[ILUG] Shameless plug

[Niall O Broin]

On 30 Apr 2008, at 20:48, Michael Watterson wrote:

> basically it's because memory chips use pwr of 2 due to binary  
> addressing  ( 1024 = 10 address lines)
>
> Disk drives however count with decimal pwrs of ten

Disk drives don't count with anything, but disk drive sector  
addressing is just as much power of two related as is memory. There's  
one and only one very simple reason why manufacturers of disk drives  
are quite happy to be technically correct in their usage of gigabyte  
to mean 1,000,000,000 bytes and that's marketing - if engineering  
produces a disk drive which can store 100,000,000,000 bytes marketing  
wants to sell that as a 100 GB (gigabyte) drive rather than a 93 GB  
(gibibyte) drive.

This difference in capacity between what manufacturers (which speak  
in gigabytes), and what operating systems (which speak in gibibytes)  
say has existed for a long time (witness the 1.44 MB diskette) but  
users knew that operating system formatting used up some space on the  
disk, so when they installed a 100 MB disk drive and ended up with  
the operating system saying there  was ~95 MB available that wasn't  
such a big deal - it was only ~4 MB. But when you buy a 100GB disk  
drive and end up with the operating system saying there is ~93 GB  
available that's 7GB you appear to be short  and a significant number  
of people know that this is a fairly big chunk of space (of course an  
even more significant number of people wouldn't know a byte if it bit  
them, but they're not germane to this discussion).

This is evidently such a cause of confusion / annoyance to the punter  
that a computer store I visit occasionally has a sign up on the wall  
explaining this, presumably to head angry customers off at the pass.


Niall