See Mike's link for an explanation...
  -----Original Message-----
 From: Jules Richardson [mailto:julesrichardsonuk at yahoo.co.uk]
 Sent: Tuesday, July 05, 2005 4:58 PM
 To: cctalk at 
classiccmp.org
 Subject: Re: IBM AT Drive Types
 Home come entry 15 was reserved? (and why pick 15?)
 cheers
 J.