- Topics discussed in this webnote:
- Logical (functional) view of a computer
- Structure and operation of the RAM memory
- How to store information as numbers in memory
- How to tell what a number mean
- Logical (functional) view of a computer
- This is the most common
view (perception) of a computer
is as follows:
- Component of the computer by their functionality:
- Input devices: allow users to enter input to the computer (mouse, keyboard, microphone, camera)
- Output devices allow the computer to display output to the user (monitor, printer, speaker)
- Input/output devices:
used by the computer to store data and/or communicate with
other computers
(CD-rom, floppy drive, hard drive, modem, network)
- Computer system (that's the box in the middle of the picture)
- Today, the most popular usages
of a computer are:
- Web browsing
- Play games
- Text processing (for homework)
The operations of these tasks differ widely from each other
And yet, they are accomplished using the same machine (a computer) through executing a different computer program
- Computer jargon:
- Hardware =
the physical parts of a computer
- The case containing the computer
- Keyboard
- Terminal
- Mouse
- Etc
- Software =
the computer programs
that you run with a computer
- Web browser
- PC games
- Microsoft Word
- Microsoft Excel
- Etc
We will first study how a computer (hardware) is connected together so it can execute computer programs
Then we will study what computer software does
- Hardware =
the physical parts of a computer
- Logical (functional) view of a
computer
- The input devices,
output devices and
input/output (I/O) devices
are called peripheral devices
- A computer system consists
of:
- The Central Processing Unit
(a.k.a. the CPU)
- The memory or Random Access Memory (RAM)
In this webnote, we will first study the computer (RAM) memory
- The Central Processing Unit
(a.k.a. the CPU)
- Structure of the Memory (RAM)
- The RAM consists of
multiple memory cells:
-
Each memory cell is
uniquely identified by
its memory address
- Memory addresses always starts at
zero (0)
- The last memory address depends
on the amount of memory
installed in the computer system
- Each memory cell can store a small number
- The RAM consists of
multiple memory cells:
- You can compare
the RAM memory with
a large number of
mailboxes:
- Each mailbox is
uniquely identified by
its mailbox number
- Mailbox numbers always starts at
zero (0)
- Each mailbox contains a small slip of paper where you can write down a small number (with pencil so you erase it and write another number later)
- Each mailbox is
uniquely identified by
its mailbox number
- Memory can store and
recall (retrieve)
values for the CPU:
- Each memory cell can
store one number
Example:
In this example:
- Memory location 0 stores the value 13
- Memory location 1 stores the value 3
- Memory location 2 stores the value 0
- Memory location 3 stores the value 45
- ...
- Each memory cell can
store one number
- Each memory cell can
store and recall a value
by the command by the
CPU:
- A memory cell is like
the STO/RCL function
of a calculator:
- Numbers
that are stored in a memory cell
can encode:
- a instruction
- a piece of information
- A memory cell is like
the STO/RCL function
of a calculator:
- Demo:
- Open a terminal
- Execute the command:
- dtcalc
- Click in the text box and enter a number
- Right click in
the Store button and
select a register:
- You can right click the Recall button and select a register to recall the stored value
- Open a terminal
- Computer (RAM) memory:
- The RAM memory works
just like the Store/recall
buttons in the above demo.
- The RAM memory is
under the control of the
CPU:
- The CPU can
store a value in a specific memory location
in the RAM memory
- The CPU can recall the stored value later when it needs it.
- The CPU can
store a value in a specific memory location
in the RAM memory
- The RAM memory works
just like the Store/recall
buttons in the above demo.
- Information can be
stored as numbers
by using an
encoding method
- An encoding method is
simply an agreement on
a representation of some facts
by specific numbers
- 2 common type of things are
represented by numbers inside
a computer:
- The instructions that tells
the computer what to do
- Various kinds of information that are stored and manipulated by the computer.
- The instructions that tells
the computer what to do
- Computer program:
- A computer program (or software) is a (very long) list of instructions that are executed by the computer
Schematically: what a computer program look like
"add x to y" "subtract x from y" "multiply x with y" ....The instructions are not represented in English, but by some number
(Some programs contains over a billion instructions !)
- Another commonly used name for
computer program is
computer application
I will use these 2 terms interchangeably
- Representing computer instructions by numbers:
- A computer can
perform Mathematical operations
and
logical operations:
Example:
- Add
- Subtract
- Multiply
- Divide
- Compare 2 numbers
- And 2 logical value
- Or 2 logical value
- Each operation is represented
by a unique encoding
Example:
- 0 = add
- 1 = subtract
- 2 = multiply
- And so on...
- A computer can
perform Mathematical operations
and
logical operations:
- Computer program: (the naked truth)
- A computer program (or software) is a (very long) list of numbers that represents instructions that are executed by the computer
Schematically: what a computer program look something like
1256 875 7263 ....Each number represents a computer instruction
- A computer is used to
process information
- How is information stored inside a computer ???
- Representing various kinds of information by numbers:
- Same technique is used to encode any type of
information
- Example:
encoding gender information
- 0 = male
- 1 = female
- Example:
encoding marital status information
- 0 = single
- 1 = married
- 2 = divorced
- 3 = widowed
- Same technique is used to encode any type of
information
- In the above examples, we saw that the
number 0 can mean:
- Add (in instruction encoding)
- male (in gender information)
- single (in marital status information)
- We can only tell
what is the meaning of the
number 0 if we
are given:
- context information
- $64,000 question
- Make a correct
English sentence that starts with:
You is .......where you is the subject of the sentence.
- Make a correct
English sentence that starts with:
- Answer:
You is a word in the English language
- Importance of context:
- The word you used in a
sentence such as:
- You are a student
is used in the context of a personal pronoun
- The word you used in a
sentence such as:
- You is a word in the English language
is used in the context of a noun
- The word you used in a
sentence such as:
- If the computer is
executing an instruction,
then:
- The number 0 means "perform an add operation"
- If the computer is
examining gender information,
then:
- The number 0 means "male"
- If the computer is
examining marital status
information,
then:
- The number 0 means "single"