density of the future? — Tommy, Jun 20 '18 at 14:21
Windows 2000 comes from the NT lineage (it's the version of Windows NT in between NT 4.0 and Windows XP), not from the Windows 3.x/95/98/ME lineage. Windows 2000 and Windows ME hit the market at around the same time. — user, Jun 20 '18 at 14:52
@Geo... If this is what makes you feel old, you're way overdue for feeling old. — jpmc26, Jun 20 '18 at 19:22
Raymond Chen had written an article about this as well. The "dialog" is present in Windows XP as well, and may even exist in newer version of Windows (a SO user says forcing no shutdown works on Windows 10). I don't have an extra computer to see if there is a visible screen though. — Justine Krejcha, Jun 20 '18 at 22:31
@geo you're not old unless you had to run PARK.COM before turning off the power. — Criggie, Jun 21 '18 at 12:48
@JustinKrejcha as it was retained in embedded XP systems (which sometimes need their routine power-off to really cut the mains power to the enclosure) I wouldn't be at all surprised if it was present in newer systems. You could probably test it on 7 etc. by installing windows with ACPI disabled in the BIOS (not exactly a universal option, but it does exist) — Chris H, Jun 21 '18 at 13:32
I had an Epson Equity II back in the day, probably about 1986 or so, and it had software power off. — Brian Minton, Jun 21 '18 at 14:33
The message is still dangerously wrong. "It's now safe to turn off your computer". How does it know? This is Steve's computer. My computer is on the other side of the room. Ah well, I guess it's safe to go power it off... — jcoder, Jun 21 '18 at 14:57
The question title, and the picture below, made me feel as though I had suddenly been transported 15+ years back to my childood... This is like the last time I recently heard the sound of a dial-up tone, it was like it activated a portion of my brain that had been dormant for over a decade and it felt so bizarre and confusing and I didn't know what was going on until I was reminded of what it was, and I was still freaking out. — silvascientist, Jun 22 '18 at 21:53
Designers felt that users should have some control over that devilish machine. — Hot Licks, Jun 24 '18 at 13:32
@PaŭloEbermann in Windows 98 you can replace both the startup and the shutdown images — phuclv, Jun 24 '18 at 15:27
I suspect this may also be related to the need to 'park' older harddisks: https://retrocomputing.stackexchange.com/q/11545 — Frerich Raabe, Apr 15 '21 at 09:52
I've seen this screen on Windows XP. I had a screenshot of it for while but I lost it. — Joshua, Dec 14 '22 at 04:01

score 180 · Accepted Answer · edited Nov 01 '22 at 16:51

180

TL;DR: it took a long time (on PCs) because the industry wasn’t ready to push it. Scroll down to “Why did it take so long?” for details.

Shutdown screens

That screen comes from Windows 95 and its successors, 98 and Me. Windows NT showed a plain dialog box with a “Restart” button. Other operating systems which cared about managing the shutdown process had equivalents — OS/2 for example, and all the Unix variants (sometimes it was only a text message on the console). Raymond Chen wrote an amusing blog post illustrating the importance of the instructions in the shutdown screen.

Some history...

Before 1995 and the adoption of the ATX standard, the vast majority of desktop PCs had power switches which were directly connected to the power supply, and acted as mechanical switches only, interrupting the electric circuit when opened. It was therefore impossible for software to control the state of the power supply. But that wasn’t much of a problem initially: when the IBM PC was designed, storage media (including hard drives) had no caches, so when the hardware told the operating system that a write was finished, it really was. Under DOS, the kernel and shell worked together to ensure that when the DOS prompt was displayed, all the buffers were flushed; when software caches appeared, they adhered to this too (at least, the well-behaved ones did). Users were taught to exit programs, wait for the prompt, and wait for drive lights to switch off before powering the system down. (They might also need to PARK the drive heads but that’s another story.) Even with pre-95 versions Windows, users exited to DOS before switching the system off.

Windows 95 and other multi-tasking operating systems changed the picture: they didn’t “exit to DOS” on shutdown (either because they weren’t supposed to, or because there was no DOS to return to), so users couldn’t wait for a prompt to appear before switching off. In most truly multi-tasking systems there’s never really a quiescent state where the system is safe to power off, in normal operation; so most multi-tasking operating systems have a way for the user to say “I want to power the system down, prepare to do so”, and the operating system then needs to tell the user when it’s safe to power off. This ensures that all applications have finished writing the user’s files to disk, and that the system is in a consistent state (ignoring hard drive caches here...).

