5.3 on Intel 386 ?

[Erik Trulsson]

On Thu, Nov 25, 2004 at 05:20:02PM +0900, Rob wrote:
> Scott Long wrote:
> >Rob wrote:
> >
> >>Wilko Bulte wrote:
> >>
> >>>On Thu, Nov 25, 2004 at 04:02:28PM +0900, Rob wrote..
> >>>
> >>>>Hi,
> >>>>
> >>>>I thought 386 support had been removed since 5.X. But
> >>>>http://www.freebsd.org/releases/5.3R/installation-i386.html
> >>>>says:
> >>>>
> >>>> 1.2 Hardware Requirements
> >>>> FreeBSD for the i386 requires a 486 or better processor to install
> >>>> and run (although FreeBSD can run on 386 processors with a custom
> >>>> kernel)....
> >>>>
> >>>>What does this mean?
> >>>
> >>>
> >>>
> >>>One thing you need on the target system (IIRC..) is a FPU. 
> >>
> >>
> >>
> >>So?
> >>The hardware requirements state "FreeBSD can run on 386 processors...".
> >
> >
> >The GENERIC kernel that is shipped with FreeBSD will not boot on an 
> >80386 processor, period.
> >
> >>Can I induce an FPU into my system by customizing my kernel?
> >
> >
> >You'll need an FPU and a custom kernel that is compiled with the
> >CPU_I386 option.
> 
> I'm not an expert here, but I found this:
> 
>    80386SX = 386 w/o FPU
>    80386DX = 386 w/ FPU

That is wrong. Neither the 80386SX nor the 80386DX have an FPU.
The difference between them is that while the DX has a full 32-bit
databus and addressbus, the SX only has a 16-bit databus and a 24-bit
databus. This difference is not visible to the programmer but only to
the hardware designer, i.e. all programs that run on an 80386DX will run
on an 80386SX as well.
For both of them you can add an external FPU (80387DX/80387SX)

You might have been thinking of the 80486 where it is indeed the case
that
  80486SX = 486 w/o FPU
  80486DX = 486 w/  FPU
If you have an 80486SX you can add an 80487SX to get an FPU.
FreeBSD 5.3 requires an hardware FPU to run.


> 
> Should instead, the "Hardware Requirements" for 5.3 then mention
> this:
> 
>   ...(although FreeBSD can run on 80386DX processors...
> 
> to be more precise, to avoid confusion/frustration for 80386SX
> owners?

No.  FreeBSD 5.3 should be able to run on both 80386DX and 80386SX
processors *IF* you have an external FPU.  You will also need a
custom-compiled kernel with support for 80386. (The default GENERIC
kernel has 80386 support disabled since having it enabled makes it run
slower on more modern processors. 


-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at student.uu.se