Yes, the diagnostics disks are used for CMOS setup on the AT. 'DEBUG' alert .. ) hard core for me. The Advanced Diagnostics that I mentioned is for the PC and XT, and came with the hardware maintenance and service manual. It has the low level format routine for the 10MB XT hard disk, which is useful if your controller doesn't have an onboard routine to do it. (I'm not sure which ones do and don't.) The regular Diagnostics disk are for the PC and XT, and are also a good test of clone compatibility. Do not run them on a PCjr. :-) Mike