To:	opendos AT delorie DOT com
Date:	Fri, 16 Feb 2001 03:26:24 -0800
Subject:	Re: Max. drive letter, etc. (was Hard Disk 20gb and dos)
Message-ID:	<20010216.032625.-270235.0.domanspc@juno.com>
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From:	Robert W Moss <domanspc AT juno DOT com>
Reply-To:	opendos AT delorie DOT com

From 'Upgrading and Repairing PC's', by Scott Mueller, 
sixth edition, 1997, QUE Books.  ISBN: 0-7897-0825-6..... 

PAGE 762: 

SCSI

Most systems support up to four SCSI host adapters, 
each with with up to 7 hard disk drives for a total of 28 
physically installed drives. 

(Since this book was published I recall reading some 
place about a new super wide SCSI setup where you 
can install 16 devices per adapter.)  (?) 

ROM BIOS CAPACITY LIMITATIONS 

In addition to the capacity limit of 504M, the standard 
ROM BIOS is limited to supporting only two hard disk 
drives.  The enhanced BIOS is limited to 128 drives 
maximum.  Most SCSI and IDE adapters get around the 
standard BIOS two-drive limits by incorporating an 
enhanced BIOS on board that  takes over the disk 
interface.  Some of the newer adapter on-board BIOS 
versions support booting from CD-ROM drives as well. 

OPERATING-SYSTEM Capacity Limitations 

IBM and M$ officially say that DOS 5 and later versions 
will support up to eight physical hard disks.  IBM says 
that OS/2 1.30.1 and later versions (including 2.x) support 
up to 24 physical hard disks, and because OS/2 includes 
DOS, that implies that DOS under OS/2 would support 24 
physical drives as well.  

(Since I have never installed over four disks of any kind 
on my computers,  and since DOS, OS2, and Windoze all 
number the hard disks, CD's, tape drives automatically,  
the only time I could see you needing to identify a disk 
manually would be when   using ASSIGN to give a disk 
or folder a specific ID.  Then that would be Nullified next 
time you rebooted(?).  All my networking and DOS classes 
seem to be rooted in this same concept, ie" last drive=Z. ) 

When DOS boots it automatically assigns C: to the first 
primary  partition on the first hard disk and then assigns 
D:, E:, etc.. to all the primary partitions it finds and then 
assigns the remaining Alpha ID's to the logical partions 
on all extended partitions.  After that it assigns all the 
removable drives and CD ROM drives.  

So what happens when it hits 24?  ANYONE?? 
If SCSI  can can have 28 drives how are they numbered?  

If the Enhanced BIOS allows up to 128 drives How Are They 
Numbered,  or is that just for UNIX and LINUX, where they list 
all drives individually by NUMBER and type.  

Personally, I see no use for so many drives/devices except in 
a network server, and then it would have to have a pretty big ,
fast CPU, or 2/4/6/9 CPU's, and 500+ MGB fast memory just to 
keep track of it all.

BOB 'DOMAN' MOSS "I know nothing, Colonel Klink" 
  
On Fri, 16 Feb 2001 18:32:29 +1100 "da Silva, Joe"
<Joe DOT daSilva AT emailmetering DOT com> writes:
> Oh, yeah - that reminds me ... does anyone know for
> certain that this 24 drive limit is real, or are people
> simply assuming this because there are about 24
> letters (26 actually) in the English alphabet?
> 
> I remember reading an old Micro$oft manual that
> said you could have *more* drive letters than there
> were letters in the alphabet, so that the drives above
> "Z:" would be "[:" and so on, as per the ASCII
> character set ...
> 
> Joe.
> 
> Speaking of other (possible) myths, I also vaguely
> recall reading somewhere that the often quoted
> statement, that "if you have two drives on an IDE
> cable, then the slowest drive will determine the
> speed (transfer rate) of both drives", is a myth ...
> 
> > -----Original Message-----
> > From:	Bernie [SMTP:bernie AT mbox302 DOT swipnet DOT se]
> > Sent:	Friday, 16 February 2001 17:46
> > To:	opendos AT delorie DOT com
> > Subject:	Re: Hard Disk 20gb and dos
> > 
> > Pat wrote:
> > >Yes the is very true. DOS only has the cpability of 24 total 
> drives,
> > >whether they be physical or logical or a conbination of both. So 
> why use
> > >an 8GB drive for FAT 16? Really seems rediculous to me.
> > 
> > I know that, still I have more than 10GB for DOS (MS-DOS 6.2, two 
> drives)
> > here. I have no idea what it is. My hope is that sometime this 
> week (ie.
> > tommorow) or the next I'll get my new parts. With a new 46.1GB HD 
> I'll
> > start over with a fresh set of GBs - not even copying the c:\dos 
> directory
> > :)
> > //Bernie

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