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Computer

-A computer is a fast and accurate electronic programmable device that accepts data and instructions , processes them as the instructions , and produces information as an output.

Computer works when an user feed instrction on computer . when a user feed an instruction to the computer using input device then computer display information as output from output device.

PRIMARY MEMORY

A computer memory is just like a human brain. it is the part of the computer that stores data,information ,instructions or programs either temporarily or permanently. it stores data, instructions, or programs in binary form. The computer system has primary and secondary memory. A primary memory is the internal memory of a computer. it is also known as the main memory. it is a semiconductor based memory that stores or holds fewer amounts of data, instructions and programs. it is a fast memory and the cpu can access the programs or data stored in it directly. it is also called Immedicate Acess Memory. There are two types of primary memory. They are:

i) Read Only Memory (ROM)

-Read Only Memory (ROM) is a chip type internal memory of a computer that is on a Motherboard. it is called CMOS (Complementary Metal Oxide semiconductor). it contains the BIOS (Basic Input Output System) program,which is a bridge between the motherboard and the operating system. The basics program stored in ROM is called firmware. The motherboard manufacture stores the firmware in ROM at the time of motherboard. The firmware stored in ROM can only be read by CPU but can't be erased or rewritten. so, it is also called Read Only Memory.

ii.RAM (Random access memory)

-RAM (Random Access Memory) is the hardware in a computing device where the operating system (OS), application programs and data in current use are kept so they can be quickly reached by the device's processor. RAM is the main memory in a computer. It is much faster to read from and write to than other kinds of storage, such as a hard disk drive (HDD), solid-state drive (SSD) or optical drive. Random Access Memory is volatile. That means data is retained in RAM as long as the computer is on, but it is lost when the computer is turned off. When the computer is rebooted, the OS and other files are reloaded into RAM, usually from an HDD or SSD. Function of RAM Because of its volatility, RAM can't store permanent data. RAM can be compared to a person's short-term memory, and a hard disk drive to a person's long-term memory. Short-term memory is focused on immediate work, but it can only keep a limited number of facts in view at any one time. When a person's short-term memory fills up, it can be refreshed with facts stored in the brain's long-term memory. A computer also works this way. If RAM fills up, the computer's processor must repeatedly go to the hard disk to overlay the old data in RAM with new data. This process slows the computer's operation.

Difference between Ram and Rom

RAM	ROM
Random Access Memory (RAM) has a higher capacity when compared to ROM.	ROM has a lower capacity compared to RAM.
Random Access Memory (RAM) is expensive when compared to ROM.	ROM is cheaper when compared to RAM..
Data in RAM can be modified, erased, or read.	Data in ROM can only be read, it cannot be modified or erased.
The speed of Random Access Memory (RAM) is higher when compared to ROM.	The speed of Read-only Memory (ROM) is slower when compared to RAM.
Data of RAM is very volatile, it will exist as long as there is no interruption in power.	Data present in Read-Only Memory (ROM) is not volatile, it is permanent. Data will remain unchanged even when there is a disruption in the power supply.

Cache memory

-Cache Memory is a special very high-speed memory. It is used to speed up and synchronize with high-speed CPU. Cache memory is costlier than main memory or disk memory but more economical than CPU registers. Cache memory is an extremely fast memory type that acts as a buffer between RAM and the CPU. It holds frequently requested data and instructions so that they are immediately available to the CPU when needed. Cache memory is used to reduce the average time to access data from the Main memory. The cache is a smaller and faster memory that stores copies of the data from frequently used main memory locations. There are various different independent caches in a CPU, which store instructions and data.

virtual memory

-Virtual memory is a common technique used in a computer's operating system (OS). Virtual memory uses both hardware and software to enable a computer to compensate for physical memory shortages, temporarily transferring data from random access memory (RAM) to disk storage.

SECONDARY MEMORY

-The secondary storage devices which are built into the computer or connected to the computer are known as a secondary memory of the computer. It is also known as external memory or auxiliary storage.
The secondary memory is accessed indirectly via input/output operations. It is non-volatile, so permanently stores the data even when the computer is turned off or until this data is overwritten or deleted. The CPU can't directly access the secondary memory. First, the secondary memory data is transferred to primary memory then the CPU can access it.

