Introduction to Computer
Science
Ariel Shamir,
Inter Disciplinary Center
Herzliya Israel, Fall 2007
10 October 2007
© Ariel Shamir
1
Course Overview
•
Introduce basic terms and concepts
•Introduce
of computer science
•
Acquire basic programming skills
•Acquire
•
Understand general principles in CS
•Understand
•
Learn a modern object oriented
•Learn
programming language
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Course Methodology
Lectures
Reading & books
Recitations
Programming exercises & tutors
The course site & the web
Support Structures FOR YOU!
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The Course Web Site
Administration & regulation
Information & downloads
Exercises (receive & submit)
Newsgroup!!!
Go to:
www1.idc.ac.il/coursesftp/cs/intro1/
www1.idc.ac.il/coursesftp/cs/intro1/
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Information Source
Possible course books:
•• ““Java:
Java: and
”, W.
Programming
Savitch
and introduction
introduction to
to CS
CS &
& Programming”
Programming”,
W. Savitch.
Savitch..
•• "Java
”,
Design
"Java Software
Software Solutions
Solutions -- Foundations
Foundations of
of Program
Program Design”
Design”,
John
John Lewis
Lewis &
& William
William Loftus.
Loftus.
•• "The
“, Mary
Tutorial
Campione
Walrath
"The Java
Java Tutorial“
Tutorial“,
Mary Campione,
Campione,, Kathy
Kathy Walrath.
Walrath..
•• "The
“, Ken
Language
"The Java
Java Programming
Programming Language“
Language“,
Ken Arnold,
Arnold, James
James
Gosling.
Gosling.
•• More
…(check the
books
More books…
books…(check
the site!):
site!):
Go to
www1.idc.ac.il/coursesftp/cs/intro1/
www1.idc.ac.il/coursesftp/cs/intro1/
Literature.htm
Literature.htm
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Lecture Overview
1. What is a computer?
2. How is a typical computer built
3. Algorithms
4. Programming
5. Introducing Java
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3
Why Use Computers?
Computers are very good at:
•
• processing
processing data
data in
in aa short
short time,
time,
•
• storing
storing and
and retrieving
retrieving large
large bulks
bulks of
of data,
data,
•
• transferring
transferring large
large bulks
bulks of
of data
data across
across sites
sites
Things that people are bad at, or need help
at or simply hate to do.
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What Is a Computer?
Computers
Computers are
are
computational
computational machines
machines that
that
can
…
tasks
can carry
carry out
out given
given tasks…
tasks…
(???)
(???)
Computational
Computational machines:
machines:
hardware
hardware
Given
Given tasks:
tasks: software
software
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4
“Computational
Machine”
Storage
Computation
Network
Do it faster, and do it with larger amounts
of data. The main parameters are therefore
Time and space!
space!
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Time & Space!
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The Machine (Hardware)
Storage
Memory Disks
Computation
CPU
Network
I/O
Network
Other peripherals: Video, Audio…
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John Von Neumann
1945:
1945: John
John von
von
Neumann
Neumann wrote
wrote "First
"First
Draft
Draft of
of aa Report
Report on
on
the
the EDVAC"
EDVAC" in
in which
which
he
he outlined
outlined the
the
architecture
architecture of
of aa
stored-program
stored
stored-program
computer.
computer.
http://inventors.about.com/library/blcoindex.htm
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Where We Were
The
The ENIAC
ENIAC contained
contained 17,468
17,468 vacuum
vacuum tubes,
tubes, along
along
with
with 70,000
70,000 resistors,
resistors, 10,000
10,000 capacitors,
capacitors, 1,500
1,500
relays,
relays, 6,000
6,000 manual
manual switches
switches and
and 55 million
million
soldered
soldered joints.
joints. It
It covered
covered 1800
1800 square
square feet
feet (167
(167
square
square meters)
meters) of
of floor
floor space,
space, weighed
weighed 30
30 tons,
tons,
consumed
consumed 160
160 kilowatts
kilowatts of
of electrical
electrical power.
power. In
In
one
one second,
second, the
the ENIAC
ENIAC could
could perform
perform 5,000
5,000
additions,
additions, 357
357 multiplications
multiplications or
or 38
38 divisions.
divisions.
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Today…
Blue Gene (LLNL) is the
world's fastest computer, at
360 TFLOPS (1000000000000
12 FLOPS):
= 1012
Cluster of nodes where up to
1024 Compute nodes plus
additional IO nodes in a
standard 19" cabinet
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Von - Newman
Architecture
Long term storage
I/O devices
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Opening the Hood of
Your PC
Peripherials
Monitor
CPU
Chip
Motherboard
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Memory Chips
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Computer Architecture
•
The CPU and main memory are the two
•The
key hardware components
•
All other devices are considered
•All
peripherals. Controllers coordinate the
activities of specific peripherals
•
Binary information moves between
•Binary
devices across a group of wires called a
bus
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The Bus
Main
memory
CPU
Bus
Video
controller
Monitor
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Disk
controller
Hard
disk
Floppy
disk
© Ariel Shamir
Controller
other
peripherals
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9
Memory Hierarchy
The computer memory divided into:
•• Main
Main memory.
memory.
•• Secondary
).
tapes
Secondary memory
memory (disks,
(disks, flash,
flash, tapes).
tapes).
Main memory is volatile - stored
information is lost if the electric power is
removed, but it is FAST!
Secondary memory devices are
nonvolatile, but generally much slower.
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Storage Capacity Units
Every memory device has a storage
capacity, indicating the number of bytes it
can hold.
Capacity unit
Symbol
Actual size
kilobyte
KB
210 = 1024
megabyte
MB
220 = 1048576
gigabyte
GB
230 (over 1 billion)
terabyte
TB
240 (over 1 trillion)
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Main Memory
••The
The main
main memory
memory is
is divided
divided into
into memory
memory
locations
locations called
called cells.
cells.
••Each
Each memory
memory location
location has
has an
an address
address which
which
uniquely
uniquely identifies
identifies it.
it.
••Data
Data stored
stored in
in the
the main
main memory
memory can
can be
be stored
stored
in
in one
one or
or more
more consecutive
consecutive memory
memory locations.
locations.
•• It
It is
is termed
termed RAM
RAM –– Random
Random Access,
Access, as
as access
access
to
to any
any random
random address
address takes
takes (approximately)
(approximately) the
the
same
…)
tapes
same (compare
(compare for
for instance
instance to
to tapes…
tapes…)
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Main Memory Cells
3456
3457
01101010
Memory location - cell
(usually holds 8 bits,
or 1 byte)
3458
3459
3500
3501
Each memory cell has a
unique numeric address
which identifies it
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Main Memory Cells
3456
3457
3458
3459
01101010
3500
10110001
3501
The address of such values will
be the address of the first byte
of the cells holding the value
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Values larger than
8 bits are stored in
consecutive cells
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The Central Processing
Unit
•
A central processing unit (CPU) is
•A
also called a microprocessor
•
The CPU is a single "chip" on the
•The
order of one square inch in size
•
It is the brain of the computer
•It
•
The job of the CPU is to execute
•The
programs: it continuously follows
the fetch-decodefetch
decode-execute cycle
fetch-decode-execute
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Inside the CPU
Arithmetic / Logic Unit
Coordinates
processing steps
Control Unit
Small memory units
capable of storing
information
Registers
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Performs calculations
and decisions
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Machine Execution?
How does a piece of physical
hardware machine carry out
instructions?
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Executing a Program
•
Programs are represented digitally in
•Programs
machine language as a list of numbers.
•
Each number represents either the code of
•Each
an instruction or some data.
•
The program is loaded from disk.
•The
•
The CPU fetches the instructions from
•The
memory one after another and executes
them (execution cycle).
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Machine Language
Each computer has a limited set of
machine language instructions
The instructions are very elementary
•• Add
Add two
two integers
integers
•• Test
Test if
if aa given
given integer
integer is
is zero
zero
The strength of computers is due to their
capability of executing millions of simple
instructions per second
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Machine Code
Instructions
The machine code is a sequence of numbers
representing
•• Instruction
Instruction codes
codes
•• Data
Data values
values
…… 0011
0011 92FD
92FD 0007
0007 0014
0014 ……
…… LOAD
LOAD 92FD
92FD ADD
ADD
20
20 ……
““Load
Load whatever is in address 92FD in
memory and add 20 to it”
it”
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Program Loading &
Fetching
01001011
10111001
01010011
11001100
Load
01001011
10111001
01010011
11001100
Fetch
01110
CPU
Disk
Memory
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Fetch-decode-execute
Cycle
Retrieve an instruction from main
memory
fetch
execute
decode
Determine what the
instruction is
Carry out the
instruction
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Execution Cycle
Fetch D3
…5F 88 D3 04 01 F7…
Decode D3 = ADD
Execute
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Execution Cycle
…5F 88 D3 04 01 F7…
Fetch D3
Decode D3 = ADD
Execute 4
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Execution Cycle
Fetch D3
…5F 88 D3 04 01 F7…
Decode D3 = ADD
Execute 4+1
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Execution Cycle
Fetch D3
…5F 88 D3 04 01 F7…
Decode D3 = ADD
Execute 4+1=5
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Execution Cycle Cont.
Fetch F7
…5F 88 D3 04 01 F7…
Decode
Execute
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CPU Control
•
The speed of a CPU (i.e. the fetch-decodefetch
decode•The
fetch-decodeexecute cycle) is controlled by the system
clock
•
The system clock generates an electronic
•The
pulse at regular intervals which
coordinate the activities of the CPU
•
The speed is measured in megahertz
•The
((MHz)
MHz) or Gigahertz (GHz)
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CPU & Memory
Connection
The main memory stores not only
data but also the programs!
The CPU continuously retrieves
information from the memory in the
execution cycle!
The CPU – memory connection is the
bottleneck of computation!
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“Given Tasks” - Software
Computers do only what we tell them
to – they are deterministic machines!
Inputs
What is a task?
A process that gets inputs
related to the task, and outputs
data which represent the result
of executing the task.
Process
Outputs
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Task Examples
Computing
Computing taxes
taxes for
for employees
employees of
of aa company
company
•• Inputs:
Inputs: textual
textual and
and numerical
numerical data
data representing
representing information
information
about
about the
the employees
employees
•• Output:
Output: formatted
formatted textual
textual tax
tax reports
reports
F15
F15 flight
flight simulator
simulator
•• Inputs:
Inputs: joystick
joystick signals
signals and
and key
key strokes
strokes from
from the
the user
user
•• Output:
’s view
pilot
Output: image
image data
data representing
representing the
the pilot’
pilot’s
view
Search
Search engine
engine
•• Input:
Input: keywords
keywords
•• Output:
Output: locations
locations in
in internet
internet where
where keywords
keywords found
found
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Algorithms – the “How”
An algorithm is a
procedure for
executing a given
task.
Inputs
An algorithm
consist of a list of
instructions.
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Algorithm
Outputs
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Al-Khowarizmi
Born in Uzbekistan (780AD).
Worked as a mathematician in
Baghdad (considered as founder of
modern algebra).
He believed that any math
problem, no matter how difficult it
may be, could be solved if broken
into smaller steps and logically
derive the correct answer!
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Real Life Example
An algorithm for fixing a flat tier:
Take
Take out
out the
the screws
screws of
of the
the tier
tier
Lift
Lift the
the car
car on
on aa jack
jack
Flat tier car
Remove
Remove the
the flat
flat tier
tier
Mount
Mount the
the reserve
reserve wheel
wheel
Algorithm
Tighten
Tighten back
back the
the screws
screws
Lower
Lower back
back the
the car
car
Drivable car
Fasten
Fasten the
the screws
screws
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Mathematical Algorithm
Algorithm:
Algorithm:
For
For all
all integers
integers ii such
such
that
that 1<i<n
1<i<n
A number n
IfIf ii divides
divides nn
Output
Output false
false
Algorithm
Output
Output true
true
What does this
algorithms do?
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True or False
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Measuring Algorithms:
Complexity
•
The efficiency of the algorithm is
•The
often called it’
’s complexity
it
it’s
•
In general terms:
•In
Complexity
Complexity =
= cost
cost in
in time
time and
and space
space
•
Usually computed as a function of
•Usually
the size of the input
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Example: Searching
Find a phone number in a 1000 number
phone book.
•• Linear
Linear search:
search: could
could take
take 1000
1000 checks!
checks!
•• Binary
Binary search:
search:
1000,500,250,125,63,32,16,8,4,2,1,
1000,500,250,125,63,32,16,8,4,2,1,
mostly
mostly 10
10 steps!
steps!
How many jumps in the general case?
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Algorithms in CS
•
• Is
Is there
there an
an algorithm
algorithm for
for every
every task?
task?
•
• How
How can
can we
we know
know if
if an
an algorithm
algorithm is
is
correct?
correct?
•
• What
What is
is the
the time/space
time/space complexity?
complexity?
•
• What
What is
is the
the best
best algorithm
algorithm for
for aa given
given task?
task?
•
• What
What is
is the
the best
best way
way to
to express
express an
an
algorithm?
algorithm?
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From Algorithm to
Execution Cycle
Algorithm/Model
Execution Cycle
Hardware
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Computer Programs
•
An algorithm is described to the
•An
computer as a computer program.
program.
•
A computer program is simply a list
•A
of unambiguous instructions meant
to be followed by a computer.
•
The operations sequence has to be
•The
correct or the program will fail.
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Program Compilation
•
A program written in any high level
•A
computer language (java, C++, basic)
must be translated into the machine
language in order to be executed.
•
The translation process is called
•The
Compilation (or Assembly)
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Summary
Algorithm/Model
Java
Compilation
Next few
lectures
Machine Code
Execution Cycle
Hardware
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