Comfort and Services

1
Comfort and Services

• How would you feel if your computer had-
• no mouse
• no colour (mono display)
• no floppy disc drive
• no sound output
• no user storage
• no CD-ROM drive
• no Internet connection?

• How would you feel if you stayed in a house
  with-
• no hot water
• no electricity
• no TV
• no kettle
• no phone
• no beds?

2
What is a house?
People(service users)

• The house is a dwelling place which enables
  people to use various facilities in comfort
• A house gives consistent services and interfaces,
  e.g. switches, taps, sockets, aerial leads,
  doors, windows...

House
Hardware (e.g. power stations, satellites, water
mains)
3
What is an OS?
Application Software

• The OS is a software system which sits between
  the hardware and the application software
• An OS give consistent services and interfaces,
  e.g. disc access, keyboard input, video output,
  memory management...

Operating System
Hardware
4
What is an OS?

• The software which gives a computer its
  personality
• Operating systems are programs which improve the
  efficiency and productivity of computer systems.
• Operating systems act as interfaces between user
  programs (application software) and hardware.
• Operating systems turn dumb hardware into
  functioning computers

5
What do operating systems do?

• They interface user commands and inputs
• They control resources (memory, ALU, I/O, etc.)
• they control the running of programs (note
  programs which are running are called processes )
• They make the computer more user friendly
• They handle security.

6
Computing without an OS

• It is possible to ignore the OS and take over the
  hardware directly
• But application software that does this is
• reinventing the wheel
• making life difficult for itself
• probably implementing its own internal OS anyway
• usually a game system which does not need a
  complex, full-featured OS to work
• Modern PC software uses the OS

7
Variety - Different Strokes

• Many PCs use the Windows OS
• Some PCs use UNIX, e.g. Linux, FreeBSD
• Most Macs use MacOS (also AIX, Linux)
• Hand-held computers use Windows mobile CE, Palm,
  Epoc32, GEOS, JavaOS and others
• Minicomputers use VMS, OS/400 and others
• Mainframes often use obscure proprietary systems

8
Operating System Evolution

• The first computers had small quantities of
  memory, limited processing abilities and a highly
  restrictive interface (the keyboard or worse and
  monochrome VDUs or worse!)
• To control the hardware so as perform useful
  tasks, simple instructions had to be given.
• These instruction took the form of typed
  sequences of commands.
• This was the birth of the command-line interface.
• An early but powerful version was UNIX.

9
Operating System Evolution - GUIs

• Most people are used to using a GUI (Graphical
  User Interface) to control a computer.
• The GUI was invented in the early 1970s at Xerox
  PARC (Palo Alto Research Center).
• All modern GUIs are derived from this first GUI.
• The WIMP (Windows, Icons, Menus and Pointers)
  desktop metaphor and mouse also originated during
  the same research.
• Why is Xerox not better known for inventing the
  interface to the modern PC? Why is Microsoft?

10
Operating System Design

• The design of the operating system is very
  closely tied to the hardware platform that it is
  to be run on.
• Especially important are the restrictions placed
  upon it by
• CPU bits per instruction, multi-tasking
  abilities
• System Memory 32 bits 4GB, 16 bits 32MB
• Graphics Card number of bits per pixel colour
  depth.

11
Internet Devices Others

• Wherever there is a CPU there is likely to be an
  OS of some type
• Smart cards, engine management systems, cell
  phones, Internet devices all run some kind of OS
• The real-time OS for embedded systems is an
  area of much development at the moment
• Example the Sega Dreamcast games console runs
  Windows CE OS