Stuff that pertains regardless of 386 mode-oids. Basic memory locations in
legmeg, basic GDT, PIC programming, PE and CS switchers, etc.

Ha3sm sources are grouped by the two most important bits in the machine,
PE, Protection Enabled in CR0, and Dbit, the default bit in the current
code segment under CS. two bits is four cases. Stuff in here is more
fundamental than those two bits, or crosses cases.