Shutting down PCs

Two features brought system power under operating system control: APM on the one hand, and ATX on the other. APM, which was designed for laptops initially, provided mechanisms for software to request changes in the system’s power state: fully on, in standby, suspended, or off. ATX changed the physical connections in the system so that power control became possible everywhere: it required that the power button no longer be a switch directly connected to the power supply, but instead that it be connected to the motherboard, and that the motherboard control the power supply itself. The power supply was also changed so that it would supply a small amount of current all the time, allowing the system to be left in “soft off” status, i.e. with enough capabilities to turn itself back on again when requested to do so.

You can see an example of the use of APM to power off a PC in Shutdown, a small assembly-language program written for DOS. Operating systems such as Windows 95 (with the APM drivers installed) would do the same thing.

It was quite exciting (to me anyway) to see APM and ATX roll out progressively in the second half of the nineties, and see systems suddenly acquire the ability to turn themselves off without human intervention, and to turn themselves back on at the press of a key on some systems. This was yet another sign of PCs “growing up” (“real” computers, i.e. Unix workstations in my mind at the time, had had the ability for a while, as had Macs).

Why did it take so long?

All this doesn’t address the actual question:

Was it really that hard to implement a self shut-off? What is the reason it took quite long for computers to feature this.

If you design it in from the start, it’s not all that hard to implement self shut-off, and many systems existed with this ability quite a few years before the PC acquired it.

I think the main reason it took so long is industry fragmentation. IBM designed the first PCs, and the majority of clones in the eighties and early nineties followed the blueprint set by the AT (or rather, the Baby-AT variant and LPX power supplies). But IBM moved on to the PS/2, which was a rather proprietary derivative of the PC, and left the rest of the industry to fend for itself. There was no real driver for big changes for many years: people continued using DOS, on its own then with Windows, and while there were other operating systems, none of them was successful enough to be able to drive change. No hardware manufacturer was dominant enough either. Various ad hoc consortia were created, e.g. for EMS (Lotus, Intel, and Microsoft), and more markedly when it comes to hardware, EISA (the “Gang of Nine”, led by Compaq), VESA, etc. Various de facto standards emerged, but no one was defining the PC platform, and operating system-controlled power-off wasn’t an important enough feature to mobilise the industry.

In the early nineties, surprising as it may seem now, there was a fair amount of uncertainty as to what the computing future held. Apple was making its comeback with cheaper Macs, workstation manufacturers were releasing lower-priced systems (or rather, not-so-expensive systems), a variety of operating systems and platforms were vying for attention (Be, RiscPC...), IBM was still pushing OS/2 and Taligent, Microsoft was pushing Windows NT, etc.

Eventually an alliance of companies took it upon itself to “remedy” this situation: Intel and Microsoft (referred to at the time as Wintel). This started in the early nineties, but wasn’t a done deal for quite a while; when ATX was published in 1995 (by Intel on its own), pundits liked it but weren’t sure it would convince the industry, although they were proved wrong fairly quickly. Windows 95 sealed the deal though and Intel and Microsoft became the definers of the PC platform (with the PC System Design Guide in particular).

On to the present day

APM is now obsolete, and ACPI is the interface which provides access to the power state nowadays (and many other aspects of the system). Pressing the power switch now only informs the system that the button was pressed, and it’s up to whatever’s controlling the system at that point to decide what to do with that information — which is nice because you no longer risk losing your work if someone accidentally presses the button!

(PCs never acquired the other hardware feature I wanted from Macs and Unix workstations, which was the ability to eject floppies without human intervention. Oh well...)

edited Nov 01 '22 at 16:51

user3840170

23,072
4
91
150

answered Jun 20 '18 at 08:01

Stephen Kitt

121,835
17
505
462

3

I guess tehre are different opinions on the usefulness. Well, I still not like the way the power 'switch' is implemented, as it's not a real off state, more of a reduced power state, where in fact I want the machine go off. The solution used by the original Siemens PC-D (inherited from the related Unix workstation) was wa more elegant. Here software couldn't switch off the PC, but prevent switching off. Serves the same purpose to avoide inconsistant data during shutdown, but when switched off, it realy was off, as the holding circuit was part of the mains side bridgeing the mechanical switch. – Raffzahn Jun 20 '18 at 08:25
4

