pc/mem.h		1991/0613		Created.
		1991/0614
		1991/0625
		1991/0627
		1991/0629
		1991/0703
		1991/0705
		1991/0706
		1991/0709
		1991/0710
		1991/0711
		1991/0716
		1991/0717
		1991/0718
		1991/0719
		1991/0807
		1991/0808
		1991/1004
		1991/1210
		1991/1214
		1992/0625
		1992/0726
		1992/0804
		1992/0805
		1992/0930		Add ISAMEMSIZE.
		1992/1013		Remove isphys.
		1992/1211		Change SEGMAPSIZE from 64 to 16. (XXX why?)
		1993/0915		Remove USERADDR, UREGADDR. Adjust TSTKTOP. Add KSTACK.
		1993/1013		Add getpgcolor.
		1993/1230		Add globalmem.
		1994/0101		Adjust globalmem. (Bug fix?)
		1994/0311		Add BY2V.
		1994/0322		Add ROUND, rewrite PGROUND.
		1994/0813		Add CRASHSIZE.
		1994/0817		Remove CRASHSIZE.
		1994/1122		Change HZ to 50.
		1995/0105		Add IE (same as IFLAG).
		1995/0418		Add PTEWT.
		1995/0725		Change HZ to 100.
		1995/0726		Change KTZERO to skip over bottom of memory.
		1997/0327		SMP changes: increase MAXMACH. XXX
		1997/0520		Bug fix: SELGDT] and SELLDT bits.
		1997/0810		Format edits. Change TK2MS, MS2TK, move user stack below 2GB.
		1997/0920		Change KSTACK to account for malloc header. (XXX bug fxi?)
		1997/1101		Hw bug fix?: move MACHADDR down to low VM address.
		1998/0916		Increase USTKSIZE, SEGMAPSIZE, add SSEGMAPSIZE.
		1999/0101		Bug fix: parenthesize macro arguments.
		1999/0205		Change MS2TK calculation to allow irregular HZ like 82.
		1999/0207		Change HZ to 82.
		1999/0522		Add BLOCKALIGN.
		1999/1022		Whitespace edit.
		2000/0705		Bug fix?: round in MS2TK.
		2000/1018		Add APM segments.
		2002/0109		Add REBOOTADDR, PDX, PTX. Format edit.
		2002/0228		Change HZ back to 100.
		2002/0326		Remove MS2TK (now a function?).
		2002/0410		Add PTEGLOBAL.
		2002/0412		Format edit. Move GDT into its own page CPU0GDT for VMware.