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INPUT/OUTPUT DEVICES

Many peripheral devices have the capability of being used as Input and Output devices both. Some of the popular I/O devices are listed below:

Fax Machine:- The fax machine translates a document into a series of zeros and ones (also known as a bit map) that can be transferred like normal computer data. On the receiving side, a fax machine receive the incoming data, translates the zeros and ones back into dots, and reprints the pictures. Thus serve as both Input and Output Devices.

Mulitifunctional Devices (MFD):- It is a device that perform a variety of functions that would else be carried out by separate peripheral devices. A multifunction periphereal combine a minimum two of the following: a printer, a scanner, and a copier. Example of such device is a Multi-Functional Printer.

Modem:- It is a device which converts Analog signals received over the telephone line to Digital signal which may be used as Input for a Computer. Similarly it transmits information received from a computer over the telephone lines.

Touch screen displays and digital camera are few other examples of common input/output devices.

Computer Memory:- A computer memory is just like a human brain. It is used to store data and information. Computer memory is the storage space where data and instructions which are to be processed are kept. Memory is primarily of three types: cache Memory, Primary Memory / Main Memory and Secondary Memory.

Cache Memory:- Cache memory is a very high speed semi-conductor memory which may speed up the CPU and the main memory. It is used to contain those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transmitted from disk to cache memory by operating system from where CPU can access them. The following are the advantages of cache memory

1. Cache memory is faster than the main memory

2. It consrumes less access time as compared to main memory

3. It stores data for temporary use

4. It stores the program that can be stored within a short period of time

There are certain disadvantages of cache memory:

1. Cache memory has limited capacity

2. It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which computer is working currently. The data in this memory is lost when the power is off. This memory is generally made up of semiconductor deivces. It means intergrated circuits consisting of silicon based transistors. RAM (Random Access Memory) and ROM (Read Only Memory) are two examples of main memory. RAM is volatile memory. Samles of non-volatile memory are ROM/ PROM (Programmable)/ EPROM (Erasable PROM) and flash memory. The data and instructions required to be processed reside in the main memory. RAM and ROM are two examples of main memory. Additional characteristics of main memory are:

1. It is the working memory of the computer.

2. Its speed is faster than the main memory.

3. A computer cannot run without primary memory

Random Access Memory (RAM)

The read and write (R/W) memory of computer is called computer memory. The user can read as well as write information to it. with RAM any location can be reached after specifying the address of the location. RAM is considered "random make up the individual storage canlls which can each remember an amount of data. There are two types of basic RAMs:

a. Dynamic RAM (DRAM)

b. Static RAM (SRAM)

The term static differentiates SRAM from DRAM which must be periodically refreshed. SRAM is faster and more costly than DRAM; it is commonly used for CPU cache while DRAM is used for a computer's main memory. Some other forms of RAM are:

a. EDO (Extended Data Output): RAM- in EDO, any memory lacation cab be accessed. It stories 256 bytes of data information in latches.

b. SDRAM (Synchronous DRAMs): These RAM chips use the same clock rate as the CPU uses.

c. DDR-SDRAM (Double Data Rate- SDRAM): This Ram transmits data on both edges of the clock.

Read Only Memory (ROM)

It is non-volatile memory. The information stored on it is not lost, even when power goes off. It is used for permanent storage of information. The information on ROM cannot be ahered. Whatever is stored on it by the manufacturer. it remains fixed.

The following are the types of ROMs:

a. PROM: It is programmable Read Only Memory. Its contents are decided by the user. The user can store permanent programs. The data is fed into it using PROM programs.

b. EPROME: It is an erasable PROM. The stored information on EPROM's can be erased by exposing it to UV rays in about 15 minutes. It is not possible to erase a part of it, but the entire contents are to be removed. EPROM's are cheap and reliable.

c. Flash Memory: It is an electrically erasable and programmable permanent type of memory. It uses transistor memory, all resulting in high packing density, low power consumption, low cost and higher reliability. It is used in digital cameras, MP3 players.

Secondary Memory

Secondary Memory is also known as external memory or non-volatile memory. It is slower than the main memory. It is used for storing data and information permanently. CPU does not access secondary memory directly; rather they are retrieved via input-output routines. Contents of secondary memory are first transferred to main memory, and then CPU can access it.

Characteristics of Secondary Memory:

1. These are optical and magnetic memories. ( Used as Back Up Memory )

2. Data is permanently stored , even when the power is switched off. (non-volatile memory)

3. Slower than primary memories.

4. Large and voluminous data may be stored without much cost involvement.

Hard Disk, Hard Drive

It is a data storage device used for storing and retieving digital infromation using one or more fast rotating disks covered with magnetic material. Theplatters are paired with magnetic heads arranged on a moving arm, which read and write information to the platter surface. Data is accessed in a random access manner that means the data can be accessed in any sequence. An HDD retains its data even when the power is off.

