Winter 2002 1

CMPE 155

Week 2

Winter 2002 2

Review?

Computers Operating Systems Kernels Distributed Systems

Winter 2002 3

Computer

“Hardware”. Processor(s), main memory, disk(s),

keyboard, display(s), network interface, other I/O devices.

Winter 2002 4

Multiple Processor Systems (1)

“Tightly-coupled”– Shared-memory muliprocessor

P ……

Shared Memory

Winter 2002 5

Multiple Processor Systems (2)

“Less tightly-coupled”– Message-passing multicomputer

P ……M

PM

PM

PM

Winter 2002 6

Multiple Processor Systems (3)

“Loosely-coupled”– Distributed systems”

Network

Computer

ComputerComputer

Computer

Winter 2002 7

What is an OS?

Machine/resource manager.

Physical Devices

MicroarchitectureInstruction Set Architecture

Operating System

Compilers, Editors, etc.

Hardware

Application programs

Winter 2002 8

OS as extended machine…

Top-down view. Layer of software that hides hardware. Provides programmer easier instructions.

– E.g., read block from file.

(Part of) the OS runs in supervisor (privileged) mode: can execute priviledged instructions (e.g., access to physical decices through drivers).

Winter 2002 9

OS as resource manager

Bottom-up view. Provides orderly and controlled

allocation of resources. Provides (“concurrent”) programs (fair)

access to resources (processor, disk, printer).

Time (e.g., CPU) and space (e.g., memory) multiplexing.

Winter 2002 10

OS History

Winter 2002 11

First generation: 1945-1955 Vacuum tubes: machines took whole

rooms! Machine language programming

(plugboard wiring). No OS.

Winter 2002 12

Second generation: 1955-1965 Transistors made computers

commercially viable. Builders, operators, users. Mainframes: multimillion dollar

machines. Punch cards, input and output tapes. Batch systems.

Winter 2002 13

Third generation: 1965-1980 ICs. Multiprogramming.

– Machine shared by “concurrent” programs.– Memory partitions hold multiple jobs.

Timesharing.– Multiprogramming still batch processing: scientific

computation and commercial data processing.– Cheap terminals: interactive use.– Interactive service + batch processing.

Winter 2002 14

Fourth generation: 1980-… High-scale circuit integration. Computer miniaturization. Mainframes -> minicomputers ->

microcomputers or PCs. PC OSs: CP/M, DOS, MS-DOS. GUI-based OSs: UNIX-based, MS

Windows-based, MAC OS, …

Winter 2002 15

Modern OSs Mainframe OSs: IBM’s OS/390, DEC’s

VMS. Server OSs: Solaris, FreeBSD, etc. PC OS: Linux, MacOS, Windows… Real-time OSs: VxWorks. Embedded OSs: Linux, PalmOS,

Windows CE Smart card OSs

Winter 2002 16

Basic OS Concepts

Winter 2002 17

Processes

Process: program in execution.– Address space: memory usable by

program (text, data, stack).– State: registers.

OS uses process table to keep track of processes.

Processes can create other (child) processes.

Winter 2002 18

Inter-Process Communication (IPC) Shared memory.

– Processes communicate/synchronize through a shared data item.

Message passing.– Processes communicate via messages.

Winter 2002 19

Shared Memory

Processes must access shared data in a mutual exclusive way.

Primitives:– Semaphores: Dijkstra(1965)

• P(S) and V(S) operations.• Atomic (indivisible) operations.

– (Conditional) Critical Regions– Monitors

Winter 2002 20

Message Passing

Processes communicate/synchronize by sending/receiving messages.

Primitives:– Send(message), receive(message).

Issues:– Synchronous versus asynchronous.– Reliable versus unreliable.

Winter 2002 21

Distributed Shared Memory

Sharing data among computers that don’t share physical memory.

DSM provides shared memory abstraction.– Read- and write-like primitives.

Needs message passing to convey updates among physically disjoint processing elements.

Winter 2002 22

Deadlocks

Shared data/resource may lead to deadlock: processes get “stuck”.

Example: v is using r1 and requests r2; w is using r2 and requests r1.

v w

Winter 2002 23

Memory Management

Share memory among several processes. Monoprogramming: memory sharing between

OS and program (embedded OSs). Multiprogramming: multiple processes

(partially or totally) in memory.– Swapping.– Virtual memory: paging.

Winter 2002 24

I/O

OS I/O subsystem manages I/O devices.– Device-dependent (device drivers) or independent.

File system:– File as an abstraction.– Basic operations: create, delete, read, write.

Hierarchical file systems.– Dynamically attach tree branches (e.g., mount

system call in UNIX). Access control: permissions.

Winter 2002 25

System Calls Interface between OS and user program: set of

system calls.– E.g., access a file, create a process, etc.

Like making a special procedure call.– System calls executed by kernel.– Calling program pushes parameters onto stack; calls

library; library routine (same name as system call) executes TRAP, switching to kernel mode; OS handles call; returns control to library; library returns to user program.

Example system calls for file system– open, close, read, write, mkdir, rmdir.

Winter 2002 26

System Calls

User-level process

Kernel

Physical machine

System callto access physical resources

System call: implemented by hardware interrupt (trap) which puts processor in supervisor mode and kernel addressspace; executes kernel-supplied handler routine (device driver)executing with interrupts disabled.

Winter 2002 27

Kernels

Executes in supervisor mode.– Privilege to access machine’s physical

resources. User-level process: executes in “user”

mode.– Restricted access to resources.– Address space boundary restrictions.

Winter 2002 28

Kernel Functions Memory management.

– Address space allocation.– Memory protection.

Process management.– Process creation, deletion.– Scheduling.

Resource management.– Device drivers/handlers.

Winter 2002 29

Kernel and Distributed Systems

Inter-process communication: RPC, MP, DSM.

Distributed (Networked) File systems. Some parts may run as user-level and

some as kernel processes.

Winter 2002 30

Be or not to be in the kernel?

Monolithic kernels versus microkernels.

Winter 2002 31

Monolithic kernels

• Examples: Unix, Sprite.

• “Kernel does it all” approach.

• Based on argument that inside kernel, processes execute more efficiently and securely.

• Problems: massive, non-modular, hard to maintain and extend.

Winter 2002 32

Microkernels Take as much out of the kernel as possible. Minimalist approach. Modular and small.

– 10KBytes -> several hundred Kbytes.– Easier to port, maintain and extend.– No fixed definition of what should be in the kernel.– Typically process management, memory

management, IPC. Example: Mach (CMU),

Winter 2002 33

Micro- versus Monolithic Kernels

S1 S4 S3

S4

S1 S4S2 S3

Monolithic kernel Microkernel

Services (file, network).

Kernel code and data

Winter 2002 34

Microkernel

Application

OS Services

Microkernel

Hardware

. Services dynamicallyloaded at appropriateservers.

. Some microkernelsrun service processes only @ user space; others allow them to beloaded into eitherkernel or user space.

Winter 2002 35

Extensible Kernels “Extensible” OS. Provides core set of extensible services +

extension infrastructure. Extensions: allow applications to specialize

the underlying OS to achieve performance and functionality.– Extensions can be loaded into kernel any time.

Example: general purpose OS doesn’t provide adequate disk management for database applications.

Winter 2002 36

Extensions Applications can extend OS servers to

provide better match for its needs. Goal: build general purpose OS that

provides extensibility+safety+performance.

Example: UofWashington’s SPIN kernel.