UNIX hardware sizing for multiple instances

My group has requirement to run three, possibly four, instances of Oracle (8.1.7, most likely) on a UNIX server
(AIX, if that matters). We are considering separate instances
because the software comes from three different vendors. The fourth database will be ours and may be able to run on one of the other three instances.

For determining the size of the server we are using the following guidelines:

disk space = amount needed for the o/s (including virtual memory) +

             Oracle software +
             data files

physical memory = amount needed for the o/s +
                  total sizes of the SGA for all instances

number of processors = at least two

processor speed = somewhere in the middle range

We are assuming that the processors do not have to be blindingly fast for a database server. We are also assuming that the number of processors is more important than their speed.

So my questions are:

1. Are we on the right track with the physical memory calculation?
2. Should we figure in an additional amount of memory for each dedicated server process, assuming that we will not be using MTS?
3. What criteria should we use to determine number of processors?
4. Any other comments about our calculations and assumptions?

Thanks,

Peter Schauss
Northrop Grumman Corporation
516-346-3148
schaupe_at_mail.northgrum.com

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Schauss, Peter
  INET: SCHAUPE_at_mail.northgrum.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L


(or the name of mailing list you want to be removed from).  You may

also send the HELP command for other information (like subscribing).