[unios] Re: Ladder?

[Anders Petersson]

From: Anders Petersson <anders.petersson@mbox320.swipnet.se>

At 1998-12-25 , you wrote:
>From: Tril <dem@tunes.org>
>
>On Fri, 25 Dec 1998, Srikant Sharma (Chiku) wrote:
>
>> From: "Srikant Sharma (Chiku)" <srikants@wipinfo.soft.net>
>> 
>> I have discussed about the ladder model in an article written by me.
>> "OS development requirements".  You can find it at the UniOs page.
>> The model is described in last paragraphs.
>
>Thanks! I'll paste it here and reply to it.
>
>> The Ladder Model 
>
>> An OS project needs These three (Loader, Kernel, bare minimum utils) 
>> components to be decided upon first. The decision requires a lot of
>> consideration such as what entry point the kernel is going to provide,
>> What kind of devices/hardware it's going to deal with etc.  These
>> decisions are 'highly' influenced by the nature of utilities which we
>> want to provide. But one can clearly see an interdependency. One should
>> not decide upon a very complex outer design which demands a high level
>> of complexity in the kernel. 
>
>Why can't we have a complex outer design?  Because in this model, the
>kernel is the bottleneck and must be restricted to ensure performance.
>Therefore all the rest of the system gets restricted, just so the kernel
>won't run too slow.  But why have the bottleneck in the first place?  I
>think the centralized design of current systems is one of the main reasons
>they are inflexible.

Yes, a decentralized system is the future. Microkernel, nanokernel or
no-kernel... that's the question.

>> The basic idea is to start with a modest
>> utility frame work and actually build a prototype/working kernel
>> required for this. Then slowly increase the complexity of the utilities
>> while enhancing the kernel. This can be termed as the 'Ladder' model of
>> development where two interdependent goals proceed parallely
>> supplementing each other's requirements. 
>
>Working on several components in parallel is ok.  
>
>The order to construct the system is OK too.  But only if the system is
>already designed.  It would be bad to try a ladder development if we
>didn't know the final result.  I would rather call this a "ladder
>implementation style" than "ladder development" because it needs to be
>very clear that the ladder is not part of the design phase.  In my
>experience in TUNES, the design is integrated and can only be developed
>non-linearly (it requires thinking around in circles many times to develop
>the concepts).  UniOS is so much like TUNES you probably will design it
>non-linearly, too.

A system like UniOS (or again maybe mOS) where everything is so
interrelated must necessarily be *designed* non-linearly.

When it comes to the implementation, I guess we'd be fine off first
implementing everything needed in a simple manner and then come back
afterwards to improve each part.

binEng



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