Why Hard Disk and Memory Cards Have Smaller Size than Advertised Capacity?

You might noticed that your computer shows the size of your Hard Drive little less as compared to the size promised by the manufactured company or as labelled on the box.For instance,  You bought a new PC and in its configuration it is written that it has 500 GB hard disk drive.But when you boot it up ,the operating system showing the total size of Hard disk  drive is 465 GB. Where the 35 GB of storage gone? Do the computer manufactured company cheated you ? Well, this difference  is due to the different number system used by humans and digital circuits.

Humans think of numbers in base 10,that is ,we calculate as follows:
    1ooo bytes = 1 kilo
    1000 kilo   = 1 mega
    1000 mega = 1 giga and so on.

On the other hand, for computers,  
    1 kilobyte    =  1024 byte
    1 megabyte = 1024 kilobyte
    1 gigabyte   =  1024 megabyte.
All the hard drive and computer manufactures consider 1 MB equal to 1,000,000 bytes and 1 GB equal to 1000 MB whereas the correctly, 1 MB is 1,048,576 bytes and 1GB is 1024MB.
For each Gigabyte ,you are actually getting 70 megabyte less storage space because of difference in number systems used by manufactures and computers. 

Same is the reason for USB  drives and memory cards.However, for these devices the difference is less because of small capacity.As the storage capacity increases, the difference keep on increasing .If you buy an external hard drive of one terabyte ,you will get about 70 GB of less space than a terabyte.

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