The light blinks faintly about once a second.

It is slowly driving me insane.

How do I find out which program is causing this, so I can disable it?

Acer 5274 laptop/core i3
Windows 7 Home Premium
Hitachi HTS545050B9A300 hard drive

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    It has something to do with the black helicopter hovering overhead. – Daniel R Hicks Dec 2 '13 at 22:52

It may be the operating system polling the optical drive to see if you have inserted anything - the hard disk and optical disk share common circuitry and so the LED may apply to both. You could try turning off autoinsert notification (Device Manager - look at the properties of the optical drive) and autorun.

A bit more info here: .../cdtTipAutoRun.htm (broken, replacement: http://web.archive.org/web/20100527203945/http://www.base40.com/cdtTipAutoRun.htm)

  • Healthy debate on the subject for the inquisitive: social.technet.microsoft.com/Forums/fi-FI/w7itprohardware/… – Linker3000 Jan 6 '11 at 1:24
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    it was in fact the cd-rom. i disabled the cd-rom device in device manager and the blinking went away. i would still like to turn off that light, but it's less of a concern now that i know the hdd is not getting thrashed. thanks – Neil McGuigan Jan 6 '11 at 2:36
  • @Linker3000 I wouldn't count that debate as "healthy", maybe you meant "heated"? :) It was really funny to see that, people think computers work the same as 15 years ago! So much have changed... Funnier was the guy arguing that CD-ROM is not the reason for the blinking because the CD drive has its own led below the tray! I don't know if I laugh or if I weep at that thread.. – NothingsImpossible Nov 30 '13 at 12:51

If you want to see what is going on, on your system, there is a cool tool from sysinternals(they make all the cool tools) called processmon It will tell you literally everything that is going on. You may be shocked to see how much stuff is active when your not.

I'm not saying you will be able to stop your light from blinking every once in a while, but at least you can see what is going on.

  • @thepurplepixel :D – Jeff F. Jan 5 '11 at 21:47
  • another +1 for sysinternals, but Windows 7 does have a built-in application. start->type "resource"->select "resource monitor" Check disk reads. My guess is that it is the indexing service. – horatio Jan 5 '11 at 21:53

The real culprit of HDD LED blinking on my Acer notebook was the service internally named BrcmCardReader with the long name Broadcom Card Reader Service. As soon as I've stopped the service the blinking stopped too. And of course I didn't have to disable the CD-ROM or cover the LED with the tape to achieve this. Contrary to what's written in the other posts here, the operating system itself isn't so badly written to poll anything. But this service written by Broadcom is another story.

I've first tried to figure out what causes the blinks only to find that it was something like wbem wmiprvse.exe that did things like IRP_MJ_QUERY_INFORMATION and IRP_MJ_QUERY_VOLUME_INFORMATION for every drive. As I knew that wmiprvse is actually a WMI execution component written by Microsoft I even tried using Event Log to trace the WMI activity, as documented on MSDN. It wasn't useful, I was able to observe only

ProviderInfo for GroupOperationId = 101; Operation = Provider::CreateInstanceEnum - CIMWin32 : Win32_LogicalDisk; HostID = 2368; ProviderName = CIMWin32; ProviderGuid = {d63a5850-8f16-11cf-9f47-00aa00bf345c}; Path = %systemroot%\system32\wbem\cimwin32.dll

Microsoft obviously does poor job in this trace: the CIMWin32, the host id, the provider guid and the path all point to the binary executing the WMI, not to the program making WMI queries. So at that moment I wasn't able to discover that Broadcom Card Reader Service does it as nothing logged pointed to it, that's why I'm quoting all this in order to ease the pain for anybody who puts these items in the search machine. This inability to see who actually commands the activity is also the explanation why some people here claim that "it's an operating system:" whoever stops at this point doesn't see anything else. But I knew that wmiprvse isn't doing it on itself, I knew there must be some other process commanding.

