Why Hard Disk Space Not Correct

Actual Disk Space Calculation and Simple Math Disk Space Calculation!!! Which you prefer?

Most of us will be very curious, why our actually hard disk space does not match with the amount of disk space when we purchase?

For example our 2GB Pen drive, when we check on the disk space, the total space was 1.87GB only (Red Arrow), where another 0.13GB or 130MB missing?

See the image above, the red arrow show 1.87GB, but the green arrow show 2,014,621,696 bytes which already more then 2 billion bytes.

Actual DIsk Space Calculation vs Simple Math Disk Space Calculation

When we talk about actual disk space calculation, bytesKilo bytesMega bytesGiga bytesTera bytes… The disk space is actually count by:

1KB = 1024bytes

1MB = 1024KB (1048576 bytes)

1GB = 1024MB (1073741824 bytes)

1TB = 1024GB

When talk about simple math disk space calculation, the calculation are

1K (kilo) = 1000

1M (Million) =1,000,000

1B (Billion) = 1000,000,000

1T (Trillion) = 1000,000,000,000

For 2GB Pen Drive, if base on disk space calculation, suppose to have 2048MB, , but if base on simple math calculation, 2GB equal to 2Billion is 2,000,000,000 bytes only.

So, how does this actually calculate?

Actual Disk Space Calculation,
Let me give some disk space calculation 1st

Base on the converter, 2GB Disk Space suppose to be = 2048MB = 2,097,152KB = 2,147,483,648Bytes

2,147,483,648 Bytes (Actual 2GB Space) minus 2,000,000,000 (2 Billion Bytes), it is about 147,483,648 bytes. Total different 147MB, which mean if the manufacture use the disk space calculation, then suppose to be 2.15GB disk space for a Pen Drive

Simple Math Disk Space Calculation,
Let see how simple math calculation

Base on the converter, 2GB Disk Space suppose to be 2 billion bytes (2,000,000,000)

2,000,000,000 Bytes equal to 1.86GB only, Total different 140MB, which mean if the manufacture use the simple math calculation, then our pen drive space will be 2GB minus 140MB, and left approximate 1.86GB

Manufacture are base on simple math calculation to provide us disk space, unlike our ram, when we have 1GB ram, it show 1024MB ram in our computer.


Same to 1 Tera Bytes Hard Disk Space, the bigger size the bigger different, and actual disk space only 931GB, which mean 69GB has been missing 😛

Base on the simple math calculation, the 1Tera Bytes is about 1,000,000,000,000 bytes (1 trilion bytes), when using the bytes converter, it will show approximate 931GB.

This is how the hard disk space calculation, so which disk space calculation you prefer?

28 Responses to “Why Hard Disk Space Not Correct”

  1. Wing Loon January 15, 2009 at 12:37 am #

    …simple enough and I saw a 1TB hard disk

  2. El January 15, 2009 at 2:22 am #

    I learn this during my first year computing studies.

    Yet its a good info for non computing related student 🙂

    Thumbs up!

  3. |1f34|-|1r3 January 15, 2009 at 6:51 am #

    many people missunderstood this..same principle applies to bandwidth…you should blog about it…see..i gave you an idea for a blog post..LOL

  4. calvyn January 15, 2009 at 8:48 am #

    |1f34|-|1r3 > Mbps on bandwidth actually not stand for Mega Bytes Per Second, is mega bits per second, also a lot people will confuse about it. Let me find a time, gather some information and will blog about it too 😛 thank for the suggestion

    El > That is great, I never learn this during my academic .until half year ago, i was too free and calculated it, only realize it

  5. foongpc January 15, 2009 at 1:53 pm #

    Thanks for this detailed explanation! Very helpful for people who know very little about such things like me! LOL

  6. www.fabuloustalk.com January 15, 2009 at 7:52 pm #

    I never really personally encounter this before, hope wont. Anyway going to get myself a dell laptop soon, just wondering if dell is a good buy? or acer? Currently I am using a toshiba ones. Been using before IBM, HP, Dell and Toshiba laptops for the past 6 years.But I guess Dell ones is ok with the cheap promotional price they are offering now.

  7. calvyn January 15, 2009 at 8:58 pm #

    for me, I will prefer dell compare to acer. A lot of negative respond out there on acer, but once of my close friend using acer for few year already, so far never heard he complain before, can hv a try if the price is cheaper

  8. yauhui January 15, 2009 at 10:01 pm #

    Haha, actually, i think some of the space has been used for the FAT32 file allocation table data.

    When convert FAT32 to NTFS the space will become even smaller -__-

  9. EVo January 15, 2009 at 11:03 pm #

    Hey!that’s my harddisk man! hehe…eh link back laaaa ..here here.

