Transcript Computer System Basics 1

Computer System Basics
1
The System Unit
• Bay - a shelf or opening
used for the installation
of electronic equipment
• System unit - houses
the motherboard,
power supply, and
storage devices
• Case - empty box with
just power supply
Overhead view of system unit
2
Computer Architecture
3
Flow of Information
• The parts are connected to one another by a collection of
wires called a bus
4
Memory
• Memory is a collection of
cells, each with a unique
physical address for
random (direct) access
• memory is divided into
fixed-length units or words
• Information that is stored
in memory cells is in
binary coded format:
– Instructions that make up
programs
– Data: text symbols,
numbers, images, etc.
Information Storage
• Kilobyte
approx. 1000 bytes (actually 210 = 1024 bytes)
• Megabyte
approx. 1,000,000 bytes (one million)
• Gigabyte
approx. 1,000,000,000 bytes (one billion)
• Terabyte
approx. 1 trillion bytes
• Petabyte
approx. 1 quadrillion bytes
6
Types of Memory
•
Types of memory chips:
1
2
3
4
RAM
ROM
CMOS
Flash
7
Types of Memory
RAM - Random Access Memory, used to temporarily hold
software instructions and data
2 ROM - Read-Only Memory, which cannot be written on or
erased by the computer user. Contains fixed start-up
instructions
3 CMOS - Complementary metal-oxide semiconductor;
powered by a battery and thus doesn’t lose its contents
when the power is off
4 Flash - can be erased and reprogrammed more than once
1
8
Cache and Virtual Memory
• Cache - temporary storage for instructions and data that
the processor is likely to use frequently, thus speeding up
processing
• Level 1 (L1) cache - built into the microprocessor
• Level 2 (L2) cache - consists of RAM chips outside
microprocessor
• Virtual memory - free hard-disk space used to extend the
capacity of RAM
9
Secondary Storage Devices
• Because most of main memory is volatile and limited, it is
essential that there be other types of storage devices
where programs and data can be stored when they are no
longer being processed
• Secondary storage devices can be installed within the
computer box at the factory or added later as needed
• Examples of secondary storage media:
–
–
–
–
–
Magnetic tape
Magnetic disk (hard disk or floppy disk)
Optical disk (such as CD ROM or DVD ROM)
Zip disks (a type of magnetic media)
External flash memory
10
Magnetic Tape
• The first truly mass
auxiliary storage device
was the magnetic tape
drive
• A magnetic tape drive is
an example of sequential
storage device
– Tape must be rewound
or fast-forwarded to get
to get the correct block
under the read/write
head (similar to tapes
used to record music)
• In contrast, magnetic
disk drives are direct
access devices.
Magnetic Disks
•
•
•
A read/write head travels across a
spinning magnetic disk, retrieving or
recording data
Each disk surface is divided into sectors
and tracks
Example of disk addressing scheme:
surface 3, sector 5, track 4
Compact Disks and DVD
• A CD drive uses a laser to read information stored optically
on a plastic disk
• CD-ROM is Read-Only Memory
• DVD stands for Digital Versatile Disk
– DVD-ROM - for reading only
– DVD-R - for recording on once
– For rewriting many times:
 DVD-RW
 DVD-RAM
 DVD+RW
13
Ports & Cables
•
Types of ports:
1
2
3
4
5
6
Serial port
Parallel port
SCSI port
USB port
Dedicated ports
Infrared port
14
Ports & Cables
• Serial port - sends bits one at a time, one after another
– Used to connect a variety of “serial” devices
– Sometimes used to connect mouse or keyboard
• Parallel port - transmits 8 bits simultaneously
– Used most commonly for printers
– Also used for other “parallel” devices such as external hard drives,
external CD drives, etc.
– Being practically replaced with faster technologies such as USB.
• USB port
– can theoretically connect up to 127 peripheral devices
daisy-chained to one general-purpose port
15
Expandability: Buses & Cards
• Expansion slots- sockets on
the motherboard into
which you can plug
expansion cards
• Expansion cards - circuit
boards that provide more
memory or that control
peripheral devices
• Examples:
–
–
–
Graphics (video) cards
Network cards
Internal modems
16
The Components of System Software
Operating system - the
principal component of
system software
Device drivers - help
the computer control
peripheral devices
Utility programs support, enhance, or
expand existing
programs
17
Structure of the OS
• The operating system shell
includes the user
interface (UI).
• Users only interact with the
OS through the UI.
• The UI can be
– Command/characterbased (e.g., DOS or UNIX)
– Graphical user interface
(GUI), involving windows,
menus, icons, etc.
kernel
kernel - program which remains in main
memory while the computer is running,
and directs other “nonresident” programs
to perform tasks that support application
programs
18
What Is an Operating System?
• The operating system:
–
–
–
A collection of programs that help you use the computer.
Acts as a smart assistant that moves controls the flow of information to
various components and other programs.
Manages the usage, storage, and access of programs, data, and
processes.
Common Tasks Performed by the OS
19
Main Operating System Functions
• Task management
–
preparing, scheduling, and monitoring of tasks for continuous processing
by the CPU
• Memory management
–
allocation of memory for various tasks; transfer of data and programs
from external storage to memory and back; virtual memory management;
cache management
• Device management
–
controlling flow of data to an from input/output devices, and management
of device drivers
• File and data management
–
controlling how files are created, accessed, organized, copied, and
modified; controlling and managing the storage of data in external storage
devices
• System monitoring
–
monitoring of system resources and devices; error detection and recovery
20
Task Management Concepts
• Multi-tasking:
–
–
–
–
Running more than one task (or process) simultaneously.
Each process “stealing” or sharing CPU time.
Such as playing a game while a large document is being printed.
Each process is allocated a CPU time slice; at the end of the time
slice the process in “interrupted” and its “state” is saved until the
CPU can come back to the process; CPU is then allocated to the
next process on the queue.
• Context Switching:
– Switching from one process or one user to another.
– Such as from a word processor to a spreadsheet and back again
(both reside in RAM).
21
Memory Management Concepts
•
•
•
•
At any point in time memory is divided into
a set of partitions, some empty and some
allocated to running processes.
A portion of the memory is always reserved
for the operating system and other system
processes.
When a process is activated, its memory
address (location of the first instruction in
the program) and the total space (length)
for the process are stored the CPU registers.
This way, the CPU will know how to get back
to the process as it switches among different
running processes.
22
Memory Management Concepts
• Cache memory
– If the primary memory were as large as ever needed, the following
ideas would not be necessary.
– Cache memory: Addresses the concerns of speed and efficiency
(two types).


1. Disk cache - saves the most frequently used parts of the program
being run or executed in the RAM memory - it will be there ready to
go (very fast).
2. RAM disk - fools the program into thinking it is accessing the disk,
but instead the needed information has been transferred to RAM
(RAM is much faster than disk access).
23
Memory Management Concepts
• Virtual Memory
– addresses the problem of a program (or multiple programs) being
too big to fit into the available RAM.



The operating system divides the program into pieces.
The pieces are stored on the hard disk.
The pieces are retrieved into RAM as needed.
– Disadvantage: This slows the system down, because retrieval of
information from the disk is time consuming.
24
File Management Concepts
• A file is a named collection of related data
• A file system is the logical view that an operating system
provides so that users can manage information as a
collection of files
• A file system is often organized by grouping files into
directories (Folders)
• Most files, whether they are in text or binary format,
contain a specific type of information
– For example, a file may contain a Java program, a JPEG image, or
an MP3 audio clip
• The kind of information contained in a document is called
the file type
– Most operating systems recognize a list of specific file types
25
File Management Concepts
File Types
•
File names are often separated,
usually by a period, into two
parts
– Main name
– File extension
•
Some common file types and their extensions
The file extension indicates
the type of the file
File Operations
•
•
•
•
Create a file
Delete a file
Open a file
Close a file
•
•
•
•
•
Read data from a file
Write data to a file
Rename a file
Copy a file
Move a file
26
File Management Concepts
• File Protection
– In multi-user systems, file protection is of primary importance
– We don’t want one user to be able to access another user’s files unless the
access is specifically allowed
– A file protection mechanism determines who can use a file and for what
general purpose
• A file’s protection settings in the Unix operating system is divided into
three categories: Owner, Group, World (all users)
27
File Management Concepts
Directory Trees
• A directory of files can be contained within another
directory
– The directory containing another is usually called the parent
directory, and the one inside is called a subdirectory
– The directory at the highest level is called the root directory
• A file system is often viewed as a directory tree
• At any point in time, you can be thought of as working in a
particular location (that is, a particular subdirectory)
– This subdirectory is referred to as the current working directory
28
Example: Directory Tree in Windows
29
Path Names
• A particular file is identified by specifying that file’s path, which is the
series of directories through which you must go to find the file
– An absolute path name begins at the root and specifies each step down
the tree until it reaches the desired file or directory
– A relative path name begins from the current working directory
• Examples of absolute paths:
C:\Program Files\MS Office\WinWord.exe
C:\My Documents\letters\applications\vaTech.doc
C:\Windows\System\QuickTime
• Suppose the current working directory is
C:\My Documents\letters
Then the following relative path name
applications\depaul.doc
Corresponds to the absolute path:
C:\My Documents\letters\applications\depaul.doc
30
System Software - Utility Programs
• Backup utility
–
program which makes a duplicate copy of the information on your hard
disk
• Data-recovery utility
–
program which restores data that has been physically damaged or
corrupted
• Antivirus software
– program that scans hard disks, floppy disks, and memory to detect viruses
• Data compression utility
–
program which removes redundant elements, gaps, and unnecessary data
from a computer’s storage space so that less space (fewer bits) is required
to store or transmit data
• Disk cleanup utilities
–
–
Detect & remove unnecessary files
Detect & correct disk problems
31
System Software - Utility Programs
• Fragmentation - the scattering
of portions of files about the
disk in nonadjacent areas, thus
greatly slowing access to the
files
• Defragmenter utility - program
that finds all the scattered files
on your hard disk and
reorganizes them as contiguous
files
32
Development Software
• Computers can only understand instructions that are in machine
language
–
–
–
Machine language instructions are binary encoded operations that make
up a program
Programmers, however write programs in a high-level language, not in
binary
A special program, called a “translator” needs to be used to convert the
high-level language source code into binary machine code that the
computer understands. The machine code program is called the “object”
program.
• Two types of translators:
–
–
Compilers: translate the whole source code into machine code in one
step. After the translation, the machine code can be executed as a single
program.
Interpreters: translate and execute the source code one statement at a
time. The processing is done interactively.
33
Development Software
The “Compilation” Process
34