Physical organization of a computer

  • What a computer looks like physically:

Logical (functional) organization of a computer

  • What a computer looks like logically (= functionally):

Components of a computer

A computer consists of 4 types of components:

  1. Central Processing Unit (= CPU) = "brain" of a computer
  2. Main memory (= RAM) = storage space of a computer

  3. Input devices = devices used to receive data into the computer
  4. Output devices = devices used to output data from the computer

We take a closer look at the computer (main) memory component next

Computer memory (a.k.a.: Random Access Memory or RAM)

  • The main memory or RAM consists of many memory cells:

  • Each memory cell is uniquely identified by a memory address (which is an integer number)

      • Note: memory addresses always starts at the number zero (0)

  • Each memory cell can store a small number

Analogy to help you understand a computer memory

  • The main memory or RAM is similar to a collection of mail boxes:

  • Each mail box is uniquely identified by an integer mail box number

      • Imagine that: each mail box contains a (small) slip of paper !!

  • Each memory cell's slip of paper can store a small number

Operations that a computer can perform on the main memory

  • The computer can perform 2 operations on the main memory:

      1. Write operation:   the computer stores a number into one or more memory cells at a specific memory address

      2. Read operation:   the computer retrieves the number from one or more memory cells at a specific memory address

Analogy to help you understand the write and read operations to a computer memory

  • The write operation and the read operation to the computer memory is similar to the store and recall operations of a calculator:

How does the computer store information using just numbers ?

  • Information is stored inside a computer as numbers by using an encoding method

  • An encoding method is an agreement on how to represent certain facts by a code (= specific number)

    Example: encoding the marital status information 

       0 = single      2 = divorsed
 1 = married     3 = widowed

How can a computer tell the meaning of a number ?

Problem description:

  • We just saw how to represent information on a person's marital status: 

       0 = single      2 = divorsed
 1 = married     3 = widowed

  • There are other kinds of information too.

    Example: encoding method for computer instructions 

       0 = add         2 = multiply     ,,,
 1 = subtract    3 = divide       ...

  • Problem:   what does 0 mean ???     (single ? or add ?)

How can a computer tell the meaning of a number ?

Answer to the representation conundrum:

  • The meaning of a code (like the number 0) can only be determined when the context is known/given:

      • When the computer is examining some marital status data, the number 0 means: single

      • When the computer is executing a computer instruction, the number 0 means: the add instruction

  • Analogy to help you understand the concept of context:

      • Make a correct English sentence that begins with: You is ....     

The context of the word You

  • When you use the word You as a personal pronoun (which is the common case), you must use You are ...

    Example: 

        You are a person.

  • You can use the word You as a noun !

    Example: 

        You is an English word.