36.4GB drive formats out to 32.8GB? what am I missing please

[D. Goss]

I am adding some drives to an IBM xSeries 345.  I recently picked up  
(via eBay) an IBM packaged Seagate drive, all with the proper IBM  
part numbers as:

U320 15k
36.4GB formatted capacity
(IBM part 06P5776 / 06P5778, with Seagate drive ST336753LC)

Looking up both the IBM part numbers and the Seagate part numbers via  
Google, I consistantly get that the drive's formatted capacity is  
36.4GB.

When partitioned either in "safe" or "dd" mode (via sysinstall) and  
set to use the entire disk as one slice, once the drive is mounted I  
show:

# df -m
/dev/da1s1      33617    0 30928     0%    /misc

# df -h
/dev/da1s1      33G    4.0K     30G     0%    /misc

I'm seeing approx. 30,600MB (32.8GB?) free -

Is this correct?

Thanks!