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