# 2.5" HD question

#### minimax

##### macrumors 6502
Original poster
Might be a stupid question...but my present 3.5" desktop PC HD features a so called 40 GB harddrive which in reality is 37.25 GB (1:1.024:1.024:1.024)
Is this common for all harddrives?

I'm thinking about buying a mini and doubting over a 40 or 80 GB harddrive. The difference is small, but still, if the Seagate REALLY is 40 GB it might just be enough for me.

#### robbieduncan

##### Moderator emeritus
This is standard to all harddrive manufacturers. They use round numbers, whereas computers use powers of 2 that result in this difference. The 40Gb drive in a Mac is the same as a 40Gb drive in a PC.

Edit to add see note 1 at the bottom of the Mini specs

It could be argued that 1 Gb should equal 1073741824 not 1000000000 which is where most of the space differential is (the other arguement is that giga is a SI prefix so the drive manufacturers are correct).

#### feakbeak

##### macrumors 6502a

Hard drive manufacturer's advertise the size of their hard drives with 1 GB = 1 billion bytes.

Computer show hard drive size with the true value of a GB. 1 GB = 1073741824 (2^30) bytes.

So, 40,000,000,000 bytes divided by 1,073,741,824 bytes = 37.25 GB that you see reported back by the OS.

I have a Mac mini and I got the 80 GB drive and I'm glad that I did. I actually have a spare 40 GB external firewire drive that I don't even use. I could have ordered my mini with 40 GB and hooked that up for 80 GB, but the truth is it would look clunky and my external hard drive is noisier than the mini itself. I have my mini out in my living area and I wanted it to look slick.

#### minimax

##### macrumors 6502
Original poster
ah yes indeed it is mentioned on the mac mini site, didnt pay enough attention.

thanks for the info people!

btw the argument of giga as a SI prefix doesnt hold ground since memory uses the 1024 ratio instead of the 1000 for prefixes. They should both use either the one or the other to avoid confusion. oh well.

#### Yvan256

##### macrumors 603
Actually, giga is a metric prefix that means 1 billion bytes.

When the computer industry started, they "borrowed" metric prefixes since "1024 is close enough to 1000".