Path: utzoo!attcan!uunet!munnari.oz.au!metro!ipso!runxtsa!brucee
From: brucee@runxtsa.runx.oz.au (Bruce Evans)
Newsgroups: comp.os.minix
Subject: Re:  Disk address size in V2.0
Message-ID: <2420@runxtsa.runx.oz.au>
Date: 13 Oct 90 12:24:33 GMT
References: <33146@nigel.ee.udel.edu>
Organization: RUNX Unix Timeshare.  Sydney, Australia.
Lines: 18

In article <33146@nigel.ee.udel.edu> drl@vuse.vanderbilt.edu writes:
>At the risk of being pedantic, I'll vote for 4 byte pointers on disk.
>I think that the 3 byte pointers may represent a micro-optimization

There would be no excuse for 3-byte pointers if the decision was just
between 3 bytes and 4 bytes. However, it is planned for Minix 2.0 to
support the 2-byte pointers in old 1.x file systems as well as 4-byte
pointers in 2.0 file systems, and to byte-swap the pointers as required
to handle disks written by all versions of Minix. The extra code for 3
byte pointers is relatively insignificant and the only complication is
that there is no 3-byte integral type.

3-byte pointers save an indirect block for each file of size 8 blocks
to 10 blocks. In one of my Minix file systems there are 62729 blocks
used and 391 files in this range of sizes. 3-byte inode pointers would
save only 0.6%. This is too small to justify complications.
-- 
Bruce Evans  (evans@syd.dit.csiro.au)