An Introduction to
Computers
August 12, 2008
Mrs. C. Furman
4 Tasks of a Computer
• Input Data – keyboard, mouse, scanner,
microphone, digital camera, CD-RW/DVD
drive, and disk drive.
• Store Data – integrated circuits.
• Process Data – CPU, where decisions are
made.
• Output Data – monitors, printers, CDRW’s, disk drives and memory keys store
data and speakers.
CPU
• Arithmetic Logic Unit, which can perform
arithmetic and logic operations
• Executes instructions fast.
• Speed is determined by the computer’s
clock rate.
• Clock Rate - measured in megahertz
(MHz, million cycles per second) and
gigahertz (GHz, billion cycles per second)
Memory
• ROM: Read Only Memory – most basic
operations
• RAM: Random Access Memory – primary
storage or main memory – data and
instructions are temporarily stored
• RAM can be written to secondary
storage.
• Secondary Storage – floppy disk, hard
disk, memory key, or CD- RW.
Programs
• Application Software
– Word, powerpoint, games…
• Operating System Software – OS – run
automatically when the computer is turned
on and is used to control processing and
peripherals, run application software and
control input and output.
– Windows, Mac OS X Tiger, Unix, and Linux
Programming Languages
• A set of words, codes and symbols that
allow a programmer to give instructions to
the computer.
• Low – level and High – level programs…
Low – Level Languages
• Machine language
– first generation language.
– Consists of 0’s and 1’s
• Assembly language
– Same instructions and structures as machine
language
– Uses meaningful names or abbreviations
instead of numbers.
– Second generation language.
High-Level Languages
•
•
•
•
•
•
Third generation languages
Developed in late 1950s
English-like instructions
Easier to use than machine language
Fortran, Pascal, C, C++, Java
Compilers – program that convert high-level
language into machine language.
• Interpreter – also translates the program but
does it line by line, executing as they go.
How is Data Stored?
Data – computer representation of
something in the real world.
Circuits – 2 states ON /OFF
Imagine 2 light bulbs / 2 switches, what are
the possible combinations?
OFF / OFF
OFF / ON
ON / OFF
ON / ON
What about 3 lights? How
many combinations?
What about 8 lights?
Apply to the computer…
• Use a special number system: Binary
number system.
• Decimal Number System: base 10 , digits
0 – 9. (Our number system)
• Binary Number System: base 2, digits 0
and 1. 0 represents off (false), 1
represents on (true).
• A single binary digit is called a bit.
Converting Binary to Decimal
Decimal Numbers:
7403 = 7 x1000 + 4x100+ 0x10 + 3 x 1
3x100 = 3
0x101 = 0
4x102 = 400
7x103 = 7000
7403
Binary to Decimal
Same process as previous slide, but base 2
8 bits in 1 byte:
1011 0110
0x20 = 0
1x21 = 2
Total: 182
2
1x2 = 4
0x23 = 0
1x24 = 16
1x25 = 32
0x26 = 0
1x27 = 128
8 bits = 1 byte
What’s the number of combinations in 1
byte?
What numbers can be represented with 1
byte?
Examples
a. 1111 0000
b. 1010 1010
c. 1100 1100
d. 0011 0011
Converting Decimal to Binary
Binary Is base 2
We multiply to go from binary to decimal.
We divide to go from decimal to binary.
Right most digit tells even or odd. 1 – even
0 – odd.
Convert Decimal to Binary
a. Convert 210 to binary.
b. 151
Hexadecimal
• Hexadecimal: Used to represent 4 binary
digits.
1111 = 15 and 0000 = 0, so it is base 16.
Digits 0 – 9 plus A – F
A:10, B:11, C:12, D:13, E:14, F:15
Hexadecimal to decimal
1f
15x160 = 15
1x161 = 16
31
Change from Hexadecimal to
Binary and Decimal
0
A
19
1E
What is the decimal equivalent?
1112
2C16