Difference Between bits and bytes?

Posted on 2005-03-29
Medium Priority
Last Modified: 2011-08-18
I have an harddrive with a capacity of
81,956,655,104 bytes 76.3 GB

how is that possible when a byte is 8 bits?
what is GB? and is it the same as Gb?

how can i have 82,000,000,000 bytes but only have 76.3 GB?  Something isn't adding up here.  Can someone put my confusion to rest.

and how come 1 byte is 8 bits yet 1 kilobyte = 1024.

I know theres something i'm just not getting, cause this can't be that confusing.
Question by:Xygus
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LVL 96

Accepted Solution

Lee W, MVP earned 500 total points
ID: 13655217
Everything is a factor of 2.

1 bit = 1/8 byte.  A bit can be a 1 or a 0.  This is not enough info to represent a set of characters, A, B, C, etc.  8 bits allows for 256 different combinations, more than enough to acomodate an alphabit and supporting symbols.  These are referenced with a lowercase "b" - Mb, Kb, b, etc.
1 byte = 8 bits (with 256 combinations).   These are referenced with an uppercase B, GB, MB, KB, B, etc.
1 KB is ROUGHLY equal to 1,000 BYTES (not 1000 Bits), actual 1024 BYTES or 8192 BITS.  which happens to be 2 to the power of 10 bytes.
1 MB is 1,048,576 BYTES.
1 GB is 1,073,741,824 BYTES.

When manufacturers advertise an 80 GB hard drive, they are advertising as if 1 GB = 1,000,000,000 bytes.  But since it doesn't; since it's more, the actual amount the computer sees is less (80,000,000,000 / 1,073,741,824 = 74.5 GB to the computer).

Make sense?
1 MB is ROUGHYL equal to 1,000,000 BYTES (

Expert Comment

ID: 13655357
In addition some space is lost on the drive to the user due to the file allocation methods for the file systems thus the total amount of hard drive space available to the user is usually less than the advertised amount
LVL 10

Expert Comment

ID: 13655961
8 bits are equal to 1 byte.

1,024 bytes are equal to 1 kilobyte (Kb).

1,024 kilobytes (Kb) are equal to 1 megabyte (MB or Meg)

1,024 megabytes are equal to 1 gigabyte (Gb or Gig)

1,024 gigabytes are equal to 1 terabyte

Large Disk HOWTO Units and Sizes


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Bytes, Kilobytes, Megabytes, Gigabytes and Beyond


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Byte (B), kilobyte (kB), megabyte (MB), gigabyte (GB), terabyte (TB) and petabyte (PB)


LVL 13

Expert Comment

ID: 13656217

Leew has it right; the confusion arises from the fact that a "K" is technically 1,024, but it often thought of as 1,000.  Since "mega" is "K-squared", and giga is "mega times K", the matter of whether you are being "precise" and call a "K" 1024, or being "approximate" and call a "K" 1,000 starts to become significant.

The two ways of giving sizeshave been given names, it's called a "binary" "K" or "mega" or "giga" if you use the power of 2 number (1,024) and a "decimal" "K" or "mega" or "giga" if you use the power of 10 number (1,000).  And there is another issue:  Marketing, and Money.  If you use the decmal numbers, any given disk drive is "bigger", so the disk drive makers all use the decimal numbers.  And to make matters worse, the IEEE has actually sanctioned and officially recognizes the decimal definitions for disk drives, and, I think, for flash memory.  But not for DRAM (main system memory).  And Microsoft uses binary units when they show the size of things (including disk drives) within Windows.

[Bits -- Binary digITs -- don't really enter into this in any significant way, although a byte is indeed 8 bits, as the term is commonly used today.]


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