5 basic components of any computer

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5 basic components of any computer and how they
interact
CPU
Output Devices
Main Memory
Input Devices
Secondary Memory
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• CPU (Central Processing Unit)
• Performs program control
• Gets data from main memory (primary storage)
• Operates on at most 2 pieces of data at a time
• Performs calculations
• Arithmetic (, -, , / )
• Logic (lt, lt, gt, gt, !, )
• Boolean result true or false

3

• Memory
• Ordered sequence of storage locations (cells)
• each location has an address
• RAM random access memory (read/write)
• ROM read-only memory
• composed of bits (binary digits a 0 or 1)
• byte 8 bits
• nibble ½ byte 4 bits
• each cell is some number of bytes depending on
• the computer

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1 bit can represent 2 things (0 or 1) gt 21 How
many different things can x bits represent? 22
? 23 ? 24 ? 25 ? 26 ? 27 ? 28
? Kilobyte (K) 1000 bytes (210) Megabyte (M)
1,000,000 bytes (220) Gigabyte (G)
1,000,000,000 bytes (230)
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• Main Memory
• ROM and RAM
• volatile (needs power)
• closest memory to CPU
• limited amount available
• often multi-layers
• Secondary Memory
• RAM
• non-volatile (doesnt need power)
• farther from CPU (longer time to access)
• unlimited storage

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Various Kinds of Input Devices? Various
Kinds of Output Devices?
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• Weve looked at a computers structure,
• now look at software and languages
• -- A computer program is a sequence of steps
  (statements) that are instructions to the
  computer for solving a problem.
• Questions
• What kinds of software are there?
• What language do we use to write programs?
• What kinds of languages are there?
• What language(s) does a computer understand?
• How does all this work??

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Operating Systems (OS)

• An OS is software a computer program
• Provides interface between current program and
  hardware
• Controls peripheral devices such as fetching data
  from memory, sending data to printers, etc.
• Schedules program execution, multitasking
• Sets up memory space for running program
• Protects underlying system from a users program

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Operating Systems contd

• OS is started when computer is turned on it
  boots the computer (from bootstrapping)
• Examples
• Microsoft Windows
• MacOS
• Unix
• Linux

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• Computers understand low-level languages
• machine language is in bits
• for example 11100000 10101010
• might mean place value 10 in cell 20
• assembly language is mnemonic codes
• LOAD R1, 40
• LOAD R2, 20
• ADD R1, R2
• STORE R1, 320X
• Not very convenient for us!

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Humans prefer high-level languages that are
easier for to read and write (more
like English) For example int x // x is a
memory location int y // so is y int
result // and also result x 40 // put
value 40 in x y 20 // put value 20 in y result
x y // put value of x y in result
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What are examples of high-level languages? Java,
??
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Our problem? Computers only understand
low-level language programs need some way
to convert our high-level language programs
to low-level language programs Answer? A
Compiler is software (a program) that takes as
input a high-level language program and converts
it to a functionally equivalent program in a
lower-level language
PHL
PLL
Compiler
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To compile a Java program
Java byte code
Java source code
Java Compiler
Then to execute (run) the program
Java byte code
Java Interpreter
Program output
Java library routines
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• Creating a program
• using TextPad, type in your program code
• need to name the file that stores the program
• file name is the same (exactly) as the program
• class name plus .java
• ex
• public class HelloWorld
• .
• ? file is named HelloWorld.java
• after compiling HelloWorld.java we get
• HelloWorld.class which is executable and
• ready to be run

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/ traditional first program / public class
HelloWorld // every program must have a
"main" method public static void main( String
args ) // Print a
message to the screen
System.out.println("Hello World!!")
// end of main method // end of program
HelloWorld
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• Errors you can make when typing in programs
• missing semicolons ()
• most lines end with a
• mis-spelled words
• Int instead of int
• system.out instead of System.out
• Main instead of main
• be careful! Java is case-sensitive
• unmatched curly braces
• every needs a matching

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Types of Program Errors

• Compile-time errors syntax errors detected
  during the compilation phase results in an
  error message
• Run-time errors cant be detected at
  compile-time, for example
• divide by zero possible here result 20 / x
• Logic errors our thinking or implementation was
  faulty we get an answer but know it isnt
  correct

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Debugging getting rid of bugs

• Compile-time errors
• fix as many errors as you can see start at top
  of error list
• re-compile and start again
• some errors cascade from previous ones and go
  away once others fixed
• Run-time errors often not difficult to fix
• Logic errors hardest to find and fix no
  messages to identify where problem is!