JDM.... IMHO there's a lot of "business" issues to deal with before you tackle the "technical" issues. For example:
- mission critical on a single machine ? (doesn't sound too mission critical to me)
- feeding a car assembly line (that does sound mission critical)
- what budget is available ?
- what's the cost to your business if that Model 150 ever goes "off the air" (i.e. stops the assembly line) ? $50,000 / hour ? $250,000 / day ? (pick a number)
Regardless, everyone's situation is different. What works for one, may not work for another.
With respect to your questions:
- if your environment really is mission critical, then I'd consider something that keeps your car assembly line going, above all else. Redundant systems come to mind. Upgrade ? may be, may not, it depends. Migrating to a pair of p5 processors, now, may provide you with more options.
- run the command --> bootinfo -p <-- on your 150, If it responds with "chrp", it will run AIX 5.3. I seem to recall a 150 will in fact run AIX 5.3 but run the "bootinfo -p" command to confirm this for yourself. AIX 5.3 also has other "minimum" reqm'ts that might bite you on a Model 150, like 128MB memory & something like 2-3 GB free space. If you're using a single 4.5 GB drive that might be an issue for you. Remember these are minimums, not recommended values.
- the Model 150 is a 32 bit machine, so the AIX 5.3 kernel will need to be the 32 bit version (not the default 64 bit kernel)..... this is not a problem, IBM provides both. But AIX 5.3 is the last announced version that will support a 32 bit kernel. AIX 5.4 allegedly is 64 bit kernel only, so it's pretty easy to conclude that AIX 5.3 will be the last release that will run on a Model 150.
Good luck sorting thru all the pros & cons. You've only scratched the surface.