@Raffzahn I agree that the usefulness of “soft off” is limited, there aren’t many PCs which need to switch themselves back on. I flip the power switch on the PSU once my non-BMC-controlled systems are off ;-). – Stephen Kitt Jun 20 '18 at 08:28
25

It took quite a long time (and a lot of nasty data losses) until the industry had educated the users that you simply shouldn't switch off a Windows (or Unix, for that matter) system while it's still running, but rather have to put it into an orderly shutdown - DOS users were used to flip their switches whenever they saw the DOS prompt. Once you tell people "never switch off your computer", you obviously need to tell them somehow when it's safe to do the opposite. – tofro Jun 20 '18 at 10:51
6

The Amiga was a multitasking system with hard-switched PSU. The correct procedure was to watch for indication on the drive LEDs that disk activity had completed, then switch off. I think all in-built disk caches were write-through. – Brian H Jun 20 '18 at 14:18
Good point @Brian, thanks; I’ve updated my answer to say “most”... – Stephen Kitt Jun 20 '18 at 14:53
12

IIRC it was, at least in some circumstances, possible to execute DOS commands when Windows 95 displayed the "it's now safe to turn off your computer" image because what it really did under the hood was to exit to a DOS prompt, but leave the monitor in graphics mode. So if you wanted to, you could in principle type WIN and hit Enter to restart the GUI. Not sure how well that worked in practice. – user Jun 20 '18 at 14:55
2

That does ring a bell @Michael... My point was that, from a user’s perspective, there was no safe place to switch off without an explicit screen, at least if Microsoft wanted to maintain the illusion of a 100% GUI operating system ;-). – Stephen Kitt Jun 20 '18 at 15:21
Another feature Macs had, in addition to turning themselves off, was that you could schedule a time for the computer to turn itself on - say in the middle of the night - with no human intervention required. – Glen Yates Jun 20 '18 at 15:37
2

@StephenKitt Soft off isn't the primary feature that justifies soft power control, it is sleep mode, which is essentially soft off with the memory kept alive. The whole change was driven by Energy Star requirements, and the fact that the US Government requires Energy Star in any computer they buy. – user71659 Jun 20 '18 at 15:42
@user71659 ATX doesn’t mention a “primary feature”, it lumps them all together as example uses for +5VSB: “Example uses include soft power control, Wake on LAN, wake-on-modem, intrusion detection, or suspend state activities.” I agree that sleep mode is very useful nowadays, but in early APM/ATX systems it wasn’t reliable enough and wasn’t used much in practice. – Stephen Kitt Jun 20 '18 at 15:50
Sleep mode was perfectly doable without removing the hard power switch. It's all the other creepy stuff that motivated removal of the hard power switch. – R.. GitHub STOP HELPING ICE Jun 20 '18 at 17:13
3

@R.. In fairness, I don't think I've had a PC PSU in the last well over a decade that hasn't had a physical AC-mains in-line power switch. It's just small and, in most circumstances, awkward to reach. But it's definitely there, and with decent BIOSes, nothing prevents you from setting the computer up such that it is usable as the primary means of turning the computer on and off... – user Jun 20 '18 at 17:50
@MichaelKjörling: Current laptops certainly don't. My first 2+ laptops did. I don't recall what PC PSUs do since I haven't used one in decades; all my boxes have picoPSU or other DC-DC power supplies. – R.. GitHub STOP HELPING ICE Jun 20 '18 at 18:21
@R.. "laptops" Fair enough, I didn't consider that case. – user Jun 20 '18 at 18:23
2

Even this answer makes me feel old! It only goes back as far as "earlier versions of Windows" and computers with hard drives! The first computers I used had no hard drives and you couldn't "exit to DOS" in many cases because a lot of software shipped on bootable floppies! You just put in the floppy, turned it on, waited, did whatever, and then turned it off. A lot of early software loaded itself completely into RAM and if you didn't want to save anything, you could turn off the computer at any time. – Todd Wilcox Jun 20 '18 at 18:36
1

@Todd perhaps you missed the part about “when the IBM PC was designed” ;-). My first PC only had one floppy drive too, but most of the time I wanted to save what I had worked on so I paid careful attention to the floppy light... (I had an 8-bit Atari before that, with no storage.) – Stephen Kitt Jun 20 '18 at 18:45
1

Sadly, the meaning of the "Big Red Switch" seems to have been lost on the younger generations. – Adrien Jun 20 '18 at 19:15
1

Answer needs a TL;DR so that we can tell where it's going. – jpmc26 Jun 20 '18 at 19:23
The screen also exists on Windows XP (and some Longhorn builds) as well, although it has no options to restart – Justine Krejcha Jun 20 '18 at 22:32
@JustinKrejcha yes, if you install XP on a PC with AT power supply it'll display that message – phuclv Jun 21 '18 at 07:12
@MichaelKjörling I guess you build your PCs (or buy ones built with high-spec components) then. Many built-to-a-budget systems I've used omit the physical power switch on the PSU – Chris H Jun 21 '18 at 13:34
@MichaelKjörling it's actually quite easy to find such switchless PSUs even today: e.g. Gembird CCC-PSU-BBP-600. You'll find them basically in any large enough computer parts shop. – Ruslan Jun 21 '18 at 13:55
@jpmc26: tl;dr people wasted less energy back in the day. – user541686 Jun 21 '18 at 18:02
2

I'm still waiting for the USB stick ejector ... – Paŭlo Ebermann Jun 21 '18 at 21:47
10

"PCs never acquired the other hardware feature I wanted from Macs and Unix workstations, which was the ability to eject floppies without human intervention" With the ever intuitive process of dragging the floppy icon to the trash can. – Andy Jun 22 '18 at 15:04
1

"which is nice because you no longer risk losing your work if someone accidentally presses the button!". Not entirely true, my toddlers seem to have ben really good at pressing the button for more than four seconds. Although you can argue that it's not entirely "accidental". – Martin Argerami Jun 23 '18 at 17:38
@Martin right, it seems to me a four-second (or ten-second on some systems I’ve seen recently) no longer qualifies as accidental! – Stephen Kitt Jun 23 '18 at 18:53
@MichaelKjörling It's far too long to remember the specifics, but I once had my Windows 95 98 machines Set up to boot to a command prompt , Where you could type "win" To start the main OS and then when you did shut down it would drop you back at the command prompt – Weaver Jun 25 '18 at 03:25
"Pressing the power switch now only informs the system that the button was pressed" – is this also true for the long power switch press you do when your OS is frozen? Or is this event handled by the hardware? – Schmuddi Sep 05 '19 at 09:29
2

@Schmuddi the long power switch press isn’t handled by the OS; it’s probably handled by the motherboard controller, since it’s configurable on many systems, but I’m not 100% sure (the other option is that it’s controlled in the PSU). – Stephen Kitt Sep 05 '19 at 09:43
2

@StephenKitt I'd assume soft off with the ability to turn itself back on is mostly used for Wake-on-LAN update roll-outs in enterprise settings... and the SKUs I tend to see being pitched at that market segment have power supplies with no physical switch, where the only way to get a true "hard off" state is to pull the power cable. (An idiot-resistance design decision, I'm sure. You don't want the employees "helpfully saving power" and messing up your update roll-out.) – ssokolow May 27 '20 at 18:26
@ssokolow all ATX systems work that way, and yes, I suppose it gets most use in enterprise settings with WoL. It also enables power-on by keyboard, by alarms, and perhaps others I’m not thinking of now... – Stephen Kitt May 27 '20 at 18:49
@StephenKitt Obviously all ATX supplies go to standby rather than true off. I meant that, if a SKU is potentially going to be attractive to enterprise customers, you can bet Dell or whoever are going to pick/build an ATX power supply with no physical cut-off that could be attractive to an employee trying to be "helpful" before leaving for the day. – ssokolow May 28 '20 at 00:40
@ssokolow ah, yes, I agree! – Stephen Kitt May 28 '20 at 05:10
Power down screens are at least as old as the System/x midrange series of IBM. IBM did not build the PCs as most other microcomputer manufacturers did... some hardware design decisions when making the 5150 were made with the midrange series in mind. Those then influence how the software would eventually be. – Borg Drone Dec 07 '22 at 09:59
Ah yes, the "Please turn off" switch as we called it when it was new. – Wildcat Matt Dec 07 '22 at 16:37
"PCs never acquired the other hardware feature I wanted from Macs and Unix workstations, which was the ability to eject floppies without human intervention" the LS-120 drive could eject floppies based on a software command. – Peter Green Jan 16 '23 at 18:13
TIL, thanks @PeterGreen! – Stephen Kitt Jan 16 '23 at 19:33

Graham · Answer 2 · 2018-06-20T20:15:25.033

55

Was it really that hard to implement a self shut-off?

