[echo]

hi everyone,
i used to use sgi's from about 1999 - 2003 at a school. they had indigo2's, o2's, octanes.
i want to get one soon for nostalgia, probably an octane of some sort. i only know a little bit about them.
i have some questions.

can all the machines run all the same software, or does changes in the CPU or video systems prevent it?
for example, i wanted to try running the oldest versions of alias and wavefront, from before the companies merged.
how far back can you run a software with each machine/configuration? there was sgi software in the 1980s too, right?

from just looking at a machine, is there a way to determine what speed cpu is in it? part# on the cpu/heatsink itself anywhere?
i know sometimes the chassis sticker says a cpu speed, but some don't, and it could have been changed over the years.
i assume the video boards all have a part number on them, on the edge of the board?

is there a way to decipher the meaning of the system barcode? it's a sticker on the rear, below the fan & above pci card-cage.
the barcode looks like this: 08006912632E
this barcode belongs to a model# CMNB015ANG300
i assume the system barcode tells what the configuration of the machine originally was.

there are also barcode stickers indicating when a cpu upgrade was performed, can those codes be understood?

what does the octane front-plane do? what does it look like?
from just looking, how can i check what revision of front-plane it is?

thanks!