Printing Devices

Overview of Printers - Categorizing Printers

• Printers fall into two categories:
  
  Impact printers use a device to strike an inked ribbon, pressing ink from the ribbon onto the paper.
  
  Non-impact printers use different methods to place ink (or another substance) on the page.
  
  
  

Dot Matrix Printers -
How Do Dot Matrix Printers Work?

• Dot matrix printers are a common type of impact printer.
  

• A dot matrix printer's print head contains a cluster of pins. The printer can push the pins out to form patterns in rapid sequence.
  

• The pins press an inked ribbon against the paper, creating an image.
  

Dot Matrix Printers - Performance

• Lower-resolution dot matrix printers use nine pins. Higher-resolution models have 24 pins.
  
• Speed is measured in characters per second (cps). Some dot matrix printers print 500 cps.
  
  

Ink Jet Printers –
How Do Ink Jet Printers Work?

• Ink jet printers are an example of non-impact printers.
• The printer sprays tiny droplets of ink onto the paper.
  
  Ink jet printers are available for color and black-and-white printing.
  
  
  

Ink Jet Printers - Performance

Ink jet printers offer speeds of (2 – 4 pages per minute ppm) and resolution (300 – 600 dots per inch dpi), comparable to low-end laser printers.Ink jet printers are inexpensive and have low operating costs.

Laser Printers –
How Do Laser Printers Work?

• Laser printers are non-impact printers.
  They use heat and pressure to bond particles of toner to paper.
  Laser printers are available for color and black-and-white printing.
  
  
  

Laser Printers - Performance





• Laser printers provide resolutions from 300 – 1200 dpi and higher.
  
• Black-and-white laser printers usually produce 4 – 16 ppm.
  
  Laser printers produce higher-quality print than ink jet printers, but are more expensive.
  




Overview of Printers - Evaluating Printers

When evaluating printers, consider four criteria:

Image quality – Measured in dots per inch (dpi). Most printers produce 300 – 600 dpi.

Speed – Measured in pages per minute (ppm) or characters per second (cps)

Initial cost – Consumer printers cost $250 or less, but professional printers can cost thousands of dollars.

Cost of operation – This refers to the cost of supplies used by the printer.

Photo printers



1.Used to print images that can be created by using Digital camera or scanner.




Thermal – Wax printer



1.Presentation Graphics and handouts

2.Bold colors with heavy color requirement, posters or book covers

3.Ribbon coated with panels of colored Wax that melts and adheres to plain paper as colored dots when passed over a focused heat source.



Dye – Sublimation printers



1.Get Realistic quality and color for photo images- Desktop publishers, artist

2.Ribbon containing panels of color is moved across a focused heat source

3.Capable of subtle temperature variations.

4.The heated dyes evaporated from the ribbon and diffuse on specially coated paper .

5.The variation to the color are related to the intensity of the color applied.

6.Create sharp images. Slow.






Plotters



1.Same like printer except that it is used to print large format images – construction drawings created by an architect.

2.Early plotter : Mechanical device contains robotic arm used to draw images on paper




3.Table plotter : Two robotic arms contains colored ink pens

4.Two arms operating at right angles as they draw on a stationary paper

5.Large and complex table plotters are notoriously slow

6.Large complicated drawings can take several hours to print



Roller plotter – Drum plotter



1.one drawing arm but moves the paper

2.The drawing arm moves side to side as the paper is rolled back and forth

3.Draw perfect circles and other geometric shapes.

4.Mechanical plotters replaced by Thermal, electro static, ink jet plotters and dye – sub printers.

5.These devices can also produces large size drawings are faster and cheaper than mechanical plotters

System Software

System ↔ System ↔ Application ↔ Computer

User         Software        Software          System

System s/w is a collection of programs designed to operate, control and extend processing capabilities of computer and which makes the operation of a computer system more effective and efficient.

It comprises of
1.Operating system
2.Device driver
3.System utility
4.Language translators

Operating System

A collection of programs used to control and coordinate the computer system. It manages functions performed by hardware, I/O devices, CPU, Secondary storage devices, communication and n/w equipment.

Functions of operating system:

1.Memory management: It allocates and deallocates the memory of user prg.