Yes. Yes it was.

Until Windows 95, all power switches were that - a switch. On or off, nothing else, and there was no "self shut-off". Nor was there a requirement for it.

The advent of Windows 95 and the possibility of the system saving state before shutting down cleanly created a market requirement for power-off to be controlled by software. This led to the development of the standardised ACPI interface and ATX power supplies to implement the new requirement, a year after Win95 had exposed the need for it.

But until this had been designed, implemented in the OS, and implemented in the BIOS, of course the only way of powering off your PC was with the on/off switch. Hence the famous message.

edited Jun 20 '18 at 20:15

answered Jun 20 '18 at 17:30

Graham

2,054
8
11

15

Under DOS the file system was always up to date, so you didn't have to go through a shutdown procedure. All you had to do was turn the thing off. What's what Windows 95 changed, and the hardware eventually changed to match. +1. – Pete Becker Jun 21 '18 at 16:57
1

Wow, I had no idea about this. This seems like the real answer. Thanks! +1 – user541686 Jun 21 '18 at 18:08
6

@PeteBecker : That depends. SMARTDRV /N much? docs – Eric Towers Jun 22 '18 at 02:12
2

@Pete Becker - That's what I always thought - to save disk cache in memory. There where two exceptions. After disk compression started to be used on DOS machines, turning the computer off during encryption or compression could render the entire hard drive useless. You just waited until the drive light stopped flickering. – jwzumwalt Jun 22 '18 at 05:08
Surely it was windows 95! No other operating systems existed at the time. The reason is disk caching. Regardless of operating systems. – akostadinov Jun 22 '18 at 10:28
4

@jwzumwalt -- good point about disk compression. My rule was to wait until everything I'd started had finished before turning the machine off. The change with Windows was that you also had to wait until everything Windows had started had finished. – Pete Becker Jun 22 '18 at 15:25
1

@Pete On the early days of hard drives in PC, you had to park the head of the hard drives manually before shutting down (using some kind of utility typically called "hdpark"). Well, actually, now that I think about it, I'm not sure it was really necessary, but I know my father really insisted that we did it each and every time... – dim Jun 25 '18 at 20:21
APM existed years before ACPI, and it already has commands for shutdown. – Ruslan May 26 '20 at 13:00
@Ruslan True, but no desktop PC power supply existed which allowed shutdown from BIOS. All desktops used the standard AT power supply which had no ability for the mobo to control it. Even laptops (which all had custom power supplies of course) often didn't either because it added complexity and hence cost, for a feature which pre-Win95 was simply not relevant. ATX PSUs were the point where this became available in power supplies and mobos. APM was still relevant, sure, but better integration with the OS meant that the wider feature set of ACPI was needed. – Graham May 26 '20 at 13:18
@dim those were pre-IDE drives, back in the MFM/RLL days. – RonJohn Sep 06 '22 at 05:55

user · Answer 3 · 2018-06-20T10:11:52.903

14

The versions of Windows that displayed that message used the FAT filesystem. FAT does not have any atomic write capability - that is, if power is lost while data is being written it can corrupt the filesystem. This was such a common problem that Microsoft included a tool (chkdsk) that would detect and attempt to fix it every time the machine booted.

To avoid this happening users were told not to simply turn their computers off. Other systems around at that time, such as the Amiga, Mac and DOS based PCs, could simply be turned off when the user was finished using them, with a few caveats such as waiting for floppy drive lights to go out. Windows 95 introduced virtual memory and write caching for performance reasons, which required a clean shut down to avoid filesystem corruption.

