Both are double sided, but the Kingston modules have slimmer memory chips. The Kingston fits perfectly in the ram socket following the side of the Blizzard PPC, where as the HP will get in contact with the heatsink holder.
Depends on which accelerator you wish to use the modules in I suppose. If it's a Blizzard 1240 or 1260, it most likely will need to have the 45 degree angled memory socket. The Kingston modules might be able to fit in an accelerator without the 45 degree angled socket, but the CPU needs to be without heatsink then.
The HP modules have these dimmensions in mms (width x height x thickness) = 108 x 36 x 8. The dimensions of the Kingston modules are 108 x 38 x 3 at the thinnest spot, but unfortunately still 8 mms thick at the side were the 72 pins are found :-(
