MICR - What is Magnetic Ink Character Recognition(MICR)?

Magnetic Ink Character Recognition(MICR) is a technique that enables special characters printed in magnetic ink to be read and input rapidly to a computer. When a document that contains this ink needs to be read, it passes through a machine, which magnetizes the ink and then translates the magnetic information into characters.

MICR is used to verify the legitimacy or originality of paper documents, especially checks. MICR is used extensively in banking because magnetic-ink characters are difficult to forge and are therefore ideal for marking and identifying cheques.

   Chapter : Memory & Input/Output Unit
• Computer Fundamental 

Peripheral Device - What is Peripheral Device?

A computer device, such as a CD-ROM drive or printer, which is not part of the essential computer, i.e., the memory and microprocessor. Peripheral devices can be external -- such as a mouse, keyboard, printer, monitor, external Zip drive or scanner -- or internal, such as a CD-ROM drive, CD-R drive or internal modem. Internal peripheral devices are often referred to as integrated peripherals. Linkage between the CPU and the users is provided by Peripheral devices.



Chapter : Memory & Input/Output Unit
• Computer Fundamental 

What is Hard Disk Drive (HDD)?

A Hard Disk Drive (HDD) also hard drive or hard disk is a non-volatile. The harddisk is the primary storage unit of the computer. A harddisk consists of a stack of disk platters that are made up of aluminum alloy of glass coated with a magnetic material; actually, most hard disks have from two to eight platters.

Each side of each platter has a read/write head that floats over the surface of the rapidly spinning disk and picks up (reads) magnetically stored data, or records (writes) data onto the disk. It's just like a tape recorder, except that in a hard disk, the head doesn't touch the disk surface. Instead, the read/write heads float on an extraordinarily thin cushion of air, about the height of a fingerprint. Really. That's why it's important not to jostle your hard disk or kick it while it's doing its work. 

The surface of a disk is divided into imaginary tracks and sectors. Tracks are concentric circles where the data is stored. These tracks are numbered from the outermost ring to the innermost ring, starting from zero. Disk sectors refer to the number of fixed size areas that can be accessed by one of the disk drive’s read/write heads, in one rotation of the disk, without the head having to change its position. An intersection of a track and a disk sector is known as track sector.

Each sector is uniquely assigned a disk address before a disk drive can access a piece of data. In order to make the disk usable, first it must be formatted to create tracks and sectors. The track sectors are grouped into a collection known as cluster. It refers to the basic allocation unit for storage on a disk.

On the hard disk you'll keep the operating system, and copies of all the software applications you use, such as your word processor and your spreadsheet program, plus copies of all the documents or files you create.  The hard drive is sometimes referred to as the "C drive" due to the fact that Microsoft Windows designates the "C" drive letter to the primary partition on the primary hard drive in a computer by default.While this is not a technically correct term to use, it is still common. For example, some computers have multiple drive letters (i.e. C, D, E) representing areas across one or more hard drives.

Some computers don't absolutely need a hard disk for storing things they use floppy disks instead. But a hard disk drive is much, much faster than a floppy disk drive, and it stores much more information. And as software programs and operating systems get more sophisticated, they also take up more disks space-so much disk space that many programs and systems can't even fit on a floppy disk. These days, almost every computer has a hard disk.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

Line Printer - What is Line Printer? Type of Line Printer

Line Printers :- Line Printer can Print One Line at a Time. The line printer is a form of high speed impact printer. They can Print 300 to 3000 Lines per Minute. So that they are very fast. Large Computer system typically use Line Printer. The Line Printers are of two Types.

a)    Drum Printers: - Drum Printer consists of a Drum Which Consists of a Number of Characters; those are Printed on the Drum. And the Number of Characters or Number of Tracks are Divided, after examining the width of the Paper. But there are also Some Character sets Available Means the Number of Characters those are printed on the Paper. For Example 64, and 96 Characters etc.

In this Paper is placed between the Ribbon and the Head or Hammer there are many hammers on the Front of Drum. In this Drum Rotates at a Very High Speed and character is printed by activating the Appropriate Hammer. So always remember that All the Characters are never printed at a Time but they are printed at a very high