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Date: Sat 11 Mar 89 12:09:58 PST
Subject: Info-Atari16 Digest V89 #78
From: Info-Atari16 Digest <Info-Atari16@edu.stanford.score>
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Info-Atari16 Digest   Saturday, March 11, 1989   Volume 89 : Issue 78

This weeks Editor: Bill Westfield

Today's Topics:

                   Hard Disk Partitioning Tutorial
                 atariST TOS gcc V1.34 avail for FTP
                Atari 1040 ST, modem, printer for sale
                         Zoo compression prg
                                 SEDT
                       Bulliten Board Systems.
                      Leaving both monitors on.
                   RE: Info-Atari16 Digest V89 #43
                               Re: SEDT
                      Adaptec controller boards
                             Atari 520ST

----------------------------------------------------------------------

Date: 6 Mar 89 14:30:18 GMT
From: att!lzaz!hcj@ucbvax.Berkeley.EDU  (HC Johnson)
Subject: Hard Disk Partitioning Tutorial
To: info-atari16@score.stanford.edu

This is meant to be a tutorial on partitioning a hard disk connected
to an Atari ST computer.  It will address TOS, Minix, PC-Ditto, and 
Spectre 128 usage.

There is considerable mysticism about the partitioning hard disks for
the Atari.  It isn't as complicated as it may appear.  

OVERVIEW

A hard disk is just a collection of sectors, numbered 0 to MAX, where
MAX is the total good sectors on a given hard disk.  Within most of the
disk interfaces is an Adaptec 4000 controller.  When told which sectors
are bad this device automatically squeezes them out, leaving MAX-N good
sectors.

Rule one:  Always subtract a reasonably small (128) number from the total
size of the disk to allow for this shrinkage.

PARTITIONS

Partitioning is just a way of thinking of the whole disk in parts.  It
occures in UNIX and MS-DOS because the original files systems could not
exceed numbers which were small compared to the total disk.  The most
current limit is TOS, which cannot handle a file system larger than
16 megabytes (32767 sectors of 512 bytes each). 

Sector 0 of the hard disk holds three kinds of information.  Within a
total of 512 bytes there exists:  First, an area reserved for a boot program.
Second,  sixteen bytes to describe the physical parameters of the disk; and 
ten bytes to support bad sectoring.  Third, an array of four partitions.
Each entry in this array describe the partitions storage area on the disk.

This is the 'C' description of a partion:

/*
 * Partition information (part of sector 0)
 */
struct pi {
  char	pi_flag;		/* active byte */
  char	pi_id[3];		/* partition id (GEM or MIX(?)) */
  long	pi_start;		/* first sector */
  long	pi_size;		/* total number of sectors */
};

If a partition is allocated, the flag is set to '1', and the  size is set
to the actual size of the partition is sectors.  Usually both the flag and
size will be 0 when a partition is unused.  Start is the actual physical
sector of the hard disk where this partition begins.  Within the partition
we talk of logical sector numbers from 0 to size -1. Additionally the 
partition may have a name (ID) to descibe who might expect to use it.

It is not uncommon to find several different names in the partitions, to
indicate that each different name is organized logically different from
the other.
Some examples of this:
A. TOS and PC-Ditto can process partions containing MS-DOS file systems.
   They use the ID 'GEM' to indicate this.  When they boot, only the 'GEM'
   partitions are given ICONs on the desktop.  Intervening partitions of
   other types are ignored.  Thus the First GEM partition is called C:, 
   the Second GEM partition is called D:, etc.

**** Rest omitted - too long!