The Primary characteristics of HDD are its capacity and performance. A terabyte (TB) drive has a capacity of 1000 gigabyte (GB) where 1 GB=1 billion bytes. Performance is specified by the time raken by it to retrieve the data i.e. the data rate.

Optical Disks

All optical disks are circular shaped platters. These come in different size and storage capacity. The most popular optical disk types are WORM (CD-R), CD-RW, DVD and Blu-Ray Discs.

WORM Disk/CD Recordable Disk

WORM Means Write Once, Read Many Disks or Compact Disc-Rrcordable (CD-R). Using a CD recording drive one can store data on WORM Disk/CD-R Disks only once. Data in these disks are written by creating pits on the surface by shining a laser for reading.

Compact Disc-Read/Write (CD-RW)

It is simimilar to a WORM Disk however you can wipe out and re-write the information multiple times.

Digital Versatile Disc (DVD)

It is an optical storage device that looks same as CD with a storage capacity up to 4.7 GB-8.5 GB of data. DVD's may be classified as single layer disk or double layer disk. It is most popularly used for storing high quality movies and audio files.

Blu-Ray Disc

It is expected to replace existing DVD's in the future. These discs also use a laser beam for recording with the additional capability to store high density data. It has capacity varying from 50 GB to 500 GB.

Pen Drive/Flash Memory

It uses a small portable device which can be connected to a computer through USB Port. It can retain data even when it is not connected to a computer. It is very easy to disconnect and carry anywhere safely.

SmartMedia Card

It's most popularly being used in Digital Camera these days and is like a portable credit card.

Secure Digital Card (SD Card)

They are second generation Multimedia Card. It has the ability to lock and protect the data from being used. It has two variants:

Minisd Card: this is used to meet the requirements storing data in smart phones.

MicroSD Card: It is smaller than MiniSD Memory card with all the features as available in MiniSD.

Computer Classification

Computers may be classifed based on their data processing capabilities. they are categorized according to purpose, data handling, funtionality, size storage capacity and performance.

Classification based on Operationg Principles

According to operating principles and data hangdling, computers can be classified into following three catergories: Analog, Digital and Hybrid Computers.

Analog Computer

Analog computers work on the principles of measuring, in which the measurements gained are translated into data. These are used to measure quantities like voltage, temperatures, current etc. These computers do not operate on numbers directly.

Digital Computers

These computers operate with information in the digital form. These computers operate with more accuracy and faster rate. These operate by counting. these computers are used for all general purpose application and are used for voluminous data processing work.

Hybrid Computers

These computers exhibit features of both digital and Analog computers. A hybrid computers system setup offers a cost effective method of performing complex simulations. These computers serve as controller and provide logical operation.

Classification based on Size, Storage Capacity and Performance

Computers can be very big as large as a big room and as small as a laptop or a micro controller in a mobile and embedded system. The four basic type of computers are Supter, Mainframe, Mini amd Micro Computer.

Supter Computer

These are the most powerful computers in terms of data storage, perfromance and data processing. These computers are exceptional computers and are used for large research and scientific purpose. Like NASA is using these computers for launching space shuttles, controlling them and for space exploration purposes. These computers require lot of space for functioning and are externely expensive. The first supercomputer was designed in 1964 namely CDC 6600.

Application of Supter Computers:

1. Weather forecasting: These computers are used to predict and study weather forcasting and to analyze the nature and extent of rainfalls, windstorms.

2. E a r t h q u a k e Studies: Supercomputers are also used for exploring the earthquake phenomenon. They used for resouce exploration like natural gas, petroleum and coal.

3. Communication: These computers are also very useful in enhancing the communication between different devices, different machines and between different individuals.

There are many other uses like weapon simulation and for knowing the impact of nuclear weapons. Some popular supercomputers are:

1. IBM's Sequoia in US

2. Fujitsu's K Computer in Japan

3. PARAM Super computer in India

Mainframe Computers

These computers are also very expensive and are used by government organization, large business firms and for business operations. These computers are kept in big rooms with appropriate coling and other facilites. They can process a large volume of data at a very high speed. Big business banks, educational insittutions and insurance compaies use mainframe computer to store data of their customrs.

Some popular mainframe computers are:

1. Eujitsu's ICL VME

2. Hitachi's Z800

Mini Computers

Mini computers are used by comparatively small business houses. Althrough they are not as powerful as super computers and mainframe computers, but still they are very powerful machines. These are used by big or middle range companies and production houses. These computer uses a single user and a multi user concept also. Some examples of mini computers are:

1. K-202

2. Texas Instrument TI-990

3. SDS-92.

Micro Computers

Desktop computers, laptops, PDAs, tablets and smart phones are all types of microcomputer. These computers are widely used and are fastest growing computers. These are cheapset amongst the all four basic type computers. These computers are general purpose computers and are used for education, entertainment and other office purposes.

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