Re: The Nature Of Operating Systems :-) (Was: Re: Linux Beer Hike)

["Robert Speed" <nospam [at] Viclabs.co.uk>]

On 11 Apr 00, at 23:18, Alex Hudson wrote:
> interface. No apps. A better comparison would probably be Acorns....

Yay to the man at the front before I said it !!!
BTW - RISCOS fits a full GUI, font manager, 6 fonts (in ROM) etc 
into 4MB.
But then I still feel it has the best font manager (the anti aliasing to 
simply super) on the planet - not much else in keeping up to date, 
(like there's no vm support, no SMP, not really much in the way of 
privilege levels in the kernel and its not portable whatsoever), but 
hey, that's what Linux and BSD are there for!

> > AFAIK a RISC kernel would probably be larger too...

ARM code is remarkably compact - without going into Thumb 
extensions (16 bit instructions when stored - uncompressed on the 
fly), I find that some things compile to be a larger binary, others are 
smaller.
Generally they're a similar sort of size.
However, the barrel shifter (performing logical operations in the 
same instruction as another - ie.
ADD R0,R1,LSL #2 will add the contents of R1 to R0 and logically 
shift left(by 2 bits (multiply by 4) the result) all in one operation 
(generally 1 clock cycle))
and the ability to conditionally execute instructions (adding EQ to 
the mnemonic stub will only execute it if the Z flag is set (the last 
compare was equal)) certainly helps keep code density down to 
respectable levels.
(There's even an NV (NEver execute) condition - not entirely sure 
why, but it's there all the same...)

I'll do some size comparisons for kernels for ARM/x86 when I get 
home.
Does anyone have an iMac (& they're using Linux!) so I can see 
how the PPC fairs ?

> 
> Yep, but not a great deal though. Possibly would need some FPU emulation,
> depending on the architecture. The CISC->RISC instruction growth wouldn't be
> vast, I shouldn't expect.
Yeah, FPUs were never really much of a concern when the ARM 
was originally drawn up - the design goal was really for efficiency in 
execution and die size, complexity.
It's really been something I've missed (never having bought the FPU 
co-pro) when compared to the x86 and 68k worlds.


Right, I'm rambling so I'm off...


Rob S.
Vickers (Laboratories) Ltd.
Grangefield Industrial Estate, Pudsey, Leeds LS28 6QW
Switchboard: +44 (0)113 236 2811   Fax: +44 (0)113 236 2703

All opinions are my own and ! Vickers.
The nice thing about Windows is that it doesn't just crash.
It displays a dialogue box and lets you click OK first.
---------------------------------------------------------------------
Sheffield Linux User's Group - http://www.sheflug.co.uk
To unsubscribe from this list send mail to
- <sheflug-request [at] vuw.ac.nz> - with the word 
 "unsubscribe" in the body of the message. 

  GNU the choice of a complete generation.