[Gllug] Beagle Board

Andrew Farnsworth farnsaw at stonedoor.com
Mon Jan 12 17:48:21 UTC 2009

In their defense, early PC Hardware did not include the necessary circuitry to
permit preemptive multitasking.  Cooperative multitasking does have the advantage
of being able to more efficiently utilize the hardware provided the programmer
which wrote the code correctly designs the system to efficiently handle this. 
Sadly, this was seldom the case, and as such preemptive multitasking was/is a
much better model.  Apple got around most of this by embedding a systemclick (a
context switch to allow another process to take it's turn on the CPU) into almost
every system call provided by the OS.  This made most programs very simple to
write and performed much like preemptive multitasking.  Photoshop was a notable
exception because it would process a substantial part of an image before doing
either a system call or an explicit systemclick.

Ah the good old days... :-)


On Mon Jan 12 12:38 , Peter Corlett <abuse at cabal.org.uk> sent:

>On 12 Jan 2009, at 16:46, John Edwards wrote:
>> RISC OS was release in the late 1980s. Both MacOS and Windows
>> were using co-operative multitasking at that time (and for
>> years afterwards).
>Windows NT was a fully pre-emptively multitasked, multiuser system  
>with virtual memory and protection between processes back in 1993;  
>MacOS appears to have followed in around 1999 with Rhapsody. The  
>reasonably useful consumer equivalents would be Windows 2000 in 2000,  
>and MacOS X.1 in 2001. These all offered a reasonable amount of  
>backwards compatibility with their earlier more unreliable releases.
>Remind me again, what date did Acorn release *their* pre-emptively  
>multitasked, multiuser system with virtual memory and protection  
>between processes?
>And let's not forget the Amiga, which had pre-emptive multitasking  
>right from the start in 1985. Oh, hang on, everybody did. It fell by  
>the wayside just like RiscOS because it failed to keep up people's  
>expectations of what a modern operating system should do.

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