Difference between primary and secondary memory

primary memory	secondary memory
Primary memory is temporary.	Secondary memory is permanent.
Primary memory devices are more expensive than secondary storage devices.	Secondary memory devices are less expensive when compared to primary memory devices.
Primary memory is directly accessible by Processor/CPU.	Secondary memory is not directly accessible by the CPU.
Primary memory is also known as Main memory or Internal memory.	Secondary memory is also known as External memory or Auxiliary memory.
Examples: RAM, ROM, Cache memory, PROM, EPROM, Registers, etc.	Examples: Hard Disk, Floppy Disk, Magnetic Tapes, etc.

Some of the secondary memory or storage devices are described below:
1) Hard Disk:

It is a rigid magnetic disc that is used to store data. It permanently stores data and is located within a drive unit. Play Video

Secondary Memory
The hard disk is also known as a hard drive. It is a rigid magnetic disc that stores data permanently, as it is a non-volatile storage device. The hard disk is located within a drive unit on the computer's motherboard and comprises one or more platters packed in an air-sealed casing. The data is written on the platters by moving a magnetic head over the platters as they spin. The data stored on a computer's hard drive generally includes the operating system, installed software, and the user's files and programs, including pictures, music, videos, text documents, etc.

Components of Hard Drive:
The main components of a hard drive include a head actuator, read/write actuator arm, read/write head, platter, and spindle. A circuit board, which is called the disk controller or interface board, is present on the back of a hard drive. It allows the hard drive to communicate with the computer.

2) Solid-state Drive:

Secondary Memory
SSD (Solid State Drive) is also a non-volatile storage medium that is used to hold and access data. Unlike a hard drive, it does not have moving components, so it offers many advantages over SSD, such as faster access time, noiseless operation, less power consumption, and more.

As the cost of SSD has come down, it has become an ideal replacement for a standard hard drive in desktop and laptop computers. It is also suitable for notebooks, and tablets that don't require lots of storage.

- 3) Pen drive:

Secondary Memory
Pen drive is a compact secondary storage device. It is also known as a USB flash drive, thumb drive or a jump drive. It connects to a computer via a USB port. It is commonly used to store and transfer data between computers. For example, you can write a report using a computer and then copy or transfer it in the pen drive. Later, you can connect this pen drive to a computer to see or edit your report. You can also store your important documents and pictures, music, videos in the pen drive and keep it at a safe place.
Pen drive does not have movable parts; it comprises an integrated circuit memory chip that stores the data. This chip is housed inside a plastic or aluminium casing. The data storage capacity of the pen drive generally ranges from 2 GB to 128 GB. Furthermore, it is a plug and play device as you don't need additional drives, software, or hardware to use it.

4) SD Card:

Secondary Memory
SD Card stands for Secure Digital Card. It is most often used in portable and mobile devices such as smartphones and digital cameras. You can remove it from your device and see the things stored in it using a computer with a card reader.
There are many memory chips inside the SD card that store the data; it does not have moving parts. SD cards are not created equal, so they may differ from each other in terms of speed, physical sizes, and capacity. For example, standard SD cards, mini SD cards, and micro SD cards.

5) Compact Disk (CD):

