Chapter 1: Introduction and History
 Where
does the operating system fit in
a computing system?
 What does the operating system
achieve?
 What are the general OS functions?
 Who needs an operating system?
 What is operating system?
 History of operating system
Where does the OS fit in?


The layer between
the hardware and
the user program
(application
programs).
OS is a software
system that directly
interacts with the
hardware.
User programs
Operating system interface
Operating system
Hardware interface
Hardware

Hardware


CPU, registers, disks, monitors, etc
Hardware interface
 the instruction set


Operating system


Implements the OS interface + resource management
OS interface


other things like interrupt – anything that a programmer
needs to know in order to write programs that use the
hardware.
The enhanced instruction set: hardware instruction set +
special instructions called “traps” or “system calls”.
User programs:

Instructions in the enhanced instruction set + data

Question: How many of you have dealt with
the OS (enhanced) interface before?

One more layer between a typical user program
and the OS interface, the programming
environment (compiler + run time library).

cout << “hello world.\n”  write(1, “hello world.\n”, 13);
User programs
programming environment
Operating system interface
Operating system
Hardware interface
Hardware
What does the OS achieve?

Make it easy to write programs

Add more powerful instructions to the hardware
instruction set.

What kind of instructions are added?


Common functions used by many different applications.
E.g. write (fileno, buf, len);
 Resource

virtualization
E.g. the illusion of Infinite memory.
What does the OS achieve?

Make it easy to run programs

How does a program run on the raw machine?


The program is in memory, starting from program
counter (pc), run one instruction, goto the next
instruction, run until the halt instruction.
How do you run a program?

g++ helloworld.cpp and then a.out.
 The
OS must fill the gap between how
you run a program and how the
hardware runs a program. The OS must
be able to:







Take the user command (g++, a.out, etc) – shell
Find the executable file (g++ or a.out) – File system
Load the executable into memory – memory management
Set the registers properly (e.g. pc = starting address of the
executable)
When there are multiple programs running, the OS must
make each program feel like it solely owns the whole
machine (CPU, memory, registers) – virtual machine for
each process
Manage processes.
OS functionality: Implements the OS interface
+ resource management
What does an OS achieve?
 It
hides the complexity and limitations of
hardware (hardware interface) and
creates a simpler, more powerful
abstraction (OS interface).
Hardware reality vs. OS
abstraction
Reality
Abstraction
A single CPU
Multiple CPUs
Limited RAM capacity
Infinite capacity
Mechanical disk
Memory speed access
Insecure and
unreliable networks
Many physical
machines
Reliable and secure
A single machine
What are the general OS
functions?
 Standard
 Screen
services
display, disk accesses, etc
 Coordination
 Protection,
fairness
among applications
correctness, efficiency, and
Coordination

Example: Protection

Applications should not crash one another



Address space: all memory addresses that an
application can touch.
Address space for one process is separated from
address space for another process and from the OS.
Applications should not crash the OS

Dual-mode operations



Kernel mode: some instructions can only be executed by
the OS (must be executed with a kernel mode).
User mode: an application can only access its own
address space
Examples of kernel mode instructions?
What is the operating system?

OS is the software layer between the
hardware and user programs.
 OS is the ultimate API.
 OS is the first program that runs when the
computer boots up.
 OS is the program that is always running.
 OS is the resource manager.
 OS is the creator of the virtual machine.
Resources managed by OS
 CPU:
process management
 Memory: memory management
 Storage: storage and file management
 I/O devices: I/O management
Who needs OS?
 OS
makes a computer easier to use
 All
general purpose computers need OS.
A
better question: Who does not need
OS?
 Some
very specialized systems that
usually do one thing (OS can be
embedded in the application).
Microwave oven control
 MP3 players, etc.

History of OS: Change!
1980
Speed
2000
Factor
CPU
1 MIPS
1,000 MIPS
1,000
Memory
500 ns
2 ns
250
Disk
18 ms
2 ms
9
Modem
300 bits/sec
56 Kbits/sec
200
Memory
64 Kbytes
128 Mbytes
2,000
Disk
1 Mbytes
6 Gbytes
6,000
Cost
Per MIP
$100K
<= $1
100,000
Other
Address bits
8
64
8
Users/machine
10s
<=1
.01
Capacity
History Phase I: Hardware
Expensive, Humans Cheap
 Hardware:
mainframes
 OS: human operators
 Handle
one job (a unit of processing) at a
time
 Computer time
wasted while
operators walk
around the
machine room
OS Design Goal
 Efficient
use of the hardware
 Batch
system: collects a batch of jobs
before processing them and printing out
results

Job collection, job processing, and printing out
results can occur concurrently
 Multiprogramming:
multiple programs
can run concurrently

Example: I/O-bound jobs and CPU-bound jobs
History Phase II: Hardware
Cheap, Humans Expensive
 Hardware:
terminals
 OS design goal: more efficient use of
human resources
 Timesharing
systems: each user can
afford to own
terminals to interact
with machines
History Phase III: Hardware Very
Cheap, Humans Very Expensive
 Hardware:
personal computers
 OS design goal: allowing a user to
perform many tasks at the same time
 Multitasking:
the ability to run multiple
programs on the same machine at the
same time
 Multiprocessing: the ability
to use multiple processors
on the same machine
History Phase IV: Distributed
Systems
 Hardware:
computers with networks
 OS design goal: ease of resource
sharing among machines
The Bottom Line
OS designs need to adapt to changing
technology