z/OS Summary

z/OS is the computer operating system for IBM's zSeries line of large mainframe servers. This is a small summary of my limited knowledge of the z/OS operating system.

Lineage

1. MVS - The original mainframe OS
2. OS/390 = MVS + USS (Unix System Services)
3. z/OS = OS/390 + 64bit zSeries processors

What I think I know

Each zSeries machine can be split into LPARs (logical partitions). Each LPAR runs its own operating system (e.g. Linux (zLinux), OS/390) and shares the system resources (e.g. memory, DASD, cpu) with other LPARs. The LPARs can communicate with each other via hipersockets. LPARs running on a machine have access to a configurable amount of engines but can be throttled by a configurable percentage share of the resources. LPARs are managed/clustered by a sysplex which allows the LPARs on a single machine to share resources.

DASD - a fancy mainframe term for a hard drive.

CPU sharing - One of the coolest things about the mainframe is its ability to share system resources.. For example, an LPAR (P390) has access to 11 of the 12 processors (rated at 345 MIPS) on a zSeries machine and has an 80% share of the resource. This translates to 9.6 processors and 3,312 MIPS. If the other LPARs on the footprint are not requesting their share, P390 can consume up to 3,795 MIPS (or 92% of the installed capacity, all 11 processors).