First time building a kernel, what processor family do I choose for my T42?
 

So there's always ever been "484" or "686" for preconfigured kernels, to my knowledge. I'm building a kernel for the first time on my own for a slackware 14 install, and in the Kernel Configuration, there's a processor family list with 486 already selected, but my specific processor for the T42 Thinkpad I'm using is a Pentium M which is also an option on the list.

My confusion comes from the 486 option stating
and the Pentium M option stating
My processor is definitely Pentium M, but the 486 processor has worked fine in the past. Further, the choice will also wind up affecting certain packages that are cpu-family specific and I don't know if something that works for 486 will work if I choose Pentium M.

As you can see, I'm quite confused. Can anyone offer any insight here?

In general, either choice should be safe. You might see slightly better performance if you build for the 686 or Pentium M architecture, but it will probably be pretty minor. You should not see any software compatibility problems regardless of which architecture you choose. The only difference is which assembler instructions the compiler will be allowed to generate when building the kernel. A kernel containing only 486 compatible instructions will happily run userspace programs containing instructions introduced with more modern processors. The only thing is that a 32 bit kernel can't run 64 bit user space software, generally, but since the Pentium M is a 32 bit chip and can't run 64 bit software anyways, this should not be a big concern.

There is no harm in using the 486, as it should run on most any i486 and later processor. If you are sure that your processor type, then compiling it for that specific type could give you better performance. You just have to realize that that kernel will not run on other processor types like the 486 built kernel can.

<edit> btmiller's post is more concise. I must have been writing mine when that was posted. </edit>

Ah, brilliant. Ok, well I'll just stick to 486 then. If I'm feeling adventurous later on I may reconfigure and try out the Pentium M option. Thank you for the insight!

If I'm building it for a Pentium M processor, what difference would it make if the Pentium M kernel wouldn't run on other processors?

Basicly, I think of disaster recovery. If your Pentium-M got fried and the replacement that you find that is compatable with your motherboard/bios isn't a Pentium-M, you will have to have a compatable kernel to boot. A way to ensure that is to keep a 486 one installed even though using the Pentium-M kernel. Also, for disaster recovery, a copy of the install medium can be of real help (ie, kernel won't boot).

Ah, ok that makes sense. Ok. Well, like I said I think I'll just stick to the 486 for now and when I'm feeling adventurous I'll maybe check out the Pentium M option.