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HTG Explains: Why Do Hard Drives Show the Wrong Capacity in Windows?

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If you’ve ever purchased a computer with a hard disk capacity of 500 GB and opened Windows Explorer only to find that its capacity looked more like 440 GB, you may be wondering where all those gigabytes went.

There are several reasons Windows could display the wrong amount of available space, from invisible shadow files, formatting overhead, and hidden recovery partitions to misleading (though technically accurate) storage capacities advertised by hard drive manufacturers.

Image Credit: Norlando Pobre

Why Your Hard Drive Shows Less Space Than Advertised

If you’ve paid attention to hard drives, USB flash drives, and other storage devices, you may have noticed that they always have less space than promised once they’re formatted. The reason for this difference lies in the way hard drive manufacturers advertise their devices, versus the way Windows computers actually use the storage devices. There’s also some overhead required when Windows formats your drive, for the file system and boot data, though in comparison to today’s large hard drives, it’s not a lot.

To a hard disk manufacturer, one KB is 1000 bytes, one MB is 1000 KB, and one GB is 1000 MB. Essentially, if a hard disk is advertised as 500GB, it contains 500 * 1000 * 1000 * 1000 = 500,000,000,000 bytes of space. The hard disk manufacturer thus advertises the disk as a 500 GB hard disk.

However, manufacturers of RAM don’t sell it in even groups of 1000 – they use groups of 1024. When you’re buying memory, a KB is 1024 bytes, a MB is 1024 KB, and a GB is 1024 MB. To work back from the 500,000,000,000 bytes above:

500,000,000,000 / (1024*1024*1024) = 465.66 GB

Keep in mind that the hard drive manufacturers are using the accurate description of the terms–the prefix giga, for instance, means a power of 1000, whereas the correct term for powers of 1024 is gibibyte, though it isn’t often used. Unfortunately, Windows has always calculated hard drives as powers of 1024 while hard drive manufacturers use powers of 1000.

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That’s a difference of nearly 35 GB over what the average buyer would be led to believe a hard drive contains. If hard disks were advertised in terms of the amount of space they actually contained when you connected them to your Windows computer, a 1 TB hard drive would be labeled a 931 GB hard drive instead.

Alternatively, Windows could update their UI to use the correct definition of gigabyte–other operating systems, like OS X, have already changed their representation to correctly state the right amount of space.

Why Your Computer Shows the Wrong Amount of Free Space

You’ll probably notice something odd about the amount of free space your hard drive contains, if you look closely. If you right-click your C: drive in Windows, you’ll see a certain amount of space referred to as “Used Space” – in the screenshot below, the hard disk contains 279 GB of files.

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However, if you select all the files on your C: drive (including hidden files and Windows system files), right-click them, and select Properties, you’ll notice something odd. The amount of space used by files doesn’t match up with the amount of used space on your hard drive. Here, we have 272 GB worth of files on our C: drive – but Windows is using 279 GB of space. That’s a difference of 7 GB or so – where did all those GBs go?

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It turns out that certain types of files don’t appear in Windows Explorer. Files in Windows’ aptly named “shadow storage,” also known as “shadow copies,” don’t appear here. The shadow storage contains System Restore points and previous versions of files for the Previous Versions feature in Windows Explorer.

To view the exact amount of storage used by shadow files on every hard drive attached to your system, you can run the command below. You’ll need to run it as Administrator – to open a Command Prompt window as Administrator, search for Command Prompt in the Start menu, right-click the Command Prompt shortcut, and select Run as administrator.

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Run the following command in the Command Prompt window:

vssadmin list shadowstorage

As we can see in the command below, about 9 GB of space is used in our hard drive by the Windows Shadow Copy Storage. The difference above looked more like 7 GB, but that can be explained by rounding.

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To adjust the amount of hard drive space used by the shadow copy service (System Restore and Previous Versions of files), follow this guide: Make System Restore Use Less Drive Space in Windows 7

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Other Partitions

Laptops and desktop computers often come with several partitions, including a hidden recovery partition. If you’re wondering why a new computer has less free space than its hard drive specifications would lead you to believe, there’s a good chance some of that is taken up by a separate recovery partition.

To check for partitions, use the Disk Management application included with Windows. Click Start, type partitions, and select the Create and format hard disk partitions shortcut to open it.

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The hard drive should report its correct size in the Disk Management window. As we can see in the screenshot below, nearly 11 GB of the hard drive’s space is reserved for a hidden recovery partition. This is fairly typical of laptops and other computers you don’t build yourself.

