The Open Group's study into LP64/ILP64 explains their choice fairly well. In particular, it mentions both Digital and SGI's prior experience with porting code t

The Open Group's study into LP64/ILP64 explains their choice fairly well. In particular, it mentions both Digital and SGI's prior experience with porting code to LP64. There's nothing about SCO's preferences in it. http://archive.opengroup.org/public/tech/aspen/lp64_wp.htm http://archive.opengroup.org/public/tech/aspen/lp64_wp.htm "By far, the largest body of existing code already modified for 64-bit environments runs on LP64 based platforms."