There are the different kernels optimized for ifferent machines, the explanation is after the kernel name Red Hat Linux (2.4.20-8.
smp is for multiple processors
bigmem for big memory?, don't know how big but 2.4 kernel is old so 512MB or 1Gb will be big (or even 256MB)
BOOT for some special arrangement on booting ?
-smp (2.4.20-8smp) pressumable dropping SMP
DOS mean a DOS or Windows bootable partition