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Each of these factors can take a bite out of your available hard drive space, leaving you with less space than expected for your own use.

Chris Hoffman is a technology writer and all-around computer geek. He's as at home using the Linux terminal as he is digging into the Windows registry. Connect with him on Google+.

  • Published 08/30/12

Comments (47)

  1. Murali

    Very good explanation.

  2. Murphy

    The HDD producers for my opinion uses these marketing tricks to sell a smaller products. As historically computers were not having HDD, but some other media like paper and magnetic tapes, floppy disks, etc. For the first two I never saw the capacity in kB written on them. For the floppy disks there were more accurate capacity descriptions (I remember 1,44 MB was a true 1440kB when formatted). Some examples of the floppy disks capacities are in wikipedia:

    http://en.wikipedia.org/wiki/Floppy#Sizes.2C_performance_and_capacity

    But then why HDD producers start to use the SI (metric) units instead of the binary interpretations as for sure there will be bytes stored and not other things? For me it looks like the unfair market practices:

    http://en.wikipedia.org/wiki/Byte#Unit_multiples

  3. neumac

    In german speaking countries (where I hail from), us geeks consider GiB (2^10 = 1024) the correct term to define hard drive sizes vs. GB (10^3 = 1000), which nowaday mostly exists to help hard drive makers’ claims of capacity appear more substancial…
    To me GiB seems more logical, as it evolved from powers of 2 to describe amounts in a binary system (which has two states – thus powers of 2). Powers of 10 belong in decimal systems. ;)

  4. r

    One security issue with all this occurs when you decide to protect one of your documents.
    First, you create an encrypted copy of the doc. Then you “secure-delete” the original doc.
    If the original file was stored on a volume protected by the VSC service & it was there when a restore point was created, the original file will be retrievable using “previous versions”. All you need to do is right-click the containing folder, click “restore previous versions”, open a snapshot, and you’ll see the original file. The reason is that before the file’s blocks get overwritten, VSC saved them to the shadow copy safely stored on a hidden volume.

  5. Paul

    All that matters is the number of bytes. I bought a 2 TB drive, and was shocked (at first) to see Windows showing it as only 1.81 TB. Thought I’d been ripped off. But the actual number of byte space on the drive is 2,000,395,694,080 bytes — that is, 2 TB. So, no problemo.

  6. mitilini

    Always great tutorials by you guys.That’s why we visit you every so often.

  7. AndyR

    I tried that command to found out the size of the shadow storage, but it came back with ‘No items found that satisfy that query’. Was going on there then?

  8. r

    @AndyR
    if you recently deleted your restore points then Disk Mgt. hasn’t caught up yet. Reboot & try again.
    –difficult to really know unless one were to read your Event Viewer in Disk Mgt.

  9. keltari

    Its not just hard drive vendors that do this, even large SAN vendors do the same. We bought a several petabyte array from Hitachi and came up short on the storage. However, when threatening to return the product and go with a competitor, they gave us the remaining storage for free. They didnt want to lose a several million dollar sale for a handful of hard drives.

  10. SatoMew

    That’s why Windows should change to using IEC binary units (1 KiB (kibibyte) = 2^10 bytes = 1,024 bytes) instead of keep using SI binary units (1 KB (kilobyte) = 10^3 bytes = 1,000 bytes). It’d help in solving this problem by using the proper units for the storage space.

  11. Makky

    That’s a nice enlightenment.u guys are doing a nic job.

  12. bedlamb

    @AndyR

    Another possibility is that you’ve turned off the nearly useless ‘system restore’ feature in windows.

  13. Chronno S. Trigger

    @SatoMew

    Windows is using binary units. That’s why this confusion comes up. Windows measures in 1024 chunks where as hard drive manufacturers measure in 1000 chunks.

    Now, since everything else in a computer is based off of Binary, I think hard drive manufacturers should be the ones to change. We’ve been measuring things in powers of 2 for way, way longer then they have been around.

  14. nwidesigns

    This is just one problem of why there needs to be standards and all manufactures (both hardware and software) follow the same rules. We can also see this abuse in the bandwidth industry. We hate government but this is an area where it is obvious the industry cannot manage itself and stay honest!

  15. SatoMew

    @Chronno S. Trigger, I was talking about different units, I didn’t say Windows does not use binary units. Ever heard of kibibyte (which I mentioned in my previous comment)? Read more on Wikipedia: https://en.wikipedia.org/wiki/Kibibyte

  16. r

    @nwidesigns

    It’s wishful thinking but one of the main reasons why the the entire PC market has been so affordable, when compared to Apple’s, is due to the fact that standards & practices have been left more or less open in many areas of software & hardware. It takes a while, but developers slowly migrate to what serves them the best & users have some choice. “Honest Industry”..well, that’s another argument entirely.

