[CST-2] Comp. Sys. Modelling

[Alvin]

> CSM - 2000P9Q7
>=20
> Has anyone done this. If so...I have a couple of queries...
>=20
> Second part - can we give a numerical value to this? Since the bounds of
> a balanced machine depend on utility, which depends the number of
> customers, then I can only give a formula answer of 10N/(3+N) &
> 40N/(3+N) as the bounds...

The first bound provided by giving all devices Dav, so the max throughput i=
s
1/Dav =3D around 18.6 transactions/s

The second provided by giving as many devices Dmax as possible, so the max
throughput is 1/Dmax =3D 10 transactions/s
=20
> Third part - first of all, I'm assuming the formula on the paper is
> wrong and it's actually X(N) =3D N/(N+K-1) x 1/Di like the notes, not with
> the plus sign like on the paper... - what value of demand do we use to
> get the 'expected value'. If it's Dmax (i.e. 0.1 s for Disk 2 from part
> (2)) which means 7 users in the system at any one time. Or alternatively
> Dav (which I get as 0.05375 s from averaging all the D values) I get
> 1.81. Which is the right one to pick? I assumed Dav but then it's later
> given in the notes as an 'optimistic' bound, and I suppose I have to
> consider the system bottleneck...or I might be utterly wrong...

Just give it as lower bound < N < Upperbound

> Oh, and does anyone know where to get decent coffee this time of
> night...I'm all out, and the usual places are shut. =A6-O

24 hour garage.

Alvin