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From: zt0009%DMSWWU1C.BITNET@cunyvm.cuny.edu (Kai Henningsen)
Newsgroups: comp.os.minix
Subject: Re: PC MINIX ==> MINIX/386SX
Message-ID: <18772@nigel.udel.EDU>
Date: 7 May 90 19:44:22 GMT
Sender: mmdf@udel.EDU
Lines: 42

> Since it is agreed that MINIX/PC is a toy mainly due to the process space
> limit, a new hardware baseline is needed to put INTEL-MINIX on.
> Since PC's are being replaced by AT's and - much quicker - AT's will
> disappear and be replaced by 386SX machines - MINIX should be ported to
> the 386SX quickly.

Exactly.

> I don't like INTEL processors (I am 68000-Fan), but at the moment 386SX
> machines provide most power at a meanwhile moderate price. Once a true
> 32-bit compiler/assembler for the 386 is ready, I think the MINIX-ST
> implementation is the starting point to choose:
>
> As a first step, map a single 32-bit address space shared by all processes
> - this is the situation on the 68000 so we need shadowing - and, when this
> runs, exploit the MMU for relocation and protection.
>
> It is my opinion that it makes no sense porting PC-MINIX to 80286 protected
> mode. It is better to go to the 80386 - 80x286 is brain-damaged for x<3.

You are quite right re: brain damaged. However, let me point out that a
better way would be a mixture of the current ST and PC versions, that is,
keep the PCs segments (thus getting a separate adress space for every process),
but make those segments (that is, 1 Code & 1 Data segment) LARGE (i.e. 32 Bit).
I think that the 286 version already includes everything interesting re: this.

In a later step, introduce paging. To prepare for this in advance, consider
allocating all memory in 4K chunks which can later be pages (that is, make
a click be 4KB).

> Though I am not an expert in INTEL processors, I feel that all the 386 work
> carried out at the moment should converge somehow, and that it is time to
> cut a clear line between 80386 MINIX and PC/AT MINIX.

Agreed completely. Do NOT include a compatibility mode; since we have all the
sources, there is no need for binary compatibility (which does not exist with
other versions of MINIX either).

> Christoph van Wuellen.

Kai Henningsen
zt0009 @ dmswwu1c . bitnet