From: wes.parish@paradise.net.nz (Wesley Parish)
Subject: [TUHS] Redoing "V6on286" or porting V7...?
Date: Mon, 14 Nov 2005 22:38:31 +1300 [thread overview]
Message-ID: <200511142238.31662.wes.parish@paradise.net.nz> (raw)
In-Reply-To: <20051113201609.GW6574@gsmx07.alcatel.com.au>
On Mon, 14 Nov 2005 09:16, Peter Jeremy wrote:
> I've also looked at this in the past. I lost interest when my
> intended target box died (and I realised I didn't have the free time).
>
> On 2005-Nov-12 08:18:50 -0500, Brantley Coile <brantley at coraid.com> wrote:
> >i may be wrong, but i don't think you want the segments. pdp-11
> >segments divided the address space into eight, well, segments. each
> >could be grow up or grow down and had a physical base and a limit.
> >intel segments don't work that way. the major difference is that the
> >segment selector, instead of being the upper most three bits of the
> >virtual address, is not even in the address space at all.
>
> Actually the 286 MMU is very primitive compared to the PDP-11. One
> crucial difference is that Unix has the implicit assumption that the
> stack is in the data space - which is not true on the 286. This
> difference is fairly critical to Unix and makes it impossible to
> accurately reproduce the traditional Unix memory protection.
>
> >so the eight, for a pdp-11/40 say, or the sixteen for the 11/70 don't
> >really apply. instead just give each data segment the whole 64k
> >address space and it'll not klobber anybody else. just itself.
>
> This is fairly wasteful of RAM. Keep in mind that V6 cannot page -
> a process is either entirely in memory or entirely on disk. If you
> limit yourself to 640K RAM, you are probably restricting yourself
> to about 6 resident processes. And swapping means moving 64K of
> data to/from disk.
>
> This approach also makes brk(2) a no-op. There's nothing to prevent a
> process using as much heap as it wants (or crashing into the stack).
> (No SIGSEGV or SIGBUS errors).
>
> >you're correct to imply that v6 takes up MUCH less space than other
> >systems. it's amazing how small you can run this. the root in the
> >6th edition system is only 1.4MB. and that includes the normal
> >binaries, libraries and the source to the kernel. it'll run great on
> >a floopy.
>
> You will need to have a swap partition. And if each process has a
> 64K data segment, you'll need a comparatively large amount of swap.
> The biggest disadvantage of a floppy will be performance - latency
> of about 80msec, I/O of about 40KB/sec.
>
> Have you identified a suitable C compiler? There aren't many open
> source 16-bit x86 compilers, especially ones that can run in 16-bit
> mode. None of the ones I found generated particularly good code.
> This may impact you ability to get the larger utilities (and maybe
> the kernel) to fit into 64K I-space.
Would it be possible to use some of the DOS ones? At least to bootstrap a
more true-to-Unix one?
I'm thinking of the likes of bcc, available plus source at the FreeDOS web
archive. Or OpenWatcom's DOS 16-bit.
Wesley Parish
--
Clinersterton beademung, with all of love - RIP James Blish
-----
Mau e ki, he aha te mea nui?
You ask, what is the most important thing?
Maku e ki, he tangata, he tangata, he tangata.
I reply, it is people, it is people, it is people.
next prev parent reply other threads:[~2005-11-14 9:38 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-09 17:26 Lyrical Nanoha
2005-11-09 21:54 ` M. Warner Losh
2005-11-09 22:03 ` Brantley Coile
2005-11-12 6:13 ` Albert Cahalan
2005-11-12 13:18 ` Brantley Coile
2005-11-13 20:16 ` Peter Jeremy
2005-11-14 9:38 ` Wesley Parish [this message]
2005-11-14 15:45 ` Brantley Coile
[not found] ` <8a61b612cf43394f33e6531339fe4263@coraid.com>
2005-11-14 19:49 ` Peter Jeremy
2005-11-14 20:31 ` Brantley Coile
2005-11-16 21:41 ` Lyrical Nanoha
[not found] ` <17277.62390.986234.433543@hod.localdomain>
2005-11-18 17:59 ` Lyrical Nanoha
2005-11-19 4:17 ` Brantley Coile
2005-11-15 3:08 ` Greg Haerr
2005-11-15 3:40 ` Peter Jeremy
2005-11-15 13:30 ` Brantley Coile
2005-11-14 21:34 Norman Wilson
2005-11-14 22:59 ` Brantley Coile
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=200511142238.31662.wes.parish@paradise.net.nz \
--to=wes.parish@paradise.net.nz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).