Secondary Memory
Compact Disk is a portable secondary storage device in the shape of a round medium disk. It is made of polycarbonate plastic. The concept of CD was co-developed by Philips and Sony in 1982. The first CD was created on 17 August 1982 at the workshop of Philips in Germany.
In the beginning, it was used for storing and playing sound recordings, later it was used for various purposes such as for storing documents, audio files, videos, and other data like software programs in a CD.
Physical characteristics of a CD/ Structure of CD:
A standard CD is around 5 inches in diameter and 0.05 inches in thickness. It is made of a clear polycarbonate plastic substrate, a reflective metallic layer, and a clear coating of acrylic plastic. These thin circular layers are attached one on top of another as described below:
A polycarbonate disc layer at the bottom has the data encoded by creating lands and pits.
The polycarbonate disc layer is coated with a thin aluminium layer that reflects the laser.
The reflective aluminium layer is coated with a lacquer layer to prevent oxidation in order to protect the below layers. It is generally spin coated directly on the top of the reflective layer.
The label print is applied on the lacquer layer, or artwork is screen printed on the top of the disc on the lacquer layer by offset printing or screen printing. How Does a CD Work?
The data or information is stored or recorded or encoded in CD digitally using a laser beam that etches tiny indentations or bumps on its surface. The bump is called a pit, which represents the number 0. Space, where the bump is not created, is called land, and it represents the number 1. Thus, the data is encoded into a compact disc by creating pits (0) and lands (1). The CD players use laser technology to read the optically recorded data.

6) DVD:

Secondary Memory
DVD is short for digital versatile disc or digital video disc. It is a type of optical media used for storing optical data. Although it has the same size as a CD, its storage capacity is much more than a CD. So, it is widely used for storing and viewing movies and to distribute software programs as they are too large to fit on a CD. DVD was co-developed by Sony, Panasonic, Philips, and Toshiba in 1995.

Types of DVDs:
DVDs can be divided into three main categories which are as follows:
DVD-ROM (Read-Only): These types of DVDs come with media already recorded on them, such as movie dvds. As the name suggests, data on these discs cannot be erased or added, so these discs are known as a read-only or non-writable DVD. DVD-R (Writable): It allows you to record or write information to the DVD. However, you can write information only once as it becomes a read-only DVD once it is full. DVD-RW (Rewritable or Erasable): This type of discs can be erased, written, or recorded multiple times.

1.Input Device

A computer user needs to communicate with a computer in order to use the computer. To use the computer , a user need to give the instructions and data using input devices .In computing, an input device is a piece of equipment used to provide data and control signals to an information processing system, such as a computer or information appliance. Examples of input devices include keyboards, mouse, scanners, cameras, joysticks, and microphones.

1.a.keyboard

A keyboard is one of the primary input devices used with a computer. Similar to an electric typewriter, a keyboard is composed of buttons used to create letters, numbers, and symbols, and perform additional functions.

A computer performs the following functions :
i. It accepts or reads the data and instructions from the user.
ii. It converts these input into the computer acceptable forms .

1.b.Mouse

-A computer mouse is a hand-held pointing device that detects two-dimensional motion relative to a surface. This motion is typically translated into the motion of a pointer on a display, which allows a smooth control of the graphical user interface of a computer.

1.c.Touch Pad

-A touchpad or trackpad is a pointing device featuring a tactile sensor, a specialized surface that can translate the motion and position of a user's fingers to a relative position on the operating system that is made output to the screen.Touchpads are a common feature of laptop computers as opposed to using a mouse on a desktop, and are also used as a substitute for a mouse where desk space is scarce. Because they vary in size, they can also be found on personal digital assistants (PDAs) and some portable media players. Wireless touchpads are also available as detached accessories.

1.d.Touch Screen

A touch screen is an electronic display screen that is also an input device. A user interacts with the computer, tablet, smartphone or touch-controlled appliance by using hand gestures and fingertip movements to tap pictures, moving elements or type words on the screen. The screens are pressure-sensitive and can be used or manipulated using fingers or a stylus.

1.e.Digital Computer

-A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital,largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices like smartphones with the same or more capabilities and features of dedicated cameras (which are still available).High-end, high-definition dedicated cameras are still commonly used by professionals and those who desire to take higher-quality photographs.

1.f.Scanner

-A scanner is a device that captures images from photographic prints, posters, magazine pages and similar sources for computer editing and display. Scanners work by converting the image on the document into digital information that can be stored on a computer through optical character recognition (OCR).
There are generally two types of scanner :

i.Handheld Scanner

-A handheld scanner is an electronic device used for scanning physical documents into digital formats. This can thereby be digitally stored, edited, transferred or emailed within the digital network

ii. Flatbed Scanner

-A flatbed scanner is an optical scanner which makes use of a flat surface for scanning documents. The scanner is capable of capturing all elements on the document and does not require movement of the document.

