Mainframes combined most of the muscle in centralized location for weaker, thin clients (eg terminals) to use remotely. Alleged security and efficiency benefits of centralization with one set of staff handling issues for third parties. The CPU, memory, and I/O was metered with many locations charging departments per use. Used VM/370 to virtualize OS's that could run in parallel for various workloads. Scale up quickly. Later clustering and Sysplex for high availability with multiple datacenters. Specialist packages (aka platforms) for various languages or use cases. Hardware accelerators for I/O, databases, crypto, and so on.

Was I just reading a list of benefits and features of modern clouds? Young folks would think so but that was all mainframe stuff from 1960's to 1980's with key hardware & VM tech done by early to mid 70's.