Provides Abstractions Hardware has low-level physical resources with complicated, idiosyncratic interfaces. OS provides abstractions that present clean interfaces. Goal: make computer easier to use. Examples: Processes, Unbounded Memory, Files, Synchronization and Communication Mechanisms.
Provides Standard Interface Goal: portability. UNIX runs on many very different computer systems. To a first approximation can port programs across systems with little effort.
Mediates Resource Usage Goal: allow multiple users to share resources fairly, efficiently, safely and securely. Examples:
- Multiple processes share one processor. (preemptable resource)
- Multiple programs share one physical memory (preemptable resource).
- Multiple users and files share one disk. (non-preemptable resource)
- Multiple programs share a given amount of disk and network bandwidth (preemptable resource).
Consumes Resources Solaris takes up about 8Mbytes physical memory (or about $400).
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