    Great explanation. now i understand 🙂

  10. ChowSY January 15, 2009 at 11:12 pm #

    The manufacture really take advantage on buyer…

  11. alone January 16, 2009 at 2:12 am #

    oh.. now i know that..

  12. Ryan January 16, 2009 at 2:46 am #

    Seriously, i never knew that. @@

  13. Ryan January 16, 2009 at 2:47 am #

    Forget to say thanks and nice post!

  14. Aizat January 16, 2009 at 10:07 am #

    same goes to external hardisk..

    the bigger space i bought the more space gone.. hehe

  15. TeRaBai January 16, 2009 at 1:15 pm #

    Oh ok. Now i know. Ha ha Ha. been asking myself where does the thing went missing. hahaha. I thought that the memory are being used by certain program wadsoever

  16. Steven January 16, 2009 at 4:31 pm #

    This post sure make things clearer for people who has been wondering why ‘what they bought isnt what they really get’. lol. anyway, I wonder why manufacturers prefer simple math calculation over the actual disk space calculation. Does actual calculation make things more complicated or what?

  17. imDavidLee January 16, 2009 at 11:03 pm #

    ya..u told me b4..so this is the different between RAM and pendrive calculation

  18. calvyn January 16, 2009 at 11:44 pm #

    Aizat > i wonder why they don wan to use another method

    Steven > well, let me check with some HDD distributor, see they hv this kind of knowledge share with me or not…lolz

  19. headsteadi January 17, 2009 at 12:17 am #

    Hi Calvyn

    Thanks for dropping by headsteadi.com

  20. Jayce January 17, 2009 at 8:46 am #

    1TB? I have 512GB only right now. Need to buy another 1TB to over take you. 😛

  21. Angie Tan January 17, 2009 at 9:16 am #

    I was wondering about the history of the megabyte and then recalled my first few lessons at computer class back in school…

    1 byte = 8 bits
    8 bytes = 1 word…

    LOL!! Due to the math calculation, that’s why we get 1024kb = 1MB. 😀

    I got non-IT friends who argue about this… why 1MB != 1000kb …

  22. Bunda January 17, 2009 at 11:13 am #

    wah jadi nambah ilmu ku nih Thx ya 🙂

  23. Jeff January 17, 2009 at 4:08 pm #

    This is good for lotsa ppl.. Answers the question that they all wonder.. “Why i get lesser than I buy?”

    Maybe you should also write about “Why Pendrive space gets lesser and lesser over time?” XD

  24. calvyn January 17, 2009 at 9:56 pm #

    Jayce > The 1TB is not mind, taken from others 😛 I only have largest 80G hard disk only, plan to buy a 350G in next PC fair.

    Angie Tan > Show your friend “byte calculator”, simply search this over google, you can get this calculator already

    Jeff > Hope to see your calculation on pendrive soon 😀

  25. Steven January 19, 2009 at 12:50 am #

    well, thank u in advance =D

  26. ToMCaT January 19, 2009 at 1:16 am #

    Wow… This is a good post.
    I always know that it’s because of the conversion. But this made me clearer about it… =D

  27. gambit November 10, 2010 at 3:44 pm #

    Actually 1024KB = 1MB not 1024kb… b is for bits and B is for bytes.

  28. cris October 23, 2011 at 2:15 am #

    nop, you are wrong
    disk space is not based in “math” calculation (wich probably you mean is base2 and base10 math)

    disk space is always low “for the user” than that is writed in the label just because formating and the FAT/FAT32/NTFS or whatever FAT it uses

    Ill explain to you:

    suppose you have a 16GB disk or memory

    and format it to NTFS using a 4KiloBytes cluster form

    16GB = 16384MB = 16777216KB

    in this case each cluster can store 4KBytes

    16777216KB / 4KB = 4194304 [4KB]clusters

    then you has the name of each cluster can have up to 256 bytes in total, including letter of the unit, path, name of the file, extension

    4194304 [4KB]clusters x 256bytes = 1073741824bytes

    16GB = 16384MB = 16777216KB = 17179869184 bytes
    17179869184 bytes – 1073741824 bytes = 16106127360 bytes for storing our files, wich are divided to 4KBytes cluster

    16106127360 bytes = 15728640KB = 15360MB = 15GB

    Im have a 16GB pendrive
    disk properties says
    16014245888 bytes of capacity

    16106127360 bytes – 16014245888 bytes = 91881472 bytes, near 87MB wich are used for MTF and itself copies, and other internal disk data

    I dont know how calculate how much occupies the MTF, it’s variable

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