2.Output Device

-All the devices that are used to display or present the result of processing and other information to the user in a human-understandable form are known as output devices.
In other word,An output device is any piece of computer hardware converts information into a human-perceptible form or, historically, into a physical machine-readable form for use with other non-computerized equipment. It can be text, graphics, tactile, audio, or video. Examples include monitors, printers, speakers, headphones, projectors, GPS devices, optical mark readers, and braille readers.

Some of the commonly output devices are:

2.a.Monitor

A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a visual display, support electronics, power supply, housing, electrical connectors, and external user controls.
There are two types of monitor:

i.CRT Monitor

-A CRT (cathode-ray tube) monitor is an analog display device that creates a visible image on the screen by directing three electron beams over millions of phosphor dots to make them light up. In a color monitor, the screen is composed of numerous stripes of alternating red, green, and blue phosphor dots, which get activated by the electrons and combine to make countless different hues.

ii.LCD Monitor

-A liquid crystal display (LCD) monitor is a computer monitor or display that uses LCD technology to show clear images, and is found mostly in laptop computers and flat panel monitors. This technology has replaced the traditional cathode ray tube (CRT) monitors, which were the previous standard and once were considered to have better picture quality than early LCD variants. With the introduction of better LCD technology and its continuous improvement, LCD is now the clear leader over CRT, in terms of color and picture quality, not to mention capabilities for large resolutions. Also, LCD monitors may be made much more cheaply than CRT monitors.

2.b.Speaker

A computer speaker is an output hardware device that connects to a computer to generate sound. The signal used to produce the sound that comes from a computer speaker is created by the computer's sound.

Speakers are usually in a group of two and come in various sizes and shapes. Through the speaker, you can listen to songs that are stored on the hard disk of the computer

2.c.Printer

-A printer is an output device that displays the data and result of processing on paper. in other words,computing, a printer is a peripheral machine which makes a persistent representation of graphics or text, usually on paper.

Difference between impact and non-impact printers

Impact printer	Non-Impact printer
Impact printers produce characters and images on a piece of paper by striking it.	A printer prints text and drawings on paper without striking the paper.
Impact printers produce high-level noise	Non-impact printers produce low-level noise.
These are low-speed printers and consume a lot of time.	These are very fast printers as they can print many pages in a minute.
These are generally less expensive.	Non-impact printers are more expensive compared to impact printers.
Impact printers use old printing technology.	Non-impact printers use the latest printing technology.

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HARDWARE INTERFACES
Many peripheral devices can be connected to a computer through the available hardware interfaces. A hardware interface is the connection point or port through which a peripheral device can be connected to the computer. A computer system may have serial port, parallel port, t USB port, HDMI port, PS-2 keyboard port, PS-2 mouse port, VGA port or expansion slot.

Serial port

A serial. port is the serial communication interface through which 1 bit of data can be transferred. It is a 9 pin interface port. It is commonly used to connect a mouse and modem. It can be used to connect two computers in order to transfer Large files between them.

Parallel port

A parallel port is a type of interface that connects an external device, such as printer, scanner or Zip disk drive. It is 25 pin connector (DB-25). The parallel port is also known as the Centronics port. It can transfer 8 bits of data simultaneously. Due to the use of universal serial bus (USB) devices, nowadays the use of parallel port has decreased.

USB Port

A universal. serial bus (USB) port is the most commonly used interface in the computer system nowadays. It can support a maximum of 127 external devices at a time on a computer. It is used for connecting peripheral devices like keyboard, mouse, digital camera, printer, scanner, etc. to a computer in order to communicate. It also provides electric power to external devices such as cooling tans, speaker, etc. It allows a user to connect or disconnect peripheral devices from a computer while the computer is on.

Firewire

It is the high speed serial bus for data communication. It is used for connecting high speed devices like audio/ video equipment, aeroriauticat cemes, medical equipment, etc. It can tr ansfer 4U3 MB of data per second. It can support up to b3 external devices at a time on a single computer.