Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!apple!altos!altos86!robk
From: robk@altos86.Altos.COM (Rob Kleinschmidt)
Newsgroups: comp.arch
Subject: Re: 64-bit addresses
Message-ID: <285@altos86.Altos.COM>
Date: 23 Feb 90 20:37:02 GMT
References: <9708@spool.cs.wisc.edu> <20270@cfctech.cfc.com> <36080@mips.mips.COM> <168@csinc.UUCP> <986@m1.cs.man.ac.uk> <43437@ames.arc.nasa.gov>
Reply-To: robk@altos86.UUCP (Rob Kleinschmidt)
Organization: Altos Computer Systems, San Jose, CA
Lines: 23


A couple of questions re additional memory needed to run in a 64 bit
address space:

1)	Would anyone care to speculate on page sizes and layouts
	for mmu descriptors ? Seems like the dimensions of these
	items get very big quickly. Does the problem get better if
	we avoid building knowledge of mmu tables/levels into hardware ?

2)	How much additional memory would be needed to run a garden
	variety program that is happy in a 32 bit environment ?
	My bet would be that data space doubles.

3)	Other space wasted by allocation due to larger page sizes ?

4)	Possible increases in bus traffic due to normal stack accesses
	etc. ? Possible increase in context switch overhead ?

5)	Applicable data from early 16 to 32 bit ports ?



Rob Kleinschmidt