Path: utzoo!mnetor!uunet!husc6!bbn!mit-eddie!uw-beaver!tektronix!reed!percival!bucket!leonard
From: leonard@bucket.UUCP (Leonard Erickson)
Newsgroups: comp.sys.ibm.pc
Subject: Re: DOS upgrade and SYS
Message-ID: <865@bucket.UUCP>
Date: 26 Apr 88 07:02:34 GMT
References: <3689@sdcc6.ucsd.EDU>
Reply-To: leonard@bucket.UUCP (Leonard Erickson)
Organization: Rick's Home Grown Unix; Portland, OR
Lines: 32
Keywords: MS-DOS SYS

In article <3689@sdcc6.ucsd.EDU> ir230@sdcc6.ucsd.EDU (john wavrik) writes:
<  I'm curious as to what SYS does other than what I tried to do by hand. Isn't 
<  the DOS determined (internally) by the two hidden IBMxxx.COM files and 
<  COMMAND.COM? It's obvious that SYS is quicker -- but why is it essential?  Is 
<  there something that Peter Norton didn't tell me?  As a further (potential) 
<  problem, I find that the manual says that SYS will not work if the new system 
<  is bigger than the old. What happens if I want to install DOS 3.3, rather than 
<  just an upgrade of DOS 3.2, on a hard disk full of files? 

At boot time, the ROM bios loads the BIOS and DOS from the boot disk. Until they
are loaded, the directory isn't readable (as they contain the code to read it!). 
So the ROM BIOS has to be able to find those two files. The simplest, most
reliable method is to have the boot sector tell where they start (right after
the FAT and root directory) and have thenm in ONE CONTIGOUS BLOCK following
this point.

So when you copied the files, they went into the first free clusters on the HD
and *then* the clusters used by the old copies went away. SYS copies them on
top of the old files and in a contigous block as well. 

The need for the clusters to be contigous explains why sysing a larger system
won't work. With a bit of work it is possible to remove the files (or worse
yet directories) that are occupying the needed space. The only time I've had
to deal with this, I did a SYS and then removed the hidden and system
attributes. I then used a disk optimizer (yes, I *know* this is a kludge!).
Then I set the bits back. It worked. Your mileage may vary....

-- 
Leonard Erickson		...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I used to be a hacker. Now I'm a 'microcomputer specialist'.
You know... I'd rather be a hacker."