Since older AT machines could not power themselves off like newer ATX ones could, Windows would display this message when it was ready to be switched off.

edited Jun 20 '18 at 10:11

answered Jun 20 '18 at 08:52

user

15,213
3
35
69

10

Corruption is a possibility in any system when powered off without warning, regardless of the file system — some file systems handle it better than others, but there’s no absolute guarantee. Also, Macs couldn’t be switched off just like that, you had to shut them down properly. The page file wasn’t a source of corruption because its allocation never changed (and that’s what FAT cares about). – Stephen Kitt Jun 20 '18 at 09:15
6

@StephenKitt Corruption at the file system level is not nearly as big a deal as corruption at the application level. I've never seen corruption of the file system arising from sudden power loss that couldn't be fixed with fsck or equivalent. But if you pull the plug before the application has finished saving your data or before the data has been flushed from the cache onto the physical disk, you will never see that data again. Furhthermore, it could leave you with files that are perfectly fine at the file system level but corrupted from the application's POV. – JeremyP Jun 20 '18 at 09:49
2

@JeremyP agreed, I wasn’t trying to write a treatise on the consequences of pulling the plug in my comment; I was reacting to user’s implicit claim that other file systems provide power-off protection. – Stephen Kitt Jun 20 '18 at 09:52
1

@StephenKitt actually we have had atomic filesystems for decades, which can handle sudden loss of power for a small performance hit. In fact, Microsoft's own NTFS is an example and was one of the major improvements introduced with Windows XP. – user Jun 20 '18 at 10:13
3

@user we have had file systems with atomic semantics for decades, but no file system can fully handle sudden loss of power on its own. Systems which handle loss of power have additional hardware to do so: UPSs, disk caches with battery backups or flash storage, etc. Current Windows still runs its version of CHKDSK on boot; if it was truly resistant as you claim, it wouldn’t need to... In any case, JeremyP’s point stands, and file system coherence isn’t sufficient — you need the applications to have finished writing too. – Stephen Kitt Jun 20 '18 at 10:29
4

@user The logging feature of the modern Windows NTFS implementation only protects metadata, not the data in files themselves. Unexpected power loss can still cause corruption of data. – Jun 20 '18 at 14:53
Yes, that's why I said that the filesystem can be corrupted. The data stored is separate. – user Jun 20 '18 at 15:58
Not too many months ago I tested a so called "Uninterruptible Power Supply" that displayed 100% battery by unplugging it from the mains. My Windows 7 PC was utterly corrupted and after wasting a day or two messing with everything from recover discs to boot sector tools, I finally gave in an reinstalled the operating system, cursing then UPS manufacturer all the while. Just sayin'. – MickeyfAgain_BeforeExitOfSO Jun 20 '18 at 17:35
3

@user "In fact, Microsoft's own NTFS is an example and was one of the major improvements introduced with Windows XP." NTFS was introduced with Windows NT 3.1 (the initial Windows NT release) in 1993. Windows XP was the first version of Windows NT that was targetted toward the consumer market; earlier versions were targetted more toward servers and higher-end personal workstations, typically at mid-size and up businesses not least because it was quite a resource-hungry OS and didn't run non-trivial DOS software well. IIRC Windows 2000 (RTM'd in late 1999) was the first to run games decently. – user Jun 20 '18 at 17:43
7

An important difference between Windows 95 and most common Windows 3.1 installations is that the latter would generally only write to disk in response to user actions; the system would be unlikely to spontaneously start writing data to disk at unpredictable times. Under Windows 95, there was no general way to predict whether the system might start writing data to disk just as one was about to hit the switch. – supercat Jun 20 '18 at 21:27
2

@mickeyf lesson learned - next time test it with a lamp. – user253751 Jun 20 '18 at 22:38
@MichaelKjörling I know, but XP was the first time it was introduced on the consumer side as a replacement for FAT. On the consumer side it's predecessor was Windows ME, which used FAT32. – user Jun 21 '18 at 07:54
5

"I've never seen corruption of the file system arising from sudden power loss that couldn't be fixed with fsck or equivalent." If your definition of "fix" includes "lose files" then maybe, but otherwise you've been extraordinarily lucky. – user541686 Jun 21 '18 at 18:11
@user541686 That's not corruption at the file system level. – JeremyP Sep 08 '22 at 15:41
@JeremyP: the FS corruption is what causes fsck to unlink files. – user541686 Sep 09 '22 at 14:04
@user541686 After running fsck, the file system is no longer corrupt. That's what I said. I've never seen fsck delete a file that had been completely written to the file system including its directory entry. – JeremyP Sep 12 '22 at 10:35

Peter Parker · Answer 4 · 2018-06-22T09:33:52.640

2

This was purely a PC thing. Older retro computers (8/16 Bit Homecomputer) had always physical switches you needed to operate manually. Also as they were missing HDs, you could switch them off anytime (risking only to break the current floppy if it was just written to).

