Why does Windows report different sizes for directory?

[Muse]

I'm running XP Pro, and when I go to Properties for one of my directories it says:

Size on disk: 6.92 GB (7,440,826,368 bytes)

Well, which is it? 6.92 GB or 7.44 GB? What's the idea?

 

[Nothinman]

They're the same, divide 7,440,826,368 by 1024 3 times to turn it into gigs and you'll get 6.92980957.

 

[Muse]

Originally posted by: Nothinman
They're the same, divide 7,440,826,368 by 1024 3 times to turn it into gigs and you'll get 6.92980957.

OK, this is obviously the answer. But please explain why a gigabyte is not a billion bytes.

 

[Muse]

Hmm, I guess a gigabyte is not a billion bytes. It's 1024 megabytes. 😕 Why do they do that?

Edit: I guess it can be both. From Wikipedia:

A gigabyte (derived from the SI prefix giga-) is a unit of information or computer storage meaning either exactly 1 billion bytes (10003, or 109) or approximately 1.07 billion bytes (10243, or 230)

Link

It further says: The usage of the word "gigabyte" is ambiguous: the value depends on the context. etc...

 

[Gamingphreek]

Its all a numerical hierarchy.

8 bit -> 1 Byte
1 Byte -> 1024 Kilobytes
1024 Kilobytes -> 1 Megabyte
1024 Megabytes -> 1 Gigabyte
1024 Gigabytes -> 1 Terabyte
....

Its just how this measurement system was defined. Why Windows still reports the size in bytes (Or anyone does for that matter) is beyond me...

 

[pmv]

I though we were supposed to say 'kilibytes' 'megibytes' and 'gigibytes' for the 1024 based system now? The normal prefixes now being used for the normal 1000 system?

 

[Motorheader]

Because everything is based on exponential notation - as was highlighted in an earlier reply. Hence you're dealing with the power of 2 - not 5 or 10.

 

[Fox5]

1 2^0
2 2^1
4 2^2
8 2^3
16 2^4
32 2^5
64 2^6
128 2^7
256 2^8
512 2^9
1024 2^10

Tada!
Oh, also sometimes windows will show a higher space used on disk than the file size due to defragmentation or an inefficient file system. (By default, block sizes are 4KB, so no file can be under 4KB in size. Some file systems do support packing of files to get around this.)

 

[Muse]

Originally posted by: pmv
I though we were supposed to say 'kilibytes' 'megibytes' and 'gigibytes' for the 1024 based system now? The normal prefixes now being used for the normal 1000 system?

From the Wikipedia link in a previous post of mine in this thread:

- - - -
1,073,741,824 bytes, equal to 10243, or 230 bytes. This is the definition commonly used for computer memory and file sizes. Microsoft uses this definition to display hard drive sizes,[3] as do most other operating systems and programs by default. By this definition, there are 1,0243, or 1024×1024×1024 bytes in a gigabyte. (This is equivalent to 1,024 megabytes, where one megabyte is 1,048,576 bytes or 220 bytes.) Since 1999, the IEC recommends that this unit should instead be called a gibibyte (abbreviated GiB). Although there is little other usage of the term "gigabyte" apart from referring to memory, file sizes, or storage capacity, the IEC's recommendations are frequently ignored amongst computer professionals, and "gigabyte" is used colloquially to mean 10243 bytes. The standard body JEDEC Solid State Technology Association acknowledges the conflict and the existence of the IEC recommendations but, in recognition of the widespread colloquial usage, continues to recognize the definition of 10243 bytes.
- - - -