Drives have different sizes on dif OS's. Why?

Hello folks,
I hope this is in the right forum heading.
I will start with the setup.
I have 2 drives hooked up to an Airport Extreme.
I have 1 MacBook 10.6.2, 1 iMac 10.3.9 and 1 PC XP accessing the drives through the network.
Drive 1 is a WD elements. 640gb
On the PC it shows as total size 596gb
On the MacBook it shows as total size 640gb
On the iMac it shows as total size 596gb

Drive 2 is in an iomega case. 20gb
On the PC it shows as total size 18.9gb
On the MacBook it shows as total size 20.35gb
On the iMac it shows as total size 18.9gb

Have apple changed the formula for the way it reads the size of drives? And is this why when everyone who installed 10.6 saw their drive space increased?

Any thoughts?

nevyn68 said:

Have apple changed the formula for the way it reads the size of drives?

Click to expand...

Yes they have. Windows and OS X pre-10.6 measure hard drive space using base 2 notation (1MB = 1,024KB) while OS X 10.6 and HD manufacturers use base 10 notation (1MB = 1,000KB). This is why your HD shows up as "the correct size" in Snow Leopard. My 320GB HD is reported to be 319.73GB while in Leopard, it was ~298 (I think).

This was indeed changed for Snow Leopard. Drive manufacturers report their drive capacities in base 10 (the numbers we are all familiar with). Until Snow Leopard the OS reported drive capacities in Binary (base 2). The resulting "loss" of size is due to differences in these number systems. One GB binary is not exactly the same as one GB decimal. Windows is still using base 2 unless that changed with Win 7. How Mac OS X reports drive capacity

Thanks folks