Why does my hard drive light flash every few second?


Back in Windows 95, people would notice that their hard drive light would blink every few seconds. What's that all about?

Actually, it wasn't the hard drive light after all.

Windows 95 was polling your CD-ROM drive to see whether you had inserted a new CD. Some computers wired up the "hard drive light" not to the hard drive but rather to the SCSI and/or IDE bus. So the light didn't indicate hard drive activity necessarily. It turned on for any bus activity.

Fortunately, motherboard manufacturers discovered their mistake and nowadays you don't find any of them that miswire the hard drive access light.

Or do you? I keep my computer under my desk so I never see the hard drive light anyway. I'm just surmising that in the past seven years, motherboard manufacturers have gotten their act together.

Comments (22)
  1. Anonymous says:

    So why does my Win2000 Pro machine do that then? Or is it still polling?

  2. Anonymous says:

    Raymond,

    my acer travelmate (running xp pro) has its harddrive light on almost all of the time when i’m not working with the machine. [i can see the light, because obviously the laptop is not located under my desk. :) ]

    i just need to stop typing and wait for a few seconds and it’ll turn on. soon as i do something (like opening taskman to find out what process is doing that) the light stops. obviously, taskmanager never shows any activity … :)

    my other acer shows the same behaviour…

    maybe this is the index service, but thats just a guess … i never really took the time to find out what is causing this.

    anyhow: something in xp is making the hd lamp blink, at least on two acer laptops :)

    WM_CHEERS

    thomas woelfer

  3. Anonymous says:

    On XP and 2000 (or even the rest of the NT line), it’s two things:

    1. It could be IndexServer indexing your drive’s content.

    2. It’s the VMM walking through your pagefile taking dead pages and writing zeroes to them for security and perf. reasons.

  4. Anonymous says:

    Thomas,

    did you checked for any bios updates for your acer laptop ? I had a acer laptop some time ago and hadnt this problem.

    Sonu

  5. Anonymous says:

    Observant users will have noted that it’s Morse Code.

    I read it as "Send help… entombed Redmond basement… nothing to eat but stale Dove bars… fading fast… For the love of God, Montressor…"

  6. Anonymous says:

    I hated that feature. I had a very primitive CDROM drive (I think it was a 1/2 speed. No kidding.), and not only did the case light go on, but the CD light would go on, much as it would if I had left a disc in there.

    But most hard drives of that era had two pins so you could attach the hard drive light directly to the drive, which I did. Worked great until I got a second hard drive, and had to use the turbo light. The third drive I put games on, so I didn’t care.

  7. Anonymous says:

    On XP and 2000 (or even the rest of the NT line), it’s two things

    oh good, because I’ve been observing this for a while, and it’s getting me really paranoid. kept thinking that maybe I have spyware on my machine stealing stuff. now I just need to figure out why my cable modem activity light kept on blinking. my current theory, either some spyware or maybe a worm. :)

  8. Anonymous says:

    I think the system heartbeat causes blinks too (writing a timecode or something to disk/registry to calculate the uptime past a crash).

  9. Anonymous says:

    System heartbeat isn’t enabled on client machines, since it screws up power management by spinning up the hard drive.

  10. Anonymous says:

    now I just need to figure out why my cable

    > modem activity light kept on blinking. my

    > current theory, either some spyware or maybe

    > a worm. :)

    … or perhaps inbound traffic?

    Cable modems are a two-way street, you know…

  11. Anonymous says:

    On any NT-based system, it could also be the working-set trimmer writing dirty pages out to the hard disk, either to the swap file or to the mapped file if it’s a memory-mapped file (read-only and non-written pages are simply discarded).

    XP also performs some idle-time disk optimisation using the Prefetch information, IIRC.

    As far as I’m aware, the ‘disk’ light has always been connected to the disk controller in most machines. Few hard disks I’m aware of offer a separate HDD LED connector. We have some IDE removable-drive caddies at work which do show the activity on the actual disk, but that’s rare.

  12. Anonymous says:

    How come the add/remove programs dialog in windows 2000 makes my hd light go nuts (I’m talking about after the annoyingly slow rendering phase where it decides to pause the scrollbar a few times)?

  13. Anonymous says:

    Mike writes: "Few hard disks I’m aware of offer a separate HDD LED connector.".

    Really? I’m pretty sure all of mine do. It’s never labelled, but often there are two pins on the front end of the drive.

    But it might depend on who you buy drives from. It’s also possible they’ve dropped it in recent years; the last HD I bought was just before ATA/100.

  14. Anonymous says:

    asdf: go out to http://www.sysinternals.com/ and grab FileMon. Windows is querying for the uninstaller, looking at access times, and basically just scanning the entire drive. (not really, but it sure looks that way).

  15. Anonymous says:

    RE: Disc Activity:

    On XP you could also have System Restore making a backup of your configuration.

    Or if your organisation runs SMS or some other auditing tool it might be scanning your system for junk (always fun when you’re running on batteries, you’re down to the last few minutes, and the SMS Agent decides to run an inventory of your system…NOT!)

  16. Anonymous says:

    Why are users worried about harddrive activity, or RAM useage. The more RAM you use and the more activity you get simply means that you use your equipment. Of course I’d like my laptops harddrive to spin down from time to time to save the batteries but on my stationary I couldn’t care less.

  17. Anonymous says:

    My problem with W2K and harddisk activity is not during operation but during the boot phase. I have one machine with four IDE harddrives. When W2K boots on that machine it will spend not seconds but minutes maltreating the harddrives. I have no idea what it does but it sounds real nasty. Sounds more like a IDE drive stress test than normal disk operation. And it prolongs the boot process beyond acceptable levels. So far I wasn’t able to figure out what causes this.

  18. Anonymous says:

    Florian wrote:

    > When W2K boots on that machine it will spend

    > not seconds but minutes maltreating the

    > harddrives. I have no idea what it does but

    > it sounds real nasty.

    Then log the boot process to a file and find out what it’s doing.

  19. Anonymous says:

    Yup, already did that. I also logged it to the screen, doing away with the W2K boot animation screen. No clues. (At least none for me).

  20. Anonymous says:

    It is a traking program embeded in most Mircrosoft operating systems. It’s main purpose is to (try to) keep track of the number of pirated copies of their OS out there. Big brother is watching.

  21. Anonymous says:

    I’m looking for a small utility or app that shows hard disk activity (IOW the light or R/W activity in a status bar or sys tray. Does anyone know if something like this exists?

    Please advise.

  22. Anonymous says:

    Commenting on this article has been closed.

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