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Thread: Why SSD acual capacity is different with Disk capacity?

  1. #1
    Join Date
    May 2011

    Default Why SSD acual capacity is different with Disk capacity?

    Many users are very confused that why real capacity is different with capacity they ordered. I collected some information and share with yours.

    The disk capacity doesn't match with the actual capacity caused by the different algorithms of OS and Hard Disk.
    Hard Disk manufacture caculated by 1000Byte=1KB,1000KB=1MB,1000MB=1GB:
    But operation system caculated by 1024Byte=1KB, 1024KB=1MB, 1024MB=1GB.
    So, the relationship between disk capacity and OS acual capcity should be :1000*1000*1000/1024/1024/1024=0.93132257461547815625

    Let's take 256GB Nand flash as example, So,256GB*0.931322=238.4GB.

  2. #2
    profJim's Avatar
    profJim is offline Chief Munchkin + moderator
    Join Date
    Dec 2008
    Tacoma, WA. [USA]

    Default Re: Why SSD acual capacity is different with Disk capacity?

    To put it another way:
    1024 x 1024 x 1024 =1,073,441,824
    This means that the disk manufacturer's published disk size is about 7.34 % higher than the o/s reported disk size.
    This applies to HDDs and SSDs.
    In the example in post #1, the reported disk size is 93.8% of the OEM reported disk size.
    With many/most solid state drives, some disk capacity is held in reserve for “over provisioning”. A web search using over provisioning ssd will explain this feature.

    Check out Solid-state drive - Wikipedia for more information.
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