Beginning Snapshots

1
Beginning Snapshots

• Chapter 0

2
Objectives

• Give an overview of computer science
• Show its breadth
• Provide context for computer science concepts
• Events from the past
• Describe basic components, organization of a
  computer

3
Areas of Computer Science

• Algorithms and Data Structures
• Architecture
• Artificial Intelligence and Robotics
• Database and Information Retrieval
• Human-Computer Communication

• Numerical and Symbolic Computation
• Operating Systems
• Programming Languages
• Software Methodology and Engineering
• Social and Professional Context

4
Important Concepts in Computer History

• The mechanism of arithmetic
• The stored program
• The graphical user interface
• The computer network

5
Computing Systems

• Computers have two kinds of components
• Hardware physical devices such as
• CPU
• memory
• storage devices
• Software programs such as
• Operating system
• applications
• utilities

6
Hardware CPU

• Central Processing Unit (CPU)
• the brain of the machine
• Circuitry that performs arithmetic and logical ML
  statements
• CPU measurement
• Speed (roughly) in megahertz (millions of
  clock-ticks per second)
• Examples
• Intel Pentium, AMD K6, Motorola PowerPC, Sun
  SPARC,

7
Storage

• Random Access Memory (RAM)
• Main memory, which is fast, but volatile...
• Analogous to a persons short-term memory.
• Many tiny on-off switches
• on is represented by 1, off by 0.
• Each switch is called a binary digit, or bit.
• 8 bits is called a byte.
• 210 bytes 1024 bytes is called a kilobyte (1K)
• 220 bytes is called a megabyte (1M).

8
Storage

• Secondary Memory (Disk)
• Stable storage using magnetic or optical media.
• Analogous to a persons long-term memory.
• Slower to access than RAM.
• Examples
• floppy disk (measured in kilobytes)
• hard disk (measured in gigabytes (230 bytes))
• CD-ROM (measured in megabytes), ...

9
Input and Output

• Input devices
• Instructions and data must be encoded in binary
  form and transmitted to the CPU
• Examples
• keyboard
• mouse, trackball, joystick
• scanner
• audio, video capture boards

10
Input and Output

• Output devices
• Convert data from binary to another form
• Examples
• monitors, printers
• sound, video
• robotics control
• Communication between CPU and peripheral devices
  is through ports
• Ports communicate via the system bus

11
Software OS

• OS acts as the manager of the system,
• Making sure that each hardware device interacts
  smoothly with the others.
• Provides an interface
• Enables user to interact with the computer,
• Awaits user input if no application is running.
• Examples MacOS, Windows-95, Windows-NT, UNIX,
  Linux, Solaris, ...

12
Software Applications

• Applications are non-OS programs
• Perform some useful task
• Including word processors, spreadsheets,
  databases, web browsers, C compilers
• Example C compilers/environments
• CodeWarrior (MacOS, Win95, WinNT, Solaris)
• GNU C (UNIX, Linux)
• Turbo/Borland C (Win95, WinNT)
• Visual C (Win95, WinNT)

13
Software User Programs

• Programs that are neither OS programs nor
  applications are called user programs.
• User programs are what youll be writing in this
  course.

14
What is Programming?

• Computer Program
• A sequence of statements that instruct a computer
  in how to solve a problem.
• Programming
• The act of designing, writing and maintaining a
  program
• Programmers
• People who write programs

15
What kinds of statementsdo computers understand?

• A computer only understands machine
  language statements.
• Characteristics of machine language
• A sequence of ones and zeros
• Cause the computer to perform a particular
  action, such as add, subtract, multiply, ...

16
Machine Language (ML)

• ML statements
• Stored in a computers memory
• Computer memory is a sequence of switches.
• an on switch is represented by 1,
• an off switch is represented by 0.
• ML thus appears to be binary (base-2)
• 0010111010110101

17
Early Computers

• ... required a programmer to write in ML...
• Problem
• Easy to make mistakes!
• Such mistakes are hard to find!
• Not portable -- only runs on one kind of machine!
• Programming was very difficult!

18
A Bright Idea

• Devise a set of abbreviations (mnemonics)
  corresponding to the ML statements
• Create a program (the assembler) to translate
  them into ML.

100111001110010110100110110111
ADD 34, R1MOVE R1,1200CMPR R1, R2
Assembler
19
Advantages and Disadvantages

• Still not portable to different machines
• Each machine had its own set of mnemonics
• Each had its own assembler

• More natural than binary.
• Much easier to read programs
• Much easier to find and fix mistakes

20
High Level Languages

• Improvement on assembly language
• Devise a set of statements that are close to
  human language (if, while, do, ...)
• Create a program to translate them into ML.
• The set of statements is called a high level
  language (HLL)
• The translation program is called a compiler.

21
Contrast Assembler and HLL Compiler

• Assembler translates one mnemonic into one ML
  statement

• Compiler translates one HL statement into several
  ML statements

1010110011110101 0000000000010000 001011101011010
1 0000000000010010 0010111011111101 00000000000101
00
Compiler
z x y
22
Advantage of HLLs

• Programs are easier to read
• Errors are easier to find
• Programs are portable from one computer to
  another
• Assumes the language is standard
• Just create a new compiler which does the
  translation into the correct ML

23
Objectives in Programming A program should solve
a problem

• Correctly
• Efficiently
• Readably
• In user-friendly fashion

• It actually solves the problem
• Without wasting time or space
• Understandable by another person
• In a way that is easy for its user to use

24
Summary of "Levels" of Computer Languages

• Low levelML in binary language
• Medium Level Assembly language
• High Levelas in C

• Hard to read, not portable
• Mnemonics, easier to read, still not portable
• Reads like English and algebra, portable