What is a Computer? - AndroBenchcsl.skku.edu/uploads/ICE2010S11/1-computer.pdfWhat is a Computer? A computer is … a programmable machine that receives input, stores and manipulates

Jin-Soo Kim ([email protected])Computer Systems Laboratory

Sungkyunkwan Universityhttp://csl.skku.edu

What is a Computer?

What is a Computer?

What is a Computer?

▪ A computer is …

a programmable machine that receives input, stores and manipulates data, and provides output in a useful format.

-- From Wikipedia.org

ICE2010: Introduction to Computer Engineering (Spring 2011) – Jin-Soo Kim ([email protected]) 3

Functions

▪ A function is …a set of input-output pairs such that no two of them have the same first element.

▪ f = {<0,1>, <1,2>, <2,3>, …}or f(0) = 1, f(1) = 2, f(2) = 3, …or f(i) = i + 1 (by formula)


Computers

▪ A computer can be viewed as a “machine” that mysteriously converts input into output.


Image from http://shop.gessato.com

0 f(0) = 1

Example: Sorting


<1, 4, 2, 3> <1, 2, 3, 4>

<2, 1, 3, 4> <1, 2, 3, 4>

Computable Functions

▪ A function f is computable if there is an “algorithm” that computes f.• i.e., there is an algorithm Af such that,

for all input i, Af(i) = f(i)


i f(i)AlgorithmAf

Af(i):input i;add i to 1;output result;

Algorithm

▪ An ordered set of unambiguous steps that produces a result and terminates in a finite time.

Derived from the last name of “Muhammad ibn Musa Al-Khowarizmi”, a Persian mathematician


What is Computer Science?

Misconception I

▪ Computer science is the study of computers.

“Computer science is no more about computers than astronomy is about telescopes, biology is about microscopes, or chemistry is about beakers and test tubes. Science is not about tools. It is about how we use them and what we find out when we do.”

-- Michael R. Fellows and Ian Parberry


Misconception II▪ Computer science is the study of how to

write computer programs.

• Programming is extremely important to study new ideas and build and test new solutions.

• Like the computer itself, it is a tool.

• Computer science is not about programming, but about problem solving.


Misconception III▪ Computer science is the study of the uses

and applications of computers and software.

• Learning to use a software package is no more a part of computer science than driver’s education is a branch of automotive engineering.

• The computer scientist is responsible for specifying, designing, building, and testing software packages as well as the computer systems on which they run.


What is Computer Science?

▪ The study of algorithms, including

1. Their formal and mathematical properties2. Their hardware realizations3. Their linguistic realizations4. Their applications


Complexity▪ Intel Xeon 7560 (8-core): 2.3B transistors


Abstraction

▪ Removes or hides complex details, leaving only the information necessary to accomplish our goal

▪ A key concept to tame the complexity!


Abstraction Everywhere


Levels of Abstraction


Operating System

Architecture

Programming languages & compilers

Data structures & algorithms

Application programs

Microarchitecture

Hardware Description Languages

Digital logic

VLSI layout

Processing, Fabrication

Chemistry, Physics

Computer Science Is

▪ Science• Discover truth by scientific methods

▪ Engineering• Achieve a solution that works for a particular problem• Develop “good enough” heuristics• Performance/cost

▪ Art• Elegance, beauty, and simplicity• Make complex ideas more comprehensible


How To Be A Successful Computer Scientist (1)

▪ A passion for finding elegant solutions

▪ An ability to use mathematical analysis and logical rigor to evaluate such solutions

▪ Creativity in modeling complex problems through the use of abstractions


Source: http://www.cs.bu.edu/AboutCS/WhatIsCS.pdf

How To Be A Successful Computer Scientist (2)

▪ Attention to details and hidden assumptions

▪ An ability to recognize variants of the same problem in different settings

▪ Being able to retarget known efficient solutions to problems in new settings


Source: http://www.cs.bu.edu/AboutCS/WhatIsCS.pdf

History of Computing

Early History (0)▪ Stonehenge

• 2500BC, England• Calendar? Astrological calculator?


Early History (1)

▪ Abacus• 16th century BC• An early device for recording

numeric values and performing basic arithmetic

▪ “Pascaline” or Pascal’s Calculator• 1642 by Blaise Pascal• Mechanical device to add,

subtract, divide & multiply


Early History (2)▪ Jacquard Loom

• 1801 by Joseph Jacquard• Use of punched cards to control

a sequence of operations

▪ Analytical Engine• 1837 by Charles Babbage• A design for a mechanical

general-purpose computer• Too complex to be built


Early History (3)▪ Ada Lovelace (1815-1852)

• Worked on the analytical engine• The first programmer

▪ Alan Turing (1912-1954)• Invented “Turing machine”,

the foundation of computing • Breaking German ciphers in WWII• Turing test• “Turing Award”


Early History (4)▪ ENIAC (1946)

• Electronic Numerical Integrator And Computer• The first general-purpose electronic computer• Programmed by plugboard and switches


1st Gen. (1951-1959): HW▪ Vacuum Tubes

• Large, not very reliable• Generated a lot of heat

▪ Magnetic Drum• Memory device that rotated

under a read/write head

▪ Card Readers Magnetic Tape Drives• Sequential auxiliary storage devices


2nd Gen. (1959-1965): HW▪ Transistor

• Replaced vacuum tube, fast, small, durable, cheap

▪ Magnetic Cores• Replaced magnetic drums,

information available instantly

▪ Magnetic Disks• Replaced magnetic tape,

data can be accessed directly


3rd Gen. (1965-1971): HW

▪ Integrated Circuits (ICs)• Replaced circuit boards, smaller, cheaper,

faster, more reliable

▪ Transistors• Now used for memory construction

▪ Terminal• An input/output device with a keyboard and

screen


4th Gen. (1971-?): HW▪ Large-scale Integration (VLSIs)

• Great advances in chip technology

▪ PCs and Workstations• New companies: Apple, Sun, Dell, …

▪ Laptops• Everyone has his/her own portable computer

▪ Parallel computing▪ Networking (Internet)


1st Gen. (1951-1959): SW

▪ Machine Language• Computer programs written in binary

▪ Assembly Languages and Translators• Programs written using mnemonics, which

were translated into machine language

▪ Application programmers (in Assembly) vs. Systems programmers


2nd Gen. (1959-1965): SW▪ High-level Languages

• Fortran, COBOL, Lisp, …


3rd Gen. (1965-1971): SW▪ Operating systems▪ Programming for general public

• C


4th Gen. (1971-1989): SW

▪ Structured programming• Pascal• C++

▪ New application software for users• Spreadsheets• Word processors• Database Management Systems (DBMSes), …


5th Gen. (1990~Present)▪ Operating systems with GUIs

• Microsoft Windows

▪ Object-oriented design/programming• Based on a hierarchy of data objects • Java

▪ World Wide Web▪ Mobile “apps”▪ New users with no computer knowledge


Documents

What is a Computer? - AndroBenchcsl.skku.edu/uploads/ICE2010S11/1-computer.pdfWhat is a Computer? A computer is … a programmable machine that receives input, stores and manipulates