# HD Question

Discussion in 'Mac Pro' started by G.Kirby, Apr 25, 2007.

1. ### G.Kirby macrumors regular

Joined:
Feb 15, 2005
Location:
Swansea, South Wales
#1
We have just had a new MacPro with 500Gb HD installed. But, usable space is only about 450Gb. I know that formatting requires space but 50Gb?

We have the same problem with a 200Gb MacBook Pro.

I feel like I have just bought a new car and found it has no steering wheel.

2. ### zero2dash macrumors 6502a

Joined:
Jul 6, 2006
Location:
Fenton, MO
#2
I have a 320g Seagate.
If the drive is empty - it registers as 298g.

It's the way hard drives are.
Chalk it up to that + the OS/app installation space taken up.

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#3
http://en.wikipedia.org/wiki/GiB

long standing issue with HDD vendors, they quote capacity in gigabytes, but the OS reports gibibytes which give you automatically a 8% reduction in space.

a 500 GB drive only has 465.6 GiB, which is usually what the OS reports.

500*1000*1000*1000 = 465.6*1024*1024*1024.

B

4. ### G.Kirby thread starter macrumors regular

Joined:
Feb 15, 2005
Location:
Swansea, South Wales
#4
Just been doing some maths. Looks like there is a consistent ratio to the size of HD and the amount of space after formatting. The magic number looks to be a ratio of 1.074.

So if you want to know how big a HD will be when formatted do this bit of maths.

Proposed HD size (eg 500Gb)
Divided by 1.074
Gives you your usable HD size (465.5Gb)

5. ### G.Kirby thread starter macrumors regular

Joined:
Feb 15, 2005
Location:
Swansea, South Wales
#5
Thanks, I think That's some proper Maths there lol

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#6
1.0737=1.024*1.024*1.024 (see the article I linked above).

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