Physical organization of a computer

What a computer looks like physically:

Physical organization of a computer

Categories of the computer components:

Logical (functional) organization of a computer

What a computer looks like logically (= by their function):

What a computer looks like from inside

When you open the computer case, the inside of the computer looks like this:

What a computer looks like from inside

The computer system consists of only 2 (functional) parts:

What a computer looks like from inside

The RAM (or Random Access Memory) stores/contains computer programs:

What a computer looks like from inside

The CPU (or Central Processing Unit) execute instructions in programs:

Updated logical (functional) organization of a computer

What a computer looks like logically (= by their function):

Components of a computer

A computer consists of 4 types of components:

Central Processing Unit (= CPU) = "brain" of a computer Main memory (= RAM) = storage space of a computer Input devices = devices used to receive data into the computer 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
  A computer can only store numbers !!!

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

Question: how can a computer store things (like text) other than numbers ??

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.

How can a computer tell the meaning of a number ?

The computer program can tell the difference because:

- When the program is processing marital status information, the code used will be:
       0 = single      2 = divorsed
       1 = married     3 = widowed
- When the computer is executing an instruction in the program, the code used will be:
       0 = add         2 = multiply     ,,,
       1 = subtract    3 = divide       ...
That's how the computer can tell what does 0 mean (`single` or `add`)

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