So finally one day after I've made an image backup of my whole system, I started with the brute force approach, turning off the things one by one, until the blinking stopped. So now I'm sure. It is the Broadcom Card Reader Service. And as I'm actually a programmer, I've even inspected the strings inside of c:\Program Files\Broadcom\MemoryCard\BrcmCardReader.exe and I've found what it exactly does, as soon as it's turned on:

SELECT * FROM __InstanceDeletionEvent WITHIN 1 WHERE TargetInstance ISA 'Win32_LogicalDisk'

SELECT * FROM __InstanceCreationEvent WITHIN 0.1 WHERE TargetInstance ISA 'Win32_LogicalDisk'

Since the blinking happens so regularly, it's obvious that it is polling continuously. That is unbelievably bad programming of the service. Observe the WITHIN clause in the queries. Specifically, Microsoft documents how such constructs behave in the WMI:


Note that the WITHIN clause specifies the polling interval for intrinsic event classes. Because the class being monitored does not have a corresponding event provider, the WMI polling mechanism is used to periodically check if an intrinsic event has occurred for the particular class. This polling interval is specified by the WITHIN keyword and measured in seconds.

So I now know that Broadcom service programmers decided to poll for the __InstanceDeletionEvent of every logical disk every second and for __InstanceCreationEvent even 10 times per second! And they manage to involve COM, separate processes and do this over WMI/wmiprvse in a way that it's not observable (at least I haven't found out) that their service is doing this!

Bad, amazingly bad programming.

And there's proper solution for services and applications: RegisterDeviceNotification. A real notification (that is, quiet when there's nothing new happening) can be received by services via the SERVICE_CONTROL_DEVICEEVENT event. See for example:


After knowing all this, the search for Broadcom Card Reader Service actually returns a few posts of people who discovered it earlier: on community.acer.com (I'm quoting the posts for which I haven't found permalinks):

"Vladan Re: Aspire 5750Z card reader driver,Win 8 11-29-2012 06:29 AM

Just discovered that Broadcom Card Reader Service is causing hdd led to blink multiple times per second, all the time. Stopping and setting this service to manual or even disabled fix the blinking problem with no impact to card reader functionality."

on the bleepingcomputer.com:

"Cheesenbranston Posted 28 May 2013 - 04:47 AM

I've had a similar issue since installing Win8 pro x64 as a fresh install i.e. not an upgrade. In Task Manager although disk throughput didn't seem particularly high usage was constantly at 100%. I believe I've identified the issue as being the Broadcom Card Reader service."

and on Amazon.co.uk, a review by S. J. Harvey on 1 Feb 2013:


The one thing that REALLY bugged me (note the past tense) is that the drive light flickered constantly. It wasn't HDD activity and after a couple of hours I traced the culprit. It was the Broadcom Card-Reader service.

He further suggests switching the service to manual, on my computer I had to disable it completely though.

So people even reported higher resource usage, apart from just HDD LED blinking.

The final solution: disable the "Broadcom Card Reader Service": in Services go to its properties, stop it and change its startup type to "disabled". The blinking will finally stop. I'd really like to know what's the purpose of it anyway -- what I'm missing by turning it off? Seing how poorly it is programmed, I wouldn't be surprised that the whole purpose of the service is to change some icon when the memory card is inserted! What I'm sure is that misusing the WMI is really bad programming.

  • holy carp. This is a pretty epic answer – Journeyman Geek Dec 3 '13 at 9:43
  • Thanks. I've bought a new notebook and it behaved like it has an army of malwares installed. It really annoyed me. Such service programming should be really put to shame. It is appropriate for some sysadmin maintaining some server in his company but not for the service to be installed on the millions of the notebooks. – acqq Dec 3 '13 at 10:14
  • Welcome to Super User! While this is a great post, please keep in mind that edits should be substantial. Any edit causes the question to be bumped, so please refrain from doing minor corrections—after all there have been 19 revisions on this post already. After 10 revisions you lose any reputation you'd have gained too. Thanks for your understanding. – slhck Dec 4 '13 at 7:54
  • To remain on topic: does anybody have some other version of c:\Program Files\Broadcom\MemoryCard\BrcmCardReader.exe ? Mine reports in file properties version, file date ‎20 ‎August ‎2012, ‏‎17:36:22. It also contains strings MS\ sXD\ \sSD bicms.ico bicxd.ico bicmmc.ico bicsd.ico, and the mentioned ICO files are in the mentioned subfolders, so it seems it really does that polling insanity just to show the different icons! – acqq Dec 4 '13 at 18:47
  • The picture of the icons: i41.tinypic.com/27ziwyx.jpg – acqq Dec 4 '13 at 18:58

Install and run Process Explorer.

