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My friend recently asked me why the hard drive on his Windows 7 (x64) computer would start to rev up and make loud noises when he was doing seemingly innocuous tasks like browsing the web, but was often silent when performing more intensive tasks like playing video games.

I told him that it was probably the operating system's cache loading new files from the hard drive in advance, before they're needed.

However, I wonder if I was right. Would hard drive whirring at inexplicable times really be the result of the cache, or is it something else entirely?

  • What is the OS? – Ryakna Oct 29 '14 at 8:37
  • Updated. Windows 7, x64 – Strill Oct 29 '14 at 8:38
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If the system is clean, then the search indexing is probably responsible. When some resources are idle, it kicks in.

To troubleshoot, disable the Windows Search service and restart. If the drive is quieter, then there's your answer.

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As sawdust mentioned, the OS disk cache does not randomly decide to read things in on the off chance you may need them in the future. Your understanding of "intensive tasks" is also flawed. A video game may tax your ram, gpu, and cpu, but once it has loaded, they generally don't do hardly any disk IO.

  • "the OS disk cache does not randomly decide to read things in on the off chance you may need them in the future" What about SuperFetch? en.wikipedia.org/wiki/Windows_Vista_I/O_technologies#SuperFetch – ChrisInEdmonton Oct 29 '14 at 19:33
  • @ChrisInEdmonton, that's not random; it is at boot time or when you open a program. In both cases the system knows what it will need to boot or open the program because it is going to be the same as it was last time. – psusi Oct 29 '14 at 23:47
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You are probably right, the browser's cache stores pages, images and other resources when you load web pages. Disk activity could also be caused by other processes, freeing up memory by storing it to disk, etc.

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Would hard drive whirring at inexplicable times really be the result of the cache,

No.
A modern PC has several caches in various subsystems, so simply mentioning "cache" without further qualifying what you mean (e.g. disk drive, processor, or OS) is ambiguous.

More often the OS cache will have data that was written out to disk or read-ahead of already open files, rather than guessing what "new files in advance" might be read.

or is it something else entirely?

Browsing the web can cause can cause disk access for loading fonts, but most likely the disk activity is related to recording the browsing history, authenticating and updating cookies & certificates, and writing a copy of downloaded web content (e.g. Firefox maintains a directory named "cache", and Internet Explorer also has a folder for saving "webpages, images and media" content named "Temporary Internet Files").

Web browsing today is a lot more I/O and computational intensive than back in the day when WinXP was introduced. The minimum system RAM requirement for WinXP was originally only 64MB. Back then you didn't have an anti-virus or anti-malware program running concurrently to protect your system. There wasn't animated graphics (e.g. Adobe Flash) or Java scripts or other add-on & plug-in programs running in frames within the browser window. All of these additional programs are executing concurrently with the modern web browser, and can cause additional disk activity.

  • I did specify which cache. The operating system's. – Strill Oct 29 '14 at 9:12
  • Okay, you did one time. But that's not in the title nor the line I quoted. More often the OS cache will have data that was written out to disk or read-ahead of open files, rather than guessing what "new files in advance" might be read. – sawdust Oct 29 '14 at 9:18
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    Also, code faults in as needed. If the disk wasn't spinning and the browser just happened to hit some code that hadn't run before (say, handling a timeout or other rare condition) the code that handles that may need to be read in from disk, which would require spinning it up. – David Schwartz Oct 29 '14 at 9:21
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One thing worth mentioning is that the hard drive controller (the actual circuit board inside the drive) has to check on the physical position of the cylinders as the temperature of the drive changes. This is sometimes what the drive is doing when absolutely nothing else is being done by the user. As others have mentioned, there is also delayed writes and indexing going on by the OS too.

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