gerwin wrote:It is totally safe to underclock with the usual ranges of multipliers and FSB (66MHz minimum).
However, only the FSB part can actually be underclocked, since intel locked the Multiplier to a single value on all retail Pentium 3s. Your CPU will remain at 7.5x.
Yep.
Corollary: if you want a P3-featured CPU running at 266MHz, you need a P3-533EB, which runs at 4x 133MHz by default and will run at 4x 66MHz if you drop the FSB. Back in the day these were popular choices for low-consumption homebrew servers. Given the current state of power management it's pretty pointless - any Core i7 (or i3 or whatever) will use far less at idle than an underclocked P3.
And as for "scaling to around 233MHz" - MHz are a very, very bad measure of performance. They only say something within a CPU architecture, not between them. A P3-533EB running a CPU-limited task will do so almost exactly twice as fast as a P3-533EB@266MHz, but that won't make it just as fast/slow as a P2-266 (although that difference will be minimal), let alone a P266MMX or an Alpha 21164-266.
If you just want to slow down your CPU for DOS gaming, switch off L2 cache for a huge hit and L1 for an even bigger one. dropping FSB can of course also help. If you want more options, consider a Via C3 (which may run on your current motherboard) as they have a massive range of things you can disable to lower performance from a baseline level around that of a P3-500 (in the case of the C3-800)