2.Process management: Manages prg in execution. It schedules CPU and shares the CPU among many processes.

3.File management: Manages organization, naming, storing, retrieving, sharing and protection of
files.

4.Device management: Controls all the I/O devices and provides flexible and easy interface.

5.Security management: Protects the system resources and information against destruction and unauthorized access.

6.User Interface: It allows the user to give inst. And retrieve info. From the system.

Device Driver

• Special programs to extend the ability of OS in order to support I/O devices such as keyboard, mouse, monitor, printer…
  
• It contains all possible device dependent codes.
  
• It accepts request from device, translate it into commands for the appropriate device controller.
  

             Computer System    ↔  Device Driver  ↔   I/O Device
                                                         

• System utility
  

  • 
    
• Small prg having specific tasks to perform which helps the user maintenance of system
  
  

  • Functions of system utility:
    

  
  1.File management
  
  2.Backup
  
  3.Data recovery
  
  4.Virus protection
  
  5.Disk management
  
  6.Firewall
  
  7.Disk cleanup
  
• 
  
• Language Translator
  
  

  Tool that translates a programming language to m/c language which is understandable by a computer. 
  
  
  
  Categories of translators: 
  

  
  1.Compiler: Converts high level language to m/c level lang.
  or it converts source code (prg) into object code (binary form) as a whole. Compiler is unique for each lang.
  
  2.Interpreter: It converts source code (prg) into object code (binary form) as well as executes it line by line. It executes the statement before translating next statement.
  
  3.Assembler: Converts assembly lang prg into m/c lang prg.

  
  
  

  Flowchart of Compiler
  
  
      
  
  

  Flowchart of Interpreter
  
  

  
  

     
  
  

  Process of Assembler
  

  
  
  

  
  

  
  

    
  
  
  

  
  

  
  

  Types of OS
  
  
  

    
  
  
  

  
  

  
  
• 
  
• 
• 
  

PROCESSING DEVICE - Notes

This topic includes the following sections:
• How Computers Represent Data
• How Computers Process Data
• Factors Affecting Processing Speed

How Computers Represent Data

•Binary Numbers
•The Binary Number System
•Bits and Bytes
•Text Codes

How Computers Represent Data
– Binary Numbers

•Computer processing is performed by transistors, which are switches with only two possible states: on and off.
•All computer data is converted to a series of binary numbers– 1 and 0. For example, you see a sentence as a collection of letters, but the computer sees each letter as a collection of 1s and 0s.
•If a transistor is assigned a value of 1, it is on. If it has a value of 0, it is off. A computer's transistors can be switched on and off millions of times each second.

How Computers Represent Data - Bits and Bytes

•A single unit of data is called a bit, having a value of 1 or 0.
•Computers work with collections of bits, grouping them to represent larger pieces of data, such as letters of the alphabet.
•Eight bits make up one byte. A byte is the amount of memory needed to store one alphanumeric character.
•With one byte, the computer can represent one of 256 different symbols or characters.

How Computers Represent Data - Text Codes

A text code is a system that uses binary numbers (1s and 0s) to
represent characters understood by humans (letters and
numerals).

•An early text code system, called EBCDIC, uses eight-bit codes, but is used primarily in older mainframe systems.
•In the most common text-code set, ASCII, each character consists of eight bits (one byte) of data. It specifies characters for values from 0 to 127. Extended ASCII specifies characters for values from 128 to 255. ASCII is used in nearly all personal computers.
•In the Unicode text-code set, each character consists of 32 bits (four bytes) of data. Mostly all characters used in world like chinese, korean and japanese and mathematical symbols can be represented

How Computers Process Data

Where Processing Occurs:
•The Control Unit
•The Arithmetic Logic Unit
•Machine Cycles
•The Role of Memory in Processing
•Types of RAM

How Computers Process Data –
Where Processing Occurs

•Processing takes place in the PC's central processing unit (CPU).
•The system's memory also plays a crucial role in processing data.
•Both the CPU and memory are attached to the system's motherboard, which connects all the computer's devices together, enabling them to communicate.

The Control Unit

The two main parts of a CPU are the control unit and the arithmetic logic unit (ALU)
•The control unit directs the flow of data through the CPU, and to and from other devices.
•The control unit stores the CPU's instruction set, which contains the list of instructions for all the tasks the CPU can perform.
•Each instruction is expressed in microcode a series of basic directions that tell the CPU how to execute more complex operations.

