1. Computer System Basics

2. Overhead view of system unit
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
FACTOID: A bay which is open to the outside of the PC is termed “accessible” or “exposed.” A bay which is closed inside the PC case is termed “hidden” or “internal.”
Overhead view of system unit

3. Computer Architecture

4. Flow of Information
The parts are connected to one another by a collection of wires called a bus

5. 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.

6. Information Storage
Kilobyte approx 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
FACTOIDs:
The prefix “mega” in “megabyte” comes from the Greek word “megas” meaning “mighty” or “great.”
The prefix “giga” in “gigabyte” comes from a Greek word meaning “giant.”
The prefix “tera” in “terabyte” comes from a Greek word meaning “monster.”
You might think that the largest unit of storage capacity is a petabyte, but in fact, there are also exabytes, zetabytes, and yottabytes.

7. Types of Memory Types of memory chips: RAM ROM CMOS Flash
Volatile - a term used to describe memory in which the contents are lost when the power goes off or is turned off.

8. Types of Memory
RAM - Random Access Memory, used to temporarily hold software instructions and data
ROM - Read-Only Memory, which cannot be written on or erased by the computer user. Contains fixed start-up instructions
CMOS - Complementary metal-oxide semiconductor; powered by a battery and thus doesn’t lose its contents when the power is off
Flash - can be erased and reprogrammed more than once
Read - to transfer data from an input source into the computer’s memory or CPU.
Write - to transfer data from the computer’s CPU or memory to an output device.
FACTOID: “Firmware” is a combination of software and the read-only storage hardware (such as ROM chips) on which it is recorded.

9. 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
Processor searches for data or instructions in the following order: L1 L2
RAM
Virtual memory

10. 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

11. 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.

12. 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

13. 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

14. Ports & Cables Types of ports: Serial port Parallel port SCSI port
USB port
Dedicated ports
Infrared port

15. 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.
Parallel port is third from left on bottom of display.
Parallel ports are faster than serial ports, but can transmit information efficiently only up to 15 feet.
USB port
can theoretically connect up to 127 peripheral devices daisy-chained to one general-purpose port

16. 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

17. 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
Operating system (OS) - the master system of programs that manage the basic operations of the computer. Also called the software platform.

18. 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/character-based (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

19. 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

20. 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

21. 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).

22. 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.

23. 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).

24. 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.

25. 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

26. File Management Concepts
File Types
File names are often separated, usually by a period, into two parts
Main name
File extension
The file extension indicates the type of the file
Some common file types and their extensions
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

27. 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)

28. 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

29. Example: Directory Tree in Windows

30. Path Names Then the following relative path name
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

31. 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
Utilities - programs which perform tasks related to the control and allocation of computer resources.
FACTOID: Now that recordable CDs (CD-Rs) and rewritable CDs (CD-RWs) are becoming more and more common, backup utilities are being created to back up files onto them. Backup NOW! by NTI is one such utility.

32. 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

33. 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.

34. Development Software
The “Compilation” Process