[unios] Re: Ladder?

[Tril]

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.

> 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.

David Manifold <dem@tunes.org>
This message is placed in the public domain.


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