  17. Siosilvar

    The whole problem would disappear if Windows added the extra “i” in between the “G” and “B” in GiB, like Linux does (I’m not familiar enough with Macs to know how they display capacity). Alternately, they could use the more-understandable multiples of 1000 and keep the GB label.

  18. SatoMew

    @Siosilvar, it’s not merely an extra I. It’s kibibyte (KiB), mebibyte (MiB), gibibyte (GiB), tebibyte (TiB), etc., which are IEC units (binary prefixes based on powers of 1,024) vs. kilobyte (KB), megabyte (MB), gigabyte (GB), terabyte (TB), etc., which are based on the SI units (binary prefixes based on powers of 1,000).

  19. nwidesigns

    @r you are so right and I do everything I can to engage my customers and educate them about things such as this. Really as long as everyone is aware of the underhanded tactics that goes on the less the markets will be to use them to their benefit!

  20. AR

    Thanks, that explain alot

  21. jhay

    .yay^^ thanks for the info!….

  22. vipin kumar

    you guys are doing great job.

  23. Ron007

    It is time for MS “to step up and do the right thing”. Add a new “regional” setting to select binary or decimal file size display.

    Until recently, the difference wasn’t significant but as the “powers” increase, so does the gap
    Symbol Prefix SI Meaning Binary meaning Size difference
    K kilo 103 = 10001 210 = 10241 2.40%
    M mega106 = 10002 220 = 10242 4.86%
    G giga 109 = 10003 230 = 10243 7.37%
    T tera 1012 = 10004 240 = 10244 9.95%
    P peta 1015 = 10005 250 = 10245 12.59%
    E exa 1018 = 10006 260 = 10246 15.29%
    Z zetta 1021 = 10007 270 = 10247 18.06%
    Y yotta 1024 = 10008 280 = 10248 20.89%

    Multiples of bytes
    SI decimal prefixes Binary
    usage IEC binary prefixes
    Name
    (Symbol) Value Name
    (Symbol) Value
    kilobyte (kB) 103 210 kibibyte (KiB) 210
    megabyte (MB) 106 220 mebibyte (MiB) 220
    gigabyte (GB) 109 230 gibibyte (GiB) 230
    terabyte (TB) 1012 240 tebibyte (TiB) 240
    petabyte (PB) 1015 250 pebibyte (PiB) 250
    exabyte (EB) 1018 260 exbibyte (EiB) 260
    zettabyte (ZB) 1021 270 zebibyte (ZiB) 270
    yottabyte (YB) 1024 280 yobibyte (YiB) 280
    See also: Multiples of bits · Orders of magnitude of data

  24. Ron007

    Didn’t mean to hit enter …

    There is one more type of “un-reported” space on the HD. When the first HD’s came out, they were MUCH less reliable than now. Small pieces of the HD would become defective on a regular basis. So to compensate, the manufacturers ship the drive with some unreported space that can be allocated to replace the “missing’ bits That way the HD continues to report the same size, until it completely fail.

  25. Wayne in Indy

    Very nice article. One other small quark of storage is block and cluster size. Files most often do not completely fill the last block of the file, so on average there will be 1/2 a block times the number of files wasted. So for 500,000 files, if your block size is 1024, you will lose about 1/4 Gig. No big deal today, but I can remember when a 256 megabyte drive was a huge disk.

  26. clamo

    no the real reason y hdd capacities are different then what the manufactures say is because of Microsoft.

    the windows OS is not capable of fully detecting the hdd’s actual space hence y you loos a bit of it. not to mention the different partitions that are used. and this is do to the fact that MicroCRAP does not believe in 1000bytes= a megabyte. also NTFS partitions use more space than FAT16 or 32. but FAT 16 and 32 don’t allow you to fully use the amount of space that’s windows detects ether, but NTFS does.

    if you install a 2tb hdd in linux you will see that the hdd will use closer to the amount of actual space your drive has do to the fact that UNIX based OS’s see’s 1000bytes as 1 megabyte. and UNIX systems don’t use large partitions like windows does.

    O and btw comparing ram megabytes to hdd’s is not a good way to explain this as ram does not use partitions, nor is it the same tech. ram chips are not hdd platters. “ssd’s are comepleatley different to”

  27. Siosilvar

    @SatoMew

    No, it really is just an extra ‘i’. As it stands, Windows displays sizes in GiB but uses the incorrect “GB” unit. The solution is to either fix the displayed size to match the unit or fix the unit to match the display size.

