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HDG Explains – Swapfile.sys, Hiberfil.sys and
Pagefile.sys in Windows 8
October 9th, 2012 by Aseem Kishore | File in: Featured Posts (http://helpdeskgeek.com/category/featured-posts/), Windows 8
(http://helpdeskgeek.com/category/windows-8/)
In previous versions of Windows, you probably remember the good ol paging file. It’s used to when physical memory becomes
overcommitted and it hold objects that usually have not been accessed in a long time. That is pagefile.sys. Next, we had the
hibernate option in Windows that let you save the kernel and all applications to your hard drive so that you could start your
computer back up faster than doing a full reboot. That is hiberfile.sys.
In Windows 8, things get more complicated. The pagefile.sys is there all the time, but the hiberfil.sys is only there if you have
fast startup enabled in Windows 8. What is fast startup? It basically allows Windows 8 to perform a hybrid shutdown. This is
why Windows 8 boots up so much faster than previous versions of Windows. Check out my previous post that explains what a
hybrid shutdown is in Windows 8 (http://www.online-tech-tips.com/windows-8/perform-a-complete-shutdown-in-windows8/).
In order to use the new hybrid shutdown feature, which is turned on by default, hibernation has to be enabled in Windows 8. If
hibernation is disabled, you won’t have a hiberfil.sys file and you won’t be able to use the fast startup option either. You can
read my post here about enabling hibernation in Windows 8 (http://helpdeskgeek.com/windows-8/turn-on-fast-startupmissing-in-windows-8-power-options/).
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Now the interesting thing is that when you have fast startup enabled (meaning hibernation is enabled), then your hiberfil.sys
will be about 75% of your RAM and the paging file will be around 25%. This is because the hiberfil.sys contains the Windows 8
kernel and device drivers. The paging file is only used if all RAM is exhausted only our system and is used while you’re
actually running Windows. The hiberfil.sys is only used for the boot process.
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If you don’t have hibernation enabled in Windows 8, you’ll see that the paging file is now the same size as the amount of RAM
you have.
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In the above screenshot, I have a Windows 8 machine with 1 GB of RAM and fast startup disabled. Now that we understand
how that works, let’s get down to the new one: swapfile.sys. What the heck is that? Well, it’s basically like the paging file, but
serves different purposes.
One of the main reasons for the swapfile.sys is to suspend and resume Metro apps. So why not just use the paging file instead
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to do that? It’s used because certain types of paging operations can be done more efficiently using this special type of
pagefile.
HDG Guide to Customizing and Organizing the
Here’s a more clear explanation. Windows 8 supports both paging and swapping. Paging will hold items that haven’t been
Windows 8 Start Screen
accessed in a long time whereas swapping holds items that were recently taken out of memory. The items in pagingfile may
(http://helpdeskgeek.com/windows-8/hdg-guide-
not be accessed again for a long time whereas the items in swapfile might be accessed much sooner.
to-customizing-and-organizing-the-windows-8start-screen/)

2. Also, paging is very effective on high-end machines whereas swapping is more effective on low-end tablets and PCs. Each
paging file has different requirements for dynamic growth, space reservation, read/write policies, etc. If you were to have the
same paging file, it would become fragmented very quickly because of the fixed-size pages used in paging and the big
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chunks used in swapping.
As you can see from above, the swapfile.sys is about 256 MB in size. As of now, it’s used for Metro apps because of their
different paging needs as compared to traditional Windows programs. There may be other uses too for it in the future, but
Microsoft has not specified what exactly.
So that’s what those three files do on a Windows 8 system. Note that there are some interesting and annoying things that can
happen. If you have 16 GB of RAM and are using fast startup in Windows 8, that means you’re going to have a 16 GB
hibernation file too! If you’re running Windows 8 on an SSD, that may be taking up a large portion of your disk space.
You can reduce the size of the hibernation file (hiberfil.sys) in Windows 8 by using the following command:
p owe rcfg.e xe /hib e rna te /size 5 0
This will reduce the size of the hibernation file to 50% of RAM rather than 100%. Note that you cannot lower it any more than
50%. However, if you have a large amount of RAM like 16GB or something like that, you can save yourself 8 GB of space.
The other thing is that you don’t need to worry about the hibernation file becoming too large like in previous versions of
Windows. Earlier the hibernation file stored the kernel, device drivers and all application data. Now that there is no application
data, the size of the file stays pretty constant, so if you have a lot of RAM, you probably don’t need a hibernation file that is so
large anyway.
Hopefully, that gives you a clearer understanding of how the pagefile.sys, hiberfil.sys and swapfile.sys files work on Windows
8. If you have any questions, feel free to post a comment. Enjoy!
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ASE E M KISHOR E
Founder of Help Desk Geek and managing editor.
He began blogging in 2007 and quit his job in
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ABOUT H ELP DESK GEEK
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Welcome to Help Desk Geek- a blog full of help desk tips for
IT Professionals. My name is Aseem Kishore and I work as a
Systems Analyst in Dallas, TX. I graduated from Emory
University in Atlanta, GA in 2002 with a degree in Computer
Science and Mathematics.
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