Actual size of USB drive not displayed

By robvilla
Nov 7, 2007
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  1. I have a new 80Gb USb drive, but the computer only says it's about 76.53 Gb, where's the remaining 3+ Gb?
  2. Ph30nIX

    Ph30nIX Newcomer, in training Posts: 359

    It is the way the drives are labeled. Hard drive manufacturers use 1000 bytes for a megabyte and windows sees it as 1024 per megabyte. Its just how it is these days. Any 80gb hard drive you buy will be 76gb when you put it into an operating system.
  3. jackazz76

    jackazz76 Newcomer, in training

    I'm not sure if this is the case, wait for a better response from the pro's. At least a hard drive never reports it's actual size because some of the disk is used for boot record and file system architecture. When it is formatted some space is used up for these things. Some also come bundled with tools.


    *see I shoulda waited and avoided being upstaged (putting head in sand)
  4. Ph30nIX

    Ph30nIX Newcomer, in training Posts: 359

    Im sure thats how it works, its the way they use bits and bytes etc. (1000 vs 1024) Im just not sure what level it starts on etc. I have seen this problem asked so many times in the forums its just ridiculous.
  5. Nodsu

    Nodsu Newcomer, in training Posts: 9,431

    That's exactly how it is. Storage manufacturers define a gigabyte differently to make their devices look bigger.
  6. technicalfury42

    technicalfury42 Banned Posts: 109

    Let's see if I can get rid of some of the nonsense, conjecture, and random statements about this from people that don't know:

    The problem is drive manufacturers use decimal instead of binary.

    (80 * (1 000^3)) / (1 024^3) = 74.505806

    An 80GB drive calculated in this way should be slightly less than 74.5GB after format.

    Now, as for why your drive is 76.5 and not 74.5GB, as I've indicated, there is a very simple reason.

    Your USB drive is *waves magic wand* a Retail Maxtor hard drive (if you were to crack open your external drive's case, this is what you'd discover). Maxtor has made many 82GB drives (retail) marketed at 80GB, while their OEM drives are actually 80GB. This accounts for the discrepancy in the math. I suspect we would also find that your size is closer to 76.3, not 76.5, and that you rounded or mistyped?

    (82 * (1 000^3)) / (1 024^3) = 76.3684511

    Here are a few more common reductions:

    (74 * (1 000^3)) / (1 024^3) = 68.9178705 (74GB = 68GB)
    (160 * (1 000^3)) / (1 024^3) = 149.011612 (160GB = 149GB)
    (250 * (1 000^3)) / (1 024^3) = 232.830644 (250GB = 232GB)
    (320 * (1 000^3)) / (1 024^3) = 298.023224 (320GB = 298GB)

    A quick analysis will show that current drive sizes are actually reported about 93% of the size that they are marketed. In other words, you can make a really rough estimate by reducing the size of the drive 7GB for every 100GB. i.e. a 500GB drive would be a rough estimate of 465GB.

    (500 * (1 000^3)) / (1 024^3) = 465.661287
  7. zipperman

    zipperman Newcomer, in training Posts: 1,423   +7

    My 160 is totalled at 149.1.
    Doesn't worry me as i know it's rounded out by 1000,not 1024.
    You or I didn't get ripped off.
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