PC was build from standard components and a lot of manufacturers needed to cooperate:

mainboards needed to support the feature
cases needed to support that "new powerswitch"
OS needs to have a "driver" to switch off and on
CPU (?)
may forgot more components here

The first implementation was called APM (Advanced Power Management) and was defined by Microsoft and Intel in January 1992 (1.0), 1.1 was released in September 1993 and 1.2 was released in 1996.
APM was succeeded by ACPI(Advanced Configuration and Power Interface) in December 1996 which also added functions for HW detection (for example Multiprocessor environment and Plug and Play).

edited Jun 22 '18 at 09:33

answered Jun 20 '18 at 07:30

Peter Parker

1,025
8
13

8

This answer is really vague and you haven't talked about ATX motherboard which was a game changer for such feature. – Eric Cartman Jun 20 '18 at 07:57
7

The Macintosh II had a software power-off function in 1988. One common source of annoyance was that the shutdown and restart options were right next to each other, so if the mouse slipped while trying to select "Shut off", one would have to wait for a reboot before trying again. One clever solution to this was an INIT (startup program) which would check if Option was held, and shut off the system if so. In any case, all of this came long before Windows 95. – supercat Jun 20 '18 at 14:49
1

I'm pretty sure APM allowed for software to turn off the computer, and APM came before ACPI. – user Jun 20 '18 at 17:45
@Michael yes, APM 1.2 provided this ability, ten months before ACPI was published. – Stephen Kitt Jun 21 '18 at 18:11
1

I think this is the best and most clear answer, despite the voting scores. It is particularly funny that the topvoted answer thinks that ATX was created by the Win95... – peterh Jun 23 '18 at 01:24
1

@peterh where does my answer say that ATX was created by Windows 95? – Stephen Kitt Jun 23 '18 at 18:55
@supercat: That's why I started with "This was purely a PC thing": Apple as a HW-Manufacturer was easily able to provide the technology in their own machines much earlier, as they did not need to agree on standards with OEMs. – Peter Parker Jul 11 '18 at 08:32
1

@PeterParker: The Macintosh II had power-cycling hardware, but the Macintosh SE and Macintosh Plus would display "It is now safe to turn off your Macintosh". – supercat Jul 11 '18 at 14:41
I wouldn't call this answer as "correct" because of the statement it was only something that happened with PCs. In reality it was more related to the IBM world as previous (and other then contemporaneous) systems of the same brand had the shutdown sequence first triggered from software and then requiring a manual power shutdown. Then came the PC clones and extended the issue, until a complete software-triggered power supply shutdown was implemented. – Borg Drone Dec 07 '22 at 09:50

score 1 · Answer 5 · answered Dec 07 '22 at 14:50

Safe shut down screens exist at least from the 70s. It was not something neither the PCs, Apple or any other microcomputer-based company introduced.

While I personally don't know who introduced it, IBM midrange series System/x may. During mid-to-late seventies, IBM sought to create a microcomputer to introduce at the low spectrum of the market while having institutions and medium companies to rely on the System/3, System/32, System/34, System/36, System/38 and later AS/400. But at first IBM engineers did not have expertise with microprocessors and designed both the System/23 Datamaster and the original 5150 PC with both concepts of terminals and minicomputers alike.

Talking at least in behalf of the S/36 it has a command to turn off, which triggers a process which saves the state of the system, then displays the safe turn off screen and waits for the technicians to disconnect it from power using a mechanical switch.

In the case of the PC I think they at first didn't expect or were willing to give them functionalities close to the S/36 compact such as having hard drive and later save the system state at turn off. When they introduced the 5150 most competing microcomputers didn't have an integrated floppy drive or any kind of drive at all therefore for them introducing the system without hard drive and dual floppy drive was a working strategy.

Eventually the PC world grew due to clones and IBM lost control over their own standard and eventually developers realized having a command to shutdown without turning the computer off seemed an incomplete task and therefore adapted the power supplies to turn on/off with software-controlled strobes.