Why Windows 95 left a handy power saving feature on the cutting-room floor Microsoft vet Raymond Chen first told the story of HLT and Windows 95 more than 20 years ago. The instruction tells the CPU to effectively shut itself down until the next hardware interrupt – ideal for laptops, since power consumption would be hugely reduced. Microsoft had it implemented and working in Windows 95, but found …
The power of competition, I guess?
Windows 95 must have felt far from a sure-fire thing when development began: it provides a bridge towards a modern OS while retaining full backward compatibility — including support for devices with only DOS drivers — without incurring anything beyond a regular generational speed penalty, despite the underlying hardware being all over the map. And that's against IBM which already has a full modern OS on the market for the same hardware, without the legacy baggage.
Modern Windows development must feel like a walk in the park.
In terms of desktops I have found that often the first sign of a failing power supply is loss of always-on USB ports and kept-alive LAN ports. I use Wake on LAN quite a lot so notice this. The computer is usually otherwise perfectly healthy but sooner or later (could be many months) it will fail to start at all. New power supply cures all.
M.
"The first sign of a failing power supply is loss of always-on USB ports and kept-alive LAN ports"
The always-on and keep-alive ports are powered by the 5 volt standby power supply which is a separate set of circuitry inside the power supply case. So that will have failed in your case.
Yeah, though the exact topology probably depends on the supply and there may be some shared parts. Not sure why manufacturers should skimp on the components of what should be a very simple, low power, section, but that's what seems to be the case. Anyway, very useful for me because it means I can change the power supply before the computer fails altogether :-)
M.
Check Windows and BIOS settings. In Windows the "device can wake up the PC" must be checked too, not only the BIOS setting.
Additionally: If you have a USB hub between your computer and the mouse/keyboard it may not work too, since the hub draws too much power or does not handle the sleep-wakeup correctly. Same goes for some wireless mice and some gamer-RGB-1000Hz USB keyboards which draw too much to work on standby power.
If you have a simple keyboard without any bells and whistles, usually the 20€ to 40€ range, test with that one whether it will wake up the machine.
Brings back memories. Someone wrote an application to make use of this where WIndows didn't
It was called 'RAIN' that you ran at idle priority and it chucked HLT instructions at the CPU. I just found it for download on a site that makes me wish plain flat HTML sites were a thing still.
Which didn't make sense at all. The people getting those halt enabling bits of code didn't have any idea whether their CPU was one of the "bad" ones that locked up in response to a HLT instruction. They'd found out if they tried it. Microsoft could have built the HLT thing into Win95 but left it disabled by default. People hear "hey you'll save battery if you enable power savings in Settings" and they'll try it and find out whether it works or not.
TESTING is a thing you can and should do with software like this.
1. Boot DOS.
2. At the DOS prompt, run the executable (the one I have is called IDLE.EXE).
3. Did your computer lock up?
3a. Yes: don't use this program on your particular computer. Reboot.
3b. No: put this program in your AUTOEXEC.BAT file or Win95 Startup programs folder as appropriate.
I don't expect home users to figure out this test, but do expect competent techs to do so!
I'll note the HLT instruction actually ONLY halted the CPU until an interrupt came in (no power saving mode) on anything before the 486DX4 (marketing at it's finest, this was a clock tripled CPU not quadrupled as the DX4 name would imply.). Not a common chip so basically the Pentium. So on many Win95 machines this wouldn't have even saved power.
Also, shocking given modern CPUs but that 486 used like 3 watts and Pentium 90 7.5 watt TDP so it's not like now where a 'lower powered' Intel CPU (other than Celeron N) would use like 30 watts without power saving.
We had NIMH batteries in laptops back then, so while saving a piece of 7.5 watts doesn't sound like much versus today you gotta remember how much less power laptop batteries stored, even despite their larger size. There were fewer "other" things taking up battery too. No wifi, no bluetooth, no USB ports providing power to attached devices.
486 used like 3 watts
and if I remember correctly, the StrogARM 110, released around the same time as the DX4, which ran at a faster ~200MHz clock and beat any 486 for raw (integer) computing power used 600mW at full whack and came in a plastic package with no additional cooling, whereas the later 486es needed huge ceramic packages and some people started fitting passive heatsinks. Certainly in a laptop they benefitted from additional cooling.
Small wonder ARM gained a foothold in mobile devices!
M.
The first generation AMD Ryzen CPUs basically did the same thing due to a bug in the deepest sleep state. Funnily enough, this was never noticed with Windows, not because they hadn't implemented it, but simply because it never gets that idle. XD It only became apparent after release when people like me started using them with Linux.
"The problem, Chen explained, was that "it was a brick until restart, but it restarts into a brick! The OS boots into a brick.""
Surely there is a way to stop that. It's year since I did any programming but...
Set a test flag saved to disc that you are about to use HLT
Use HLT
If you are able to restart you will now know that HLT can be used and set flag so HLT is used and you clear test flag.
On subsequent boot, look for test flag if set then you know HLT can't ever be used.
Is sometimes a wonder for but also sad feeling. I'd like to go back to those days but also want to continue with the PC tech we have now.
So much so I found myself watching the whole of the
Windows 95 Traincast training vids on YouTube restored by Blue OS Museum. Its seems like such a world away now.
I remember when we finally got a decent PC that could do sound and had Windows 95 pre-installed. I looked over the CD in awe of the sounds and movie clips I could finally play and with sound. So every time I hear Edie Brickell - Good Times I get the rush of nostalgia. Back in the old, long gone family home, upstairs with this new PC, while still doing my IT course at college. It was amazing.
I've always liked Windows, its just sad how Satnav is ruining it all.
I'll get my coat.
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