Path: utzoo!mnetor!uunet!husc6!mailrus!nrl-cmf!ames!ucsd!sdcsvax!earle@mahendo.Jpl.Nasa.Gov
From: earle@mahendo.Jpl.Nasa.Gov (Greg Earle)
Newsgroups: comp.os.research
Subject: O/S's using bit maps for free disk block lists?
Message-ID: <4811@sdcsvax.UCSD.EDU>
Date: 29 Mar 88 08:13:08 GMT
Sender: nobody@sdcsvax.UCSD.EDU
Organization: Gainfully Unemployed Ltd., Lakeview Terrace  CA
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Approved: comp-os-research@ucsd.edu


In Maurice Bach's `The Design Of The UNIX Operating System' book, the last
Exercise in Chapter 4 (Internal Representation Of Files) reads:

	15. Discuss a system implementation that keeps track of free disk
	    blocks with a bit map instead of a linked list of blocks.  What
	    are the advantages and disadvantages of this scheme?

I once worked on a project (a proprietary database computer, not unlike that
made by Britton-Lee) where the O/S team member designing the file system used
the bitmap scheme for the free disk block list.  Seeing this exercise got me
curious as to whether anyone has tried implementing this as a research project
using a UNIX system as a base, or conversely, do any extant O/S research
projects use this method?  If so, can anyone answer the question above (namely
how does it compare to using a linked list, kept in the Super Block)?

[ I know VMS uses bit maps.  --DL ]


-- 
	Greg Earle		earle@mahendo.JPL.NASA.GOV
	Indep. Sun consultant	earle%mahendo@jpl-elroy.ARPA	[aka:]
	(Gainfully Unemployed)	earle%mahendo@elroy.JPL.NASA.GOV
	Lake View Terrace, CA	...!{cit-vax,ames}!elroy!jplgodo!mahendo!earle