Xref: utzoo comp.sys.amiga.tech:7565 comp.sys.amiga:41584
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uakari.primate.wisc.edu!ginosko!uunet!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.amiga.tech,comp.sys.amiga
Subject: Re: More dos questions
Message-ID: <8181@cbmvax.UUCP>
Date: 13 Oct 89 15:55:14 GMT
References: <5599@ucdavis.ucdavis.edu>
Organization: Commodore Technology, West Chester, PA
Lines: 21

in article <5599@ucdavis.ucdavis.edu>, rogers@iris.ucdavis.edu (Brewski Rogers) says:
> Keywords: dos,sod,dso,osd
> Xref: cbmvax comp.sys.amiga.tech:8243 comp.sys.amiga:44101

> 1.	How exactly is Seek() implemented? If I Seek 200K forward, will dos
> read through all the data until it gets there, or does it have some way of 
> figuring out where to move the head to? If it does have a way of knowing
> where to move the head to, is the information easily found, or does it
> have to move the head to find it?

Each file header contains pointers to the first 72 data blocks.  If a file
is longer than that, the file header will have a pointer to an extension 
block, which points to the next 72 data blocks, and also has an extension
block.  So to seek ahead 200K, the filesystem will have to move through 
5 extension blocks to find the pointer that references the block at 200K.

> 2727 Eel                   Bruce (6502 RULES!) Rogers        |\  Duck  ( 0 0)
-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough