Computer Systems Components
1. Hardware: Tangible Physical devices
2. Software: Intangible pieces of instructions, called
programs written in various languages.
Three Levels of languages:
Machine languages:
Only languages computers understand which are
made up of binary strings/patterns like:
010111001100011.
Very hard for humans.
Assembly languages:
Machine languages in alphanumeric form
like:
MOVE R1, R2
ADD R1, ABC
Needs a translator called Assembler.
A little bit closer to humans and easier than
Machine languages.
High-Level languages:
Java, C++, Pascal, Ada, FORTRAN, COBOL
Very close and familiar to humans.
Very far from computers.
Need translators called Compilers or Interpreters
If (A=B) Print ("Beautiful Day")
Else Print ("Gloomy Day")
a. System software
b. Application software
System Software.
Mostly to manage computer resources for the human users
to use computers easily and efficiently.
Operating Systems.
Languages Translators:
Compilers, Interpreters, Assemblers
Loaders:
Loading (storing) programs into Computer
memory for immediate execution.
CPU Scheduler:
CPU: Central Processing Unit
Brain of the computer.
Executing all instructions and
Processing data.
A scheduler for multi-users and/or multi-tasks.
Memory Manager
Efficient utilization of Main Memory among
Users, Programs, and Processes.
Secondary Storage Manager
Secondary Storage:
Hard Disk (Drive-C)
Floppy diskettes (Drive-A)
CD-ROM(Read-Only) or Recordable CD (Drive-E)
File Manager
File: A Collection of related pieces of
information to be stored in a secondary
storage device.
Each file is identified by a unique file name
that has two parts separated by a "dot"
name and extension (or type)
The Type typically indicates the kind of
information contained in that file.
My.DAT (Data file)
Your.TXT (Text file)
Her.EXE (Executable file, called
Application, ready for
computer execution)
Their.DOC (WORD produced Document)
His.HTML or Her.htm (WWW Page)
Windows Vista (Successor of XP)
GUI (Graphic User Interface) based O.S. for PC.
It enables users to use Menu to select and issue a
command for the computer to execute for us
simply by clicking the Mouse left button.
Mouse has two buttons: Left and Right
Left button
1. Click (Single-click)
for a "Selection" to select an item such
as a command or a computer component.
2. Double Click: Clicking it twice in a row
quickly.
for either opening the selected item
(like a file) or executing (like an
application)
Right button
Usually single-clicked for the
Shortcut Menu of the selected item.
The shortcut menu contains some
commonly used commands depending upon
the selected item including:
Open
Copy
Cut
Explore
Create Shortcut
New
Rename
Delete
Properties.
Application Software
A piece of program dedicated to solving a particular
kind of tasks, not related to direct management of
computer resources,
very small to very large/complex,
like solving a linear equation, calculating payroll,
or analyzing the entire US census.
Many of these are commercially available like
those we will learn in this course.
WORD2007: Word processor that makes a ready-to-read document or paper like this note.
EXCEL2007: SpreadSheet application for business operation
ACCESS2007: Data Base management for
efficient organization, maintenance and retrieval
of large amount of information like a
university semester student registration data.
POWERPOINT2007: Slide presentation
Microsoft Internet Explorer:
WWW Webpage browser such as Internet Explorer and Netscapethat displays HTML documents.
Hardware.
consists of
EU (Execution Unit) generally referred to as CPU(Central Processing Unit)
Main Memory
Secondary Storage devices (such as floppy diskette and CD and Hard-disk)
I/O (input/output) devices (Peripheral devices)
Interfaces between the CPU and human users.
Input devices: For giving the CPU some information
mouse
keyboard
scanner (for image or text inputs)
output devices: For getting information from the CPU
monitor (CRT, Cathode Ray Tube)
not permanent
printer
permanent
1. EU (Execution Unit), commonly known as CPU (Central Processing Unit)
Executes instructions as the brain of computer.
It has three parts:
1.1 CU (Control Unit)
Controls all parts of the computer
by generating and emitting Synchronizing Pulses.
Typically, the speed of these pulses, measured in cycles/second, is used as
the Speed of Computers: 1.8GHz (My office Desktop)
1.2 ALU (Arithmetic and Logic Unit)
Performs most computational operations.
Typical Micro-Operations (The very basic operations
computers are designed to perform as an electronic
device)
1. Adding two integers (Whole numbers with no
decimal point)
00110111 (decimal 55, 1+2+4+16+32)
+ 00111011 (decimal 59)
------------------
01110010 (decimal 114)
Subtraction is done just like Addition
2. Complementing
Turning 01010111 to 10101000
3. Shifting to left (or to right) by a number of
positions.
Has the effect of multiplying by 2, 4, 8, 16,
32, 64 and so forth. (or the effect of dividing)
00001110 will become 01110000 when shifted
left by three positions, being multiplied by 8.
So, the decimal 14 became 112.
4. Comparing two integers
This is a logical operation.
The EU will perform one of a few predefined
operations based upon the outcome of the comparison.
5. Fetching from and Storing into Main Memory.
An instruction in the Main memory needs to be fetched
in order for the EU to execute it.
Also, a data item stored in the Main memory needs
to be fetched before it can be used as an operand.
6. Data Movement.
Moving an integer from MM to a Register or
from a register to the MM or from a register
to a register.
1.3 Registers:
Faster access than MM
Performing special functions such as
(1) controlling instructions being executed
(2) handling memory addressing and
(3) providing arithmetic capability
or containing certain information such as
the starting address of a program segment or the current
computational results.
General-Purpose Registers
AX: Accumulator Register
Primary accumulator for most arithmetic and
I/O (input/output) operations
BX: Base Register
Used as an index to extend memory addressing
and in arithmetic as well.
CX: Count Register
Used in loop iterations or in shifting bits
left or right.
DX: Data Register
required by some I/O operations and also in
* (Multiplication) and / (division)
Segment Registers
CS: Code Segment
Contains the starting address of a program's
code segment.
DS: Data Segment
Contains the starting address of a program's
data segment.
SS: Stack Segment
Contains the starting address of a program's
stack segment.
The offset of a particular stack element is
contained in the SP (Stack Pointer) register.
ES: Extra Segment
Associated with DI (Destination Index) register,
used for memory indexed addressing for some string
operations.
Pointer Registers
IP: Instruction Pointer
Contains the offset of next instruction to be
executed.
SP: Stack pointer
Contains the offset of a stack element to
be referenced.
BP: Base Pointer
Contains the offset address of a parameter
being passed via the stack
Index (For indexed memory addressing for string
operations)
SI: Source Index (together with DS register)
DI: Destination Index (together with ES register)
2. Main Memory
This is where the computer stores application programs
and data currently being executed.
For proper accessing, elements of the MM have addresses.
2.1 Units of MM
a. bit
The smallest unit that is large enough to contain
one of two values:
zero or one
on or off
true or false
b. Byte
eight consecutive bits are grouped into one "BYTE"
which is large enough to contain one of 256
(which is 2 raised to the power of 8)
Typically, a byte can represent a character (or an
alphabetical letter)
c. Word
For some computers, it is two consecutive bytes.
But for some others, it is four consecutive bytes.
In either case, a word typically represents an
integer or a floating-point number (with a decimal
point) like 123.45 or 365.0
A "Two-byte" word can represent an integer roughly between
-32768 (2 raised to the power of 15) and 32767.
A "Four-byte" word can, on the other hand, represent an
integer roughly between -2,000,000,000 and 2,000,000,000
2.2 Types of MM
a. RAM (Random access memory): Most MM
Volatile (Information stored will be lost each time
computer's power switch is turned off)
Hence, before turning off the computer, certain
important pieces of information must be saved to
a secondary storage device like the hard disk , Rewritable CD, USB or
3.5" diskette which is not volatile.
Each byte has its own address by which the computer
properly accesses it.
Accessing a byte takes the same amount of access time
regardless of the address, and hence the name.
Typical size: 2 GB (including expanded memory)
b. ROM (Read-Only Memory)
This is a certain portion of the MM that has a fixed
, READ-ONLY, information not to be altered or
rewritten.
Typically, the core of O.S. programs are stored
in the ROM so that it can be readily loaded into the
MM for immediate execution each time the computer
is turned on.
Typical size: 256K bytes
c. Cache: Special portion of RAM for faster access.
(Faster RAM)
About 5 times faster than other RAM.
This is where the computer stores blocks of RAM
space by moving them from RAM in anticipation of frequent access.
Typical size: 512K Bytes
3. Secondary Storage devices
Permanent (non-volatile) storage of information
usually as files.
Slow access.
3.1 Types
3.5" (floppy) diskette: Usually Drice-A or B
Hard disk: Usually drice-C or -D,
fixed location, not movable.
Typical capacity: 150 GB (desktop)
CD-ROM: Usually drive-E
Recently, rewritable drivers let us write onto CD.
typical capacity: 700 mega bytes
USB (Universal Serial Bus): Removable
Typical Capacity: 2 or 4 GB.
3.2 File structure
Files are organized as a hierarchy of "Folders"
or "Directories"
For example, a 3.5" disk may have
3 folders named F1, F2 ana F3 directly underneath
itself.
The folder F1 may have four folders names F11, F12, F13
and F14, and the folder F2 with its own folders F21, F22,
F23, F25 and F25, and so on.
Now, the folfer F11 may have its own folders and some files
inside itself.
Windows XP provides The Windows Explorer for fast access to
individual files and folders.
3.3 Formatting of 3.5" diskette
1. Before a floppy disk can be used, it must be formatted.
Usually, disks are already formatted when purchased.
2. Purposes
a. Magnetically marking the boundaries of tracks
and sectors
b. Creating the disk directory to contain information
about folders and files yet to be created.
Three parts:
Boot Sector
Root Directory
File Allocation Table.
3. Structures
Two sides
80 tracks per side
18 sectors per track
512 bytes per sector
So, a disk has 2*80*18*512 bytes of space,
1,474,560 bytes.
But, 33 sectors (16,896 bytes) are used for the
disk directory.
4. Steps
a. Make sure the "Write-Protect" tab is closed.
b. Insert a diskette with the external label showing
at top.
c. Double click "My Computer" icon.
d. In the Window that shows up, right-click
the Drive-A icon.
e. The shortcut menu of Drive-A will show up.
Click the "FORMAT..." command
f. The Formatting dialog box will display.
In this D.B., you enter your internal
label like "HKOH1371A" or "HKOH1371B" in the text field
labeled "Volume Label."
g. Then, inside the "Format options" box,
you choose "Quick Format" by clicking.
The Quick formatting is allowed only if
the diskette has already been formatted once.
h. Then click "Start" button at the bottom of this
dialog box to start the formatting.
A warning message will appear that says
"Formatting will erase all data ..."
When you see this message, it shows that every
thing is normal. So, you just click the "OK"
button to let the computer to go ahead to
complete the formatting process.
i. When the formatting is complete, you will see
a message "FORMAT COMPLETE"
You can click "OK" button again when you see this.
The computer will let you repeat above four steps,
f,g,h, and i, in formatting other diskettes.