Linux.com: Linux, Windows NT, and the Pentium 4Dec 20, 2000, 20:47 (1 Talkback[s])
(Other stories by Brian Richardson)
"As you may well know, the Intel Pentium 4 is not getting along well with Linux these days. Unless you run a patch on your distribution, or upgrade to the 2.2.18 kernel, Linux recognizes the Pentium 4 as an "unknown processor." Most Linux users see this as a reason to attack Intel for not working closely with Linux developers. The real reason for this processor problem is an odd tale which has roots in Microsoft Windows NT...."
"Intel identifies its various processor using a combination of the family and model codes. Pentium processors are identified by a family code of 5. A family code of 6 covers the PentiumPro and all of its variants. Since the PentiumPro, Pentium II, Pentium III and Celeron are all based on the same processor architecture, they are all part of the P6 family( hence, family code 6). The model code is used to tell the various P6 processors apart, along with the cache size and brand ID, depending on the CPU (it's messy; don't ask)."
"Intel decided to make a new family code for the Pentium 4. That's where the fun begins."