  28. Siosilvar

    @clamo
    Please stop deliberately spreading misinformation. Windows is perfectly capable of detecting the whole HDD’s space, NTFS has a smaller footprint than FAT does on bigger drives (e.g. an HDD), I’ve recently looked at a disk in Ubuntu that displayed its size in MiB, and the fact that RAM isn’t the same technology is irrelevant to the discussion.

  29. Raging Piton

    When I got my new laptop it had exactly 465 GB instead of 500 GB just like you said!

    I’m so dumb that I thought the remaining space was preserved for over provisioning. Just imagine me comparing SSD technology to HDD just to calm myself.

  30. Suvrojit

    This is an odd request. But can you tell me in the first screenshot which view & sort… settings you have selected? Because it shows the drives in much bigger icon with details too & the font is looking cool too….

  31. Leisa

    @ Paul, you are misleading yourself if you think you got what you paid for.
    2,000,395,694,080 bytes is 2 TB only to drive manufacturers, but it is NOT really 2 TB.
    2 TB is actually 2 * 1024 * 1024 * 1024 * 1024 or 2,199,023,255,552 and you didn’t get that, so you ARE being ripped off.

  32. keshav37a

    excellent article

  33. kickass

    @Leisa, the fact of the matter is that he has recieved over a trillion bytes which in logic means that he has more than 2TB According to the manufacturer, so he can’t really complain.

  34. Bailey

    Great article but am I the only one that noticed that the Used space and Free space don’t add up to 412 GB??? LOL

  35. SamCal

    That’s an interesting way to attempt to explain it to the masses. But Hard Disk Drive (HDD) capacity has more to do with physics. HDD technology predates Apple, Microsoft, and most other modern operating systems. Originally HDDs were extremely expensive, HUGE, and only available to large corporations, research institutions, and the military. (I’ve worked with early 10MB HDDs the size of a sofa.)

    HDD makers must state the devices’ ability to retain individual ‘bits’ of data – but they do not have much control over the eventual employment of that capacity, e.g., file system, # tracks, # sectors, data word size, checksum requirements, redundancy bits for error correction, etc. [Unless they are making a proprietary design or limiting the product to specific applications.] It is extremely unlikely that two DIFFERENT operating systems would ever be able to obtain exactly the same end-user capacity as reported by the different file systems. That doesn’t mean you were cheated.

    Think of it this way: when you purchase a gallon of gasoline you are buying the producer’s certification that 1 gallon of fuel will produce “X’ amount of energy (under some stated conditions) to be used as you desire. The OEM has no control over vehicle (car, truck, lawn mower, chain saw); conditions (hot, cold, high altitude); driver (grandma, racer, etc). One user may get 10 mpg while another might get 35 mpg.

    It’s a very similar issue with HDDs. There is a minimum capacity of “bits” of data the OEMs certifies the device’s technology is capable of reliably delivering (at defined error rates and other conditions). If you could load a HDD to capacity with all the bits it could possibly store and then counted ALL those “bits” in base 10 units as in 1, 2, 3, 4, 5, 6, 7.. 39, 40… 127, 128… 1,024… then you will eventually reach the OEM ‘certified’ capacity.

    In most cases, however, the OEM has no control over the end application. The HDD on the shelf at Best Buy may go into a Windows, Mac, Linux, Xbox, etc. If one end-user uses Windows and another uses Linux and another uses CP/M and another uses a proprietary military file scheme, then the end-users will see a different ‘count’ consistent with THAT file system’s rules.

    Now that HDDs are a commodity it can be confusing for the general public without technical background. I think OEMs have done a reasonable job in labeling the devices and boxes. But the old bits vs bytes is only part of the confusion, IMHO.

    Another (admittedly weak) analogy: You go to the bakery and buy a 5 lb cake. Later you slice it into 2, 3, 4, 8, 12 or 16 pieces but in the end you still have 5 lbs of cake. (Minus the waste that sticks to the knife, which is a lot like the file system ‘overhead’ discussed in other posts.) The bakery sells the 5 lb cake and leaves it up to the end-users to slice according to their need/preference. But would you take that cake back to the bakery and tell the baker “Hey, I just sliced this 5 lb cake into 128 pieces but when I weighed all the individual pieces and added the weights together, it came to only 4.5 lbs?? You cheated me!!”

