What is an Operating System?
1. Referee
– Manage sharing of resources, Protection, Isolation
» Resource allocation, isolation, communication
2. Illusionist
– Provide clean, easy to use abstractions of physical resources
» Infinite memory, dedicated machine
» Higher level objects: files, users, messages
» Masking limitations, virtualization
3. Glue
– Common services
» Storage, Window system, Networking
» Sharing, Authorization
»Look and feel
Four fundamental OS concepts
1. Thread
– Single unique execution context
– Program Counter, Registers, Execution Flags, Stack
2. Address Space w/ Translation
– Programs execute in an address space that is distinct from the memory space of the physical machine
3. Process
– An instance of an executing program is a process consisting of an address space and one or more threads of control
4. Dual Mode operation/Protection
– Only the “system” has the ability to access certain resources
– The OS and the hardware are protected from user programs and user programs are isolated from one another by controlling the translation from program virtual addresses to machine physical addresses
ps: difference between threads 与 processes
- process encapsulate one or more threads sharing process resources
- Processes provides memory protection, threads more efficient than processes
Some other BIG OS Concepts
• Interrupt handlers (including syscall and trap)
• File System
– Integrates processes, users, cwd, protection
• Key Layers: OS Lib, Syscall, Subsystem, Driver
– User handler on OS descriptors
• Process control
– fork, wait, signal, exec
• Communication through sockets
• Client-Server Protocol