CS 412 Intro

UMUC CS 412, Sp 97, Introduction

Silberschat and Gavin chapters 1, 2, and 3

Tanenbaum, chapter 1

Introduction - What is an operating system? (S, chapter 1)

First: what is a computer:

Hardware
An operating system
Applications
Users

An operating systems acts something like:

A government
An environment
A resource allocator
A controller

Survey of hardware components:

CPU - central processing unit
Memory
Devices

Monitor
Keyboard
Mouse
CD - compact disk
Tape
Disk drive
Modem
Printer
Network
Sensors
Servos, actuators

No universally accepted definition - perhaps just what a supplier ships

Issues: user convenience and efficiency

Evolution, mostly driven by hardware utilization and CPU vs peripheral speed:

Hardware - bare, program through switches
Assemblers, loaders, linkers
Libraries for reusability
I/O difficulties leads to device driver libraries

buffers
flags
registers
control bits
state bits

Compilers; steps:

load and run compiler, accept high level code, produce assembler code
load and run assembler, input is assembler code, output is machine object code
load and run object code

Batch systems, manual
Automatic job sequencing using a resident monitor

loader, job sequence, control cards, control card interpreters
job deck, see S f 1.3, pg 10
cards to mag tape to CPU to mag tape to cards, sequential access
spool (simultaneous peripheral operation on-line), random access

Jobs

job pool
scheduling and sharing resources
multiprogram, many jobs in memory at same time

Time sharing

many users with real-time access to computer system
interactive
file systems
response time issue
based on processes
virtual memory

Personal computers - their own evolutionary trajectory
Parallel systems

tight and loose coupling
graceful degradation

Distributed systems

speed, reliability, access to resources, cost

Real-time systems

device control

Computer System Structure (S, chapter 2)

Bus-based systems, see S f 2.1, pg 30; plus MMU (memory management unit) and PROM or ROM (programmable read-only memory).

Boot strap program - loaded by ROM, loads OS

OS then waits for events (interrupts)

disable/enable interrupts
traps = S/W interrupts
hardware interrupts
polling

Input/output structure

data goes from and to devices through buffers
Output

prepare buffer
load registers
loop, poll, wait in interrupt, return to user, or return to system

Device status table in OS
Input - on interrupt:

determine interrupt source
look at device status table
route message to requesting process
buffering and type ahead

DMA - direct memory access

card access to memory vs direct byte by byte CPU transfer

Storage

Registers
Cache memory, fast and expensive
Main memory: RAM (random access memory), core, drum; volatile
Secondary storage

RAM Disk
Magnetic disk (track, cylinder, head, sector)
Optical disk
Tape
Paper tape and punch cards

Cache management - copy leads to coherency and consistency problems

Hardware protection

User and monitor (kernel, supervisor, privileged) modes
Privileged instructions
No direct user access to devices
Memory protection (S, chapters 8 & 9)

Base/limit registers and MMU (memory management unit)

CPU protection

CPU hog
Timer with interrupt
Time slice
Context switch
Time limits

Talking to OS - monitor mode from user mode

traps
syscalls
data: trap number, registers, stack, memory with pointers, parameter blocks

Operating System Structures (S, Chapter 3)

Components
Services
System calls
System programs
System structures
Virtual machines
Design and implementation
System generation and configuration

Components or functions. Manage: processes, RAM, secondary storage, I/O, files, security, networking and communications, command interpreter (window and line oriented control), IPC (interprocess communications)

Processes (Who's got the program counter?)

create and delete user and system processes
suspend and resume processes
process synchronization
process communication
deadlock handling
IPC

RAM (memory)

in use map
which processes get ram
allocate and deallocate

Secondary storage

Free space
Storage allocation
Scheduling

Input/output

hide wierdness
buffer cache
general I/O interface
specific hardware drivers

Files

create and delete files
create and delete directories
file and directory manipulation
map files to secondary storage
backups

Security

authorize users
authorize processes
protect resources

Networking

OSI (open systems interconnect) 7-layer stack
TCP/IP (transmission control protocol/internetwork protocol)
process to process

Command interpreter

command line
job control
windows

OS services

Program execution
I/O operations
File system
Communications
Error detection and recovery
Resource allocation
Accounting
Security

System calls

Process control (S chapters 4 and 6)
File system services (S chapters 10 and 11)
Device control
Information (S section 4.1.3)
Communications (S chapter 6)

System programs

File manipulation
Status information
File modification
Programming support
Program loading and execution
Communications
Applications

System Structure

O/S's are large programs or projects
Layered systems
Both user and kernel software elements
Replace parts
Extensions and DLL's

Virtual machines

system development
system compatibility
simulation

Design and implementation

User goals: convenient, easy to learn, easy to use, reliable, safe, fast
System goals: easy to design, implement and maintain, flexible, reliable, error free, efficient

Mechanisms versus policies: what vs how

Implementation: originally in assembly language, nowadays much is in a high level language

System generation

Parameters

CPU
Memory
Devices
Options

Use:

parameter tables, configuration files
substitute elements, programs
compile a new kernel