The Arithmetic Logic Unit

•The actual manipulation of data takes place in the ALU.
•The ALU can perform arithmetic and logic operations.
•The ALU is connected to a set of registers—high speed memory locations built directly in to the CPU that are used to hold data and program instructions currently being processed.

Machine Cycles

To execute each instruction, the CPU follows a series of
steps-called a machine cycle. The machine cycle includes
two smaller cycles.
1.Instruction cycle
Fetching :Before the CPU can execute an instruction, the
control unit must retrieve a command or data from
memory
Decoding: Before execution, CU break down the command into instruction that corresponds to those in the instruction set.
2. Execution cycle
Executing: When the command is executed, the CPU
carries out the instruction by converting them into
microcodes.

Storing: CPU may be required to store the results of an instruction in memory.
•CPU performance is measured in MIPS and BIPS.
•By using a technique called pipelining, many CPUs can process more than one instruction at a time.
•Multitasking by hyperthreading.

There are two basic types of RAM: static and dynamic
• Dynamic RAM (DRAM) chips must be recharged
with electricity very frequently, or they will lose their
contents. One transistor per bit, slower, cheaper,
larger capacity
• Static RAM (SRAM) does not need to be recharged
as often as DRAM, and can hold its contents longer.
To store and retrieve data CPU uses Memory address a number that indicates a location on the memory chip.

The Role of Memory

vNonvolatile memory: Permanent. ROM
§PROM chip ->Chip that cannot be changed .Used in printer and hard drives.
§ROM contains a set of start up instruction->BIOS.
§BIOS contains POST to ensure that the system is functioning properly and all expected hardware devices are present.

Flash memory: Special type of nonvolatile memory used in portable digital devices like digital camera, portable MP3 player, USB.
Volatile memory: Non permanent. RAM
Single in line memory module, Dual in line memory module

Factors Affecting Processing Speed

• Registers
• RAM
• The System Clock
• The Bus
• Cache Memory

Factors Affecting Processing Speed – Registers

•The CPU contains a number of small memory areas, called registers, which store data and instructions while the CPU processes them.
•The size of the registers (also called word size) determines the amount of data with which the computer can work at a one time.
•Today, most PCs have 32-bit registers, mean the CPU can process four bytes of data at one time. Register sizes are rapidly growing to 64 bits.

Factors Affecting Processing Speed – RAM

•The amount of RAM in a PC has a direct affect on the system's speed.
•The more RAM a PC has, the more program instructions and data can be held in memory, which is faster than storage on disk.
•If a PC does not have enough memory to run a program, it must move data between RAM and the hard disk frequently. This process, called swapping, can greatly slow a PC's performance.
•Process of swapping unused content of RAM to hard disk is called Virtual memory

The System Clock

•A single "tick" of the clock is the time required to turn a transistor off and back on. This is called a clock cycle.
•Clock cycles are measured in Hertz (Hz), a measure of cycles per second. If a computer has a clock speed of 300 MHz, then its system clock "ticks" 300 million times every second.
•The faster a PC's clock runs, the more instructions the PC can execute each second.

The Bus

•A bus is group of parallel wires. Each wire can transfer one bit at a time.
•Data bus is an electrical path between the components of a computer. Data and instructions travel along this bus.
•The data bus' width determines how many bits can be transmitted between the CPU and other devices.

•The address bus runs only between the CPU and RAM, and carries nothing but memory addresses for the CPU to use.
•Peripheral devices are connected to the CPU by an expansion bus.

Cache Memory

•Cache memory is high-speed memory that holds the most recent data and instructions that have been loaded by the CPU.
•Cache is located directly on the CPU or between the CPU and RAM, making it faster than normal RAM.
•CPU-resident cache is called Level-1 (L1) cache. External cache is called Level-2 (L2) cache. Cache present resident as well as external to CPU is called Level-3(L3) cache.
•The amount of cache memory has a tremendous impact on the computer's speed.

