Date   : Fri, 30 Dec 2011 06:13:21 +0100
From   : rick@... (Rick Murray)
Subject: About ARM PC

On 29/12/2011 14:13, Daniel Alejandro Benavides D. wrote:

> well, I kind of say the GNU/Linux is not the worst system,

No, but then with its heritage as a secure and capable server platform, 
is it really the best option for small embedded devices?


> (I miss the times when you boot up the kernel with a Floppy disk image).

I don't. It was *slow*!


> Anyway the new OSes coming from software providers will run above an
> Micro-Kernel?

No, the OS and the microkernel are intertwined. Really, all the 
microkernel is, in reality, is an attempt to take all the device drivers 
and crap that bloated the traditional (monolithic) kernel and push them 
into user space as applications. This means the kernel can get on with 
being a kernel, and the drivers etc can be developed away from the 
kernel. One could argue that RISC OS itself is a sort of microkernel 
concept - after all, you *can* load arbitrary filesystems (IDEFS, 
SCSIFS, etc) and such. It fails in reality as there is a lot of rubbish 
(keyboard, audio, video, timers, etc) that doesn't belong in a microkernel.

Jury is still out on whether or not a microkernel really offers that 
much in the way of benefits.


> There are some intents to hand-craft Linux to a kind of Micro-kernel
> where you can run anything like that, you know, RISC OS, etc.

The only worthwhile Linux microkernel system I'm aware of is Minix. It 
isn't really Linux compatible. I'm not even sure if it has been ported 
to anything other than x86 hardware.

You pretty much *cannot* run one OS on top of another OSs kernel. I'll 
give you two examples:

   1. RISC OS on top of a Linux-like microkernel
      Q: How, then, do you propose to handle RISC OS's heavy use of SWIs?

   2. Linux-like on top of a RISC OS anything
      Q: How would you implement fork() ?

The kernel (monolithic, micro, or otherwise) is responsible for the 
"personality" of the machine. At its heart, it manages memory and 
processes and passes messages between these processes. How it does all 
of this has a big impact on the behaviour of the OS.

RISC OS, however, is a special case, what with it managing very little 
beyond the basics to get the system running. Memory (paged, as opposed 
to "a big wodge") and process management and message passing are all 
handled by WindowManager. It's a bit like Windows 3 loading on top of 
DOS (but, then, Windows subsequently replaced a lot of DOS as it did 
so). You could be forgiven for asking what exactly the RISC OS kernel 
*is*. We might have one-and-a-half, depending on how you define it.


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...