Select View menu and then Select Columns. In the Select Columns window, select the Process Performance tab. Tick I/O Reads and I/O Writes. Click OK.

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    Process Monitor seems more useful for file system activity – Neil McGuigan Jan 6 '11 at 2:35

This is normal. A lot of hard drive activity is generated by the Operating System (windows etc... which you can't disable). There will always be hard drive activity by some program or other, it's just the nature of a computer.

If the activity light irritates you then disable it by either covering it with a sticker or find the header on the motherboard that it is connected to and disconnect it. It will be labelled HD LED or something very similar.

  • Cover the HDD light! Gasp – Jeff F. Jan 5 '11 at 20:47
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    That's what I've done for my monitor... the on LED is a bright blue light that is possibly the worst thought out idea I've ever come across... try to use it late at night and you are blinded by it :D – Matthieu Cartier Jan 5 '11 at 21:53
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    nah, your computer should not be accessing the hard drive every second for ever...it was the cd-rom in this case – Neil McGuigan Jan 6 '11 at 2:35
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    @el chief, no it should not, but apparently some software can be poorly behaved. – Bobson Sep 25 '11 at 20:11

This can also be caused by the "Power" service of Windows 7 checking the power management settings. I suspect that is dependent on the vendor of the hardware (some of them don't use Windows 7 built-in A/C state detection and change the default settings themselves so Windows 7 has been configured to poll the registry).


I had the same problem on my Vaio laptop. Disabling the DVD drive (I rarely use it) fixed the blinking. I had the additional concern of excessive writes though because I recently installed a SSD and I understand their lifetimes are typically limited by the number of write/erase cycles.

At the suggestion of someone on Microsoft Technet I downloaded SysInternals and used Process Explorer (procexp) to monitor disk writes (one of the graph icons on top). I also used diskmon to give a very detailed view of writes. I found a lot writes happening when "idle" so...

I used Windows 7's System Configuration (msconfig) to start up in diagnostic mode (very minimal services and start up items) and lo and behold, ALL writing stopped. Nothing worked :-) but no writes. I then used msconfig to enable just the Microsoft stuff and most funtionality I wanted was there. There were also sporadic writes but much less than normal start up. I got back the rest of the functionality I wanted by enabling a few key services and start up items from Intel and Sony.

Per SSD suggestions I also disabled scheduled defrags, most logging and all fetching and indexing using Windows and SSD Tweaker (downloadable tool).

Now I've got no blinking and a lot less writes to the SSD. Start up and shutdown are also faster though they were already fast due to the SSD. I go from power button to useful desktop in about 15s. IE opens at msn.com instantaneously. Full Security Essentials scans went from 3-4h to 30m. I also do java compiles which I don't have measurements on but I subjectively feel had gains similar to virus scans. I'm a happy camper.


My system running Windows 7 does this too because it's polling the optical drive as mentioned in other answers. My fix is to open my DVD drive tray and then close it. After doing that, the blinking stops for some reason. Unfortunately this means I have to remember to do it every time I reboot my computer.


I have had the same BLINKING L.E.D. problem.

Every second, the computer was checking the cd/dvd player for a possible disc presence. So I placed a formatted but blank content DVD disc within the cd/dvd player, and the blinking stopped. If I just left it there, the blinking would not return.

But I searched for a better cure.

The SSD and the CD/DVD player SATA cables were both plugged into the SATA 3 connectors on the mother board. However, there was one SATA 2 connector that was still left unused. So I switched the cd/dvd player from the SATA 3 connector on over to the SATA 2 connector.

Job done. No more blinking, and the CD/DVD player works just fine.

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