[brk]

My father (and I for a bit) worked in IBM field service. The answer is all of the above. You’d carry some common things with you, but most parts needed were picked up at local parts depots that IBM stocked.

For larger clients (like the K Mart stores) we had private pilots on call that could be sent to another city to get a ~$500 part. Especially during holiday shopping season. Some clients had onsite spares but that wasn’t very common. They relied on IBM service to just handle everything. For some customers we had a 2 hour on-site SLA.