    Personally, I’ve never had an issue with the HDD capacity specs because I have been working with them a long time and understand the above. My first personal HDD was a 10MB that cost $995 in 1980!!

    Now, who can explain why I never EVER get 7 years of service out of a CFL bulb?? It says so right on the box !! ;-)

  36. clamo

    @Siosilvar: please get a real education. I have been doing this for years.

  37. clamo

    @Siosilvar: “NTFS has a smaller footprint than FAT does on bigger drives” ya sure but its still not as small as UNIX based partitions. hence its Microsoft that’s caused this problem. NTFS is a Microsoft windows partition. https://en.wikipedia.org/wiki/NTFS
    BTW like I said get your self a real education.

  38. EW

    As far as I’m aware, the 1024 base is the original and predates the use of the 1000 base in the computer industry by at least a few years. Since 1024 is a binary multiple, it also just makes more sense in binary systems. Storage manufacturers were the first and for a while only real users of the metric base, presumably since it conveniently made their products look like they had more capacity than they actually did (see: http://www.swtpc.com/mholley/SA400/SA400_Datasheet.pdf, advertised as 109.4 KB with an actual byte count of 35 x 3125 = 109,375).

    IMHO, that’s a pretty shady tactic and I applaud Windows for not yielding and letting them be the victors on what KB, MB, GB, TB, etc. means. Also, I admit I’m a bit biased against the IEC terms. KiB, MiB, GiB, TiB, etc. all look and sound ridiculous to me. Yes, the original terms use metric prefixes, but the byte part of the term should be enough to signify the 1024 base. I would have liked that to be made some sort of standard the storage manufacturers would have to conform to, but with the IEC’s decision, it looks like that may never happen.

    (And no, I’m not some old computer guy set in his ways and grumbling about changes to things I’m used to. I’m 24. The issue doesn’t make working with data any harder, but its existence is still a slight annoyance.)

  39. Roland

    2 terra byte data are 2 199 023 255 552 bytes data, nothing less or more. So it is a number-trick (like the author wrote, a marketing trick) to sell you smaller disks for same price. So I may call this cheating on us customers. :(

  40. Mesum

    I am really flabbergasted with this definition. I hope and pray you will definitely continue to send such valuable know-how and make them public for the betterment of people like us.

    Thanks !!!

  41. spike

    @SamCal: It depends on where you get your bulbs from. Good ones last a lot longer :) Good post, BTW.

    @clamo: If you cannot even spell simple words, nobody will ever believe you.

  42. Wayne Riker

    Good article.
    Would like to see a follow article up for ADS (Alternate Data Stream) metafile on NTFS partions. ADS can use up ‘invisible’ space as well. Windows will not report the disk space used. For example I could create a small Notepad file of a 500 bytes, attach a 1 gigabyte photo as an ADS. Windows will only report the the original 500 bytes, leaving you to wonder why the file will not fit onto an NTFS thumbdrive. You can put it on an FAT thumbdrive as the ADS will be stripped during the move.

  43. Skywagon

    Enjoyed the article. Just wish that it had gone a little further or maybe my interest is for another article. I have a Vista laptop with a 160Gb drive. I cloned the drive using a 250Gb drive and ISO for an exact image. The resultant clone worked as expected. However, when, I checked its volume details it came back reporting that it was a 160Gb drive. Obviously, it copied ‘every detail” from the 160Gb drive. I have not found a way to correct this volume size flaw….hints.
    Thanks…..

  44. Martin Nowers

    Thanks for v informative article. I hope you won’t mind me putting a related question namely, how to make Windows (Win7 X64) show the size of folders, and show the size of both folders and files as Mb not bytes. This would save a lot of column width, and be less fatiguing than working out size in Mb from a large number of bytes. I hope the result would show in PowerDesk 8.5

    I wish Microsoft would see this problem through the eyes of it’s customers!

    Kind Regards, Martin Nowers

  45. kishore

    I thought the hidden spaces were used for file allocation table to store information about the files and folders. If the 500gb hdd gives you 465.66 GB and this 465.66 is fully occupy-able were are the information about files are stored ……

  46. Naeem Qureshi

    very useful information. Actually i still have wondered but this information was required during RAID configuration and i came to know. Thanks a lot. keep going

  47. shuffles

    hi, i found the article helpful although my problem seems to be of a somewhat larger scale.
    I am running a 500gb external hard drive. files on it total 81gb. capacity shown is 465gb. used space 296gb and free space 181gb
    i cannot find the command prompt. have i got a bigger problem here? any tips please would be greatly appreciated.
    thanks

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