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Path: utzoo!aesat!bmw
From: bmw@aesat.UUCP (Bruce Walker)
Newsgroups: net.micro,net.micro.trs-80,net.micro.pc
Subject: Re: formatting ST506 winchesters (naive question)
Message-ID: <587@aesat.UUCP>
Date: Tue, 25-Mar-86 09:11:41 EST
Article-I.D.: aesat.587
Posted: Tue Mar 25 09:11:41 1986
Date-Received: Tue, 25-Mar-86 09:12:29 EST
References: <321@hadron.UUCP>
Reply-To: bmw@aesat.UUCP (Bruce Walker)
Organization: AES Data Inc., Mississauga Ont., Canada
Lines: 59
Summary: 

In article <321@hadron.UUCP> tsp@hadron.UUCP (T. Scott Pyne) writes:
>[...] when formatting an ST506
>Winchester,  in this case a Tandon TM502 in a Tandy 2000,  does (can)
>the formatting program know,  or have to know, beforehand how big the
>disk in question is?   I am interested  in swapping the  10Mb disk in
>my 2000 for a larger  (35Mb?  70Mb?) disk [...]
>so what
>happens when I power the system up with, e.g., a 35Mb disk?  Does the
>formatter find out that the disk is 35Mb and work OK? 

[The follwing remarks pertain to PC (& PClone) compatible controllers]

The hardware (controller) itself knows how big the disk it controls
is.  The disk controller's firmware ROM has a four entry table which
contains values for such esoterica as: number of cylinders, # of heads,
where the write precomp should start (if any), etc.  A set of DIP
switches or (more usually) plug jumpers on the controller board is
consulted during the POST (Power-On Self Test) to determine what sizes
of drives are attached.

Now, it starts getting tricky.  The sequence for formatting (on a stock PC)
is as follows: "hard" format using the Advanced Diagnostics disk; set up
partitions and a boot block with FDISK; finally "soft" format with FORMAT.

I differentiate between "hard" and "soft" formatting because the DOS
FORMAT program is badly named (at least for its role with hard disks).
It does *not* format the hard disk, it reads all the sectors (which
must have been *pre*formatted), zeroes the FAT, marks bad clusters in
the FAT, and zeroes the directory area (in UNIX parlance, it is like
"mkfs(M)" ).

On other DOS'es, the names are changed to protect the guilty (and confuse
the innocent), but the sequence is the same.

The hard format program is required before any disk can be used.  It can
format any size disk (within the capabilities of the controller itself).
Depending on the version of DOS, FDISK can partition different amounts of
disk - PCDOS 2.1 can only handle about 32Mbytes while 3.1 can handle up
to (approx) 130 Mbytes.  With the "standard" DOS disk drivers, however,
a DOS partition may only be up to 32 Mbytes (with any version of DOS).
Some third-party large disk vendors supply new disk drivers which allow
very large partitions and / or multiple "logical" drives to get DOS to
handle up to the 130 Meg capabilities of the drives.

So, to alter your system to take a bigger drive, you may have to get a
new disk controller ROM with the appropriate entry for the new drive size,
and if it is bigger than 32 Meg, get a new driver to allow DOS to use it.
Most controllers available today know how to talk to "standard" 20 Meg
drives (typical half-height Seagates and Shugarts (225's & 725's), etc),
so that combination is easily installed.  However getting a 45 or 70 Meg
disk to live in your system is much more of a trick (although, if your
goal is to run a UNIX package, they may make your life easier by supplying
configurable drivers).


Bruce Walker     {allegra,ihnp4,linus,decvax}!utzoo!aesat!bmw

"I'd feel a lot worse if I wasn't so heavily sedated." -- Spinal Tap