X= (A+B) * (C+D)
RISC Processor- Reduced instruction set computing
Instruction set is small and the instruction is simple.
Y=A+B
Z=C+D
X=Y*Z
CISC Processor–Complex instruction set computing
Instruction set is large and the instruction is complex.
X= (A+B) * (C+D)

STORAGE DEVICE - Notes

This lesson includes the following sections:
• Categorizing Storage Devices
• Magnetic Storage Devices
• Optical Storage Devices


Categorizing Storage Devices

•Storage devices hold data, even when the computer is turned off.
•The physical material that actually holds data is called a storage medium. The surface of a floppy disk is a storage medium.
•The hardware that writes data to or reads data from a storage medium is called a storage device. A floppy disk drive is a storage device.
•The two primary storage technologies are magnetic and optical.

The primary types of magnetic storage are:

•Diskettes (floppy disks)
•Hard disks
•High-capacity floppy disks
•Disk cartridges
•Magnetic tape

The primary types of optical storage are:

•Compact Disk Read-Only Memory (CD-ROM)
•Digital Video Disk Read-Only Memory
(DVD-ROM)
•CD-Recordable (CD-R)
•CD-Rewritable (CD-RW)
•PhotoCD

Magnetic Storage Devices

• How Magnetic Storage Works
• Formatting
• Disk Areas
• Diskettes
• Hard Disks
• Disk Capacities
• Other Magnetic Storage Devices

Magnetic Storage Devices
- How Magnetic Storage Works

•A magnetic disk's medium contains iron particles, which can be polarized—given a magnetic charge—in one of two directions.
•Each particle's direction represents a 1 (on) or 0 (off), representing each bit of data that the CPU can recognize.
•A disk drive uses read/write heads containing electromagnets to create magnetic charges on the medium.

Magnetic Storage Devices - Formatting

•Before a magnetic disk can be used, it must be formatted—a process that maps the disk's surface and determines how data will be stored.
•During formatting, the drive creates circular tracks around the disk's surface, then divides each track into sectors.
•The OS (Operating System) organizes sectors into groups, called clusters, then tracks each file's location according to the clusters it occupies.

Magnetic Storage Devices - Disk Areas

When a disk is formatted, the OS creates four
areas on its surface:

•Boot sector – stores the master boot record, a small program that runs when you first start (boot) the computer
•File allocation table (FAT) – a log that records each file's location and each sector's status
•Root folder – enables the user to store data on the disk in a logical way
•Data area – the portion of the disk that actually holds data

Magnetic Storage Devices - Diskettes

•Diskette drives, also known as floppy disk drives, read and write to diskettes (called floppy disks or floppies).
•Diskettes are used to transfer files between computers, as a means for distributing software, and as a backup medium.
•Diskettes come in two sizes: 5.25-inch and 3.5-inch.

Magnetic Storage Devices - Hard Disks

•Hard disks use multiple platters, stacked on a spindle. Each platter has two read/write heads, one for each side.
•Hard disks use higher-quality media and a faster rotational speed than diskettes.
•Removable hard disks combine high capacity with the convenience of diskettes.

Magnetic Storage Devices - Disk Capacities

•Diskettes are available in different capacities, but the most common store 1.44 MB.
•Hard disks store large amounts of data. New PCs feature hard disks with capacities of 10 GB and higher.

Magnetic Storage Devices - Other Magnetic Storage Devices

•High-capacity floppy disks offer capacities up to 250 MB and the portability of standard floppy disks.
•Disk cartridges are like small removable hard disks, and can store up to 2 GB.
•Magnetic tape systems offer very slow data access, but provide large capacities and low cost.

Optical Storage Devices

• How Optical Storage Works
• CD-ROM
• CD-ROM Speeds and Uses
• DVD-ROM
• Other Optical Storage Devices

Optical Storage Devices –
How Optical Storage Works

•An optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data.
•To store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected differently.
•When an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value of 0 (off). A land reflects light back to its source, representing a bit value of 1 (on).

Optical Storage Devices –
CD-ROM

•In PCs, the most commonly used
optical storage technology is called
Compact Disk Read-Only Memory (CD-ROM).
•A standard CD-ROM disk can store up to 650 MB of data, or about 70 minutes of audio.
•Once data is written to a standard CD-ROM disk, the data cannot be altered or overwritten.

Optical Storage Devices –
CD-ROM Speeds and Uses

•Early CD-ROM drives were called single speed, and read data at a rate of 150 KBps. (Hard disks transfer data at rates of 5 – 15 MBps).
•CD-ROM drives now can transfer data at speeds of up to 7800 KBps. Data transfer speeds are getting faster.
•CD-ROM is typically used to store software programs. CDs can store audio and video data, as well as text and program instructions.

Optical Storage Devices - DVD-ROM

•A variation of CD-ROM is called Digital Video Disk Read-Only Memory (DVD-ROM), and is being used in place of CD-ROM in many newer PCs.
•Standard DVD disks store up to 9.4 GB of data—enough to store an entire movie. Dual-layer DVD disks can store up to 17 GB.
•DVD disks can store so much data because both sides of the disk are used, along with sophisticated data compression technologies.

Optical Storage Devices - Other Optical Storage Devices

•A CD-Recordable (CD-R) drive lets you record your own CDs, but data cannot be overwritten once it is recorded to the disk.
•A CD-Rewritable (CD-RW) drive lets you record a CD, then write new data over the already recorded data.
•PhotoCD technology is used to store digital photographs.

INPUT DEVICES - Notes.

Standard Methods of Input

This Topic includes the following sections:
· The Keyboard
· The Mouse
· Variants of the Mouse

The Keyboard

•The Standard Keyboard Layout
• Ergonomic Keyboards
• How a Keyboard Works

The Keyboard - Standard Keyboard Layout

•A standard computer keyboard has about 100 keys.
•Most keyboards use the QWERTY layout, named for the first six keys in the top row of letters.

The Keyboard - Standard Keyboard Layout

Most keyboards have keys arranged in five groups:


1. Alphanumeric keys

2. Numeric keypad

3. Function keys

4. Modifier keys
5. Cursor-movement keys

Ergonomic Keyboards

•Ergonomics->Study of Physical relationship between people and their tools.
•Long periods of keyboard use can cause injuries.
•An ergonomically correct keyboard can help you avoid repetitive stress (strain) injuries (RSI).
•You also can avoid injuries by adopting correct keyboarding practices.

The Keyboard - How a Keyboard Works

When you press a key:

•The keyboard controller detects the keystroke.
•The controller places a scan code in the keyboard buffer, indicating which key was pressed.
•The keyboard sends the computer an interrupt request, telling the CPU to accept the keystroke.

The Mouse - What is a Mouse?

•The mouse is a pointing device. You use it to move a graphical pointer on the screen.
•The mouse can be used to issue commands, draw, and perform other types of input tasks.

Variants of the Mouse

•Trackballs
•Trackpads
•Integrated Pointed Devices

Types of Mouse

1.Mechanical Mouse
2.Optical Mouse (Non mechanical)

Mouse Function (Mechanical)

Mouse movesà Mouse ball spins the rollerà Roller gives information to the system softwareà System software controls the pointer

Mouse Function (Optical)

Mouse emits a beam of light-> From the Reflected light distance, direction and speed of pointer is evaluated-> System software controls the pointer

The Mouse - Mouse Techniques


Using the mouse involves five techniques:

1.Pointing; Move the mouse to move the on-screen pointer.
2.Clicking; Press and release the left mouse button
once.
3.Double-clicking; Press and release the left mouse
button twice.
4.Dragging; Hold down the left mouse button as you
move the pointer.
5.Right-clicking; Press and release the right mouse button.

Variants of the Mouse - Trackballs

•A trackball is like a mouse turned upside-down & needs less working space.
•Use your thumb to move the exposed ball and your fingers to press the buttons.

Track pads

•A trackpad is a touch-sensitive pad that provides the same functionality as a mouse.
•To use a trackpad, you glide your finger across its surface.
•Trackpads provide a set of buttons that function like mouse buttons.

Integrated Pointing Devices

•An integrated pointing device is a small joystick built into the keyboard between G and H.
•To use an integrated pointing device, you move the joystick.
•These devices provide a set of buttons that function like mouse buttons

Alternative Input Devices –
Devices for the Hand

• Pens
• Touch Screens
• Game Controllers

Devices for the Hand - Pens

•With a pen-based system, you use an electronic pen called as stylus to write on the screen and choose commands.
•Pens are common input devices for handheld computers, like personal digital assistants (PDAs) and tablet PC for collecting database
•Pens are handy for making notes or selecting commands, not for inputting a lot of text.

Devices for the Hand - Touch Screens

•Touch-screen systems accept input directly through the monitor.
•Touch screens use sensors to detect the touch of a finger. They are useful where environmental conditions prohibit the use of a keyboard or mouse.
•Touch-screen systems are useful for selecting options from menus.
•They are useful for ATM, information centre like railways, departmental stores etc.

Devices for the Hand - Game Controllers

•Game controller is an input device which accepts i/p from the user, process it, and produce o/p in the form of graphics and sound
•The two primary types of game controllers are joysticks and game pads.
•Game pads usually provide controls for each hand. They are flexible and used to control games
•Joysticks are popular for flight simulator and driving games. Some type includes steering wheel, gearshifts and foot pedals


Alternative Input Devices –
Optical Input Devices


•Bar Code Readers
•Image Scanners and OCR (Optical Character Recognition)

Optical Input Devices - Bar Code Readers

•Bar code readers can read bar codes—patterns of printed bars to identify the product.
•The reader emits light, which reflects off the bar code.
A light sensitive detector identifies the bar code image by recognizing special bars at both ends of the image.
•They tells the reader whether the barcode has been read right side up or upside down. Then it converts the individual bar patterns into corresponding code. Then the reader feeds the data into the computer.
•Flatbed bar code readers are commonly found in library, supermarkets. Courier services often use handheld readers.

Optical Input Devices :Image Scanners and OCR

•Image scanner convert any printed image into electronic form by shining light onto the image and sensing the intensity of light reflection at every point.
•Thus they digitize printed images for storage and
manipulation in a computer.
•Color scanners use filters to separate the components of color into the primary additive color (RGB)
•After scanning, when it is a photo we can use photo shop application to change the properties of picture like adjusting contrast, changing color etc.

•Scanners come in a range of size from hand held model to flat bed scanners that sit on desktop.`
•Hand held scanners or portable but require multiple passes to scan a single page because they are not wide as paper.
•Flat bed scanners offered high quality reproduction since it can scan a page in single pass (Xerox m/c).
•Some medium sized scanners are also available (FAX m/c).

OCR
•When it is a text document we can use Optical character recognition (OCR) software to translate scanned text into editable electronic documents.
•Image is first stored as bit map. A bit map is grid of dots, each dot is represented by one or more bits.
•OCR translate the array of dots into letters and numbers.
•For that, it looks at each character and tries to match the character with its own assumption. OCR extremely complex and not 100% accurate.
•It is used to convert the fax into editable document.

Alternative Input Devices –
Audio-Visual (Multimedia) Input Devices

• Audio input àMicrophones and Speech Recognition
• Video Input àPC video camera, Digital camera

Microphones and Speech Recognition

•Microphones can accept auditory input. A microphone requires a sound card in the PC.
•A sound card is a special device which translate analog sound signal from the microphone into digital codes the computer can store and process .This process is called digitizing. Vice-versa can also be done by sound card.
•By this we can record our voice and store it as file in computer. We can use it in presentations, webpages or email it to others.
•With speech recognition software (voice recognition), you can use your microphone to dictate text, navigate programs, and choose commands.

•SRS takes the smallest individual sound in a language called phonemes, and translate them into text.
•Some problem occurs are
1.Differentiating sound for eg: during the process of two and too.
2. To isolate background noise.
3. Need of pause between words.
• Newer software overcome these problems by training with speech patterns and pronunciation.
•Other types of audio i/p are CD, tape player, radio…
MIDI-Musical Instrument Digital interface
A MIDI port or adapter is used to connect the musical instruments to computer.

Video Input

•Applications like video conferencing and video chat needs video files to be communicated between computers.
•PC video cameras digitize full-motion images and can transmit them in n/w. eg:webcam
•It breaks images into pixels and each pixel’s color and characteristics are stored as digital code.
•Video capture card is used to connect video devices to PC.
•Digital cameras are portable, handheld device that capture still images.
•Difference between normal film camera and digital camera.
•Video images may be compressed to use less memory and storage space for passing in network.