- 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)
What we will learn in CS255 are the things that are inside the the "box" in the middle of the picture
- 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"