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Date:         Wed, 23 Dec 1992 11:07:00 CST
From:         Lance Tagliapietra <96720919@UCS.UWPLATT.EDU>
Subject:      Re: Amiga file system and operating system

>Date: Wed, 23 Dec 1992 09:18:03 MST
>From: dleland@NMSU.EDU
>Subject: Amiga file system and operating system
>
>I've been trying to find some basic information about how the Amiga's
>file system and operating system differ from other PC operating systems.
>I understand there have been some real improvements to the FFS and something
>called directory caching (please, I really don't know anything about this
> stuff).
>added to 2.1. What does it do? How does the Amiga store and organize files?
>What is good/bad/indifferent about it?
>Also, what exactly is intuition, the ROM kernel and so on? If this is an FAQ,
>where can I get this information (yes I know, another "where can I find..."
>posting).
[...]
>
>Darrell Leland
>dleland@nmsu.edu

Most of your questions can be answered in The AmigaDos Manual, 3rd Edition,
by Bantam Computer Book.  You should be able to find it in a good bookstore
(I bought mine at a Waldenbooks).  The filesystem is detailed in this book
as are all the AmigaDos cli commands and AmigaDos function calls.

The AmigaDos filesystem can be somewhat slower reading a directory from
a disk, because directory information is scattered all over an AmigaDos
volume.  This is offset by the fact that once AmigaDos reads in a directory
entry, it saves it in a buffer.  AmigaDos directory entries are connected
by a double-linked list.  If a portion of a disk becomes corrupt and causes
a directory entry to become unreadable, only that particular file might
be unrecoverable.  MS-Dos holds the directory on the outer tracks of the
disk.  If those tracks become worn out, you could loose the entire directory
for the disk.  AmigaDos starts placing directory information near the middle
tracks of a disk.  This way searches for extended directory entries tend to
be shorter than on MS-Dos disks.

Intuition is that portion of AmigaDos which handles Amiga GUI input events.
For example, the routing of keyboard input to the currently selected window.

The ROM Kernal -- AmigaDos is on ROM, as opposed to a MS-Dos system, where
MS-Dos has to be loaded from disk.  The ROM holds the "core" or Kernal
routine for AmigaDos.  The Rom Kernal Manuals published by Addison Weseley
describe how to use these "low level" routines.  An advantage to having the
operating system in ROM is that a program that has crashed cannot write
over the operating system, which can be very common in an MS-Dos system.

One of the strengths of AmigaDos is that it is re-entrant.  MS-Dos is not.
That means when writing an interrupt routine under MS-Dos, the routine
cannot use any other MS-Dos functions, because you are already in MS-Dos
as part of the interrupt. (Some would say that MS-Dos is not an operating
system anyway, but just a non-reentrant interrupt handler, as MS-Dos
functions are called through software interrupts).

Anyone else care to add to this description for Darrell?

-Lance
 ---------------- Amiga - The Wild Side of Power Computing -----------------
 Lance Tagliapietra                       Internet: 96720919@ucs.uwplatt.edu
 P.O. Box 26                                BitNet: 96720919@uwplatt
 Platteville, WI 53818
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU