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Old 25 March 2015, 19:05   #40
Mrs Beanbag
Glastonbridge Software
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Join Date: Jan 2012
Location: Edinburgh/Scotland
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Originally Posted by idrougge View Post
Protect already has a USER flag for that purpose, but mainstream filesystems don't support it. I think it came into being as part of Envoy.
i don't see it in any docs, unless i'm missing something

I use my Mac as a single user. In case I need to alter a protected file, the system asks for my password. It could just as well ask for a password without being multi-user.
I use Linux this way as well, in fact as i already said, Ubuntu-family of Linux no longer provides a root user that you can log in as. But when you put your password in, on Ubuntu or Mac, you become "superuser" and get the access rights of the root account. It doesn't really matter to the computer if the superuser and the normal user are the same person or not, behind the scenes that is what is going on. The term "multiuser" is really a piece of history because that was the context in which the technology was originally devised, the important separation here is really not between "user" and "user" but between "user" and "root" which was always kind of special, you have "root" and then you have "user accounts" on another level.

You are correct in that purely for security we don't need multiple directories in the home drive that different individuals can access, but if you can have even one such directory you can have any number of them. Security with only one user is equivalent to using only a single bit to store the user IDs.

I was looking at the 68020 manual and the A1200 specs and one thing i noted is that it is possible to determine if the CPU is running in supervisor or user mode from the outside. This is output on the CPU's FC0-2 pins. FC0 and FC1 are connected to AA Gayle but sadly FC2 is needed to differentiate supervisor from user access, although it can tell the difference between data and instruction accesses. I don't know for what it uses this information.

Also i don't know exactly how the CPU drives the IDE interface. It goes through Gayle somehow but whether it is just a set of memory-mapped registers like for the floppy drive, or some other mechanism i don't know. It's possible it does it through the privileged MOVEC and MOVES commands, in which case things are looking up.

Last edited by Mrs Beanbag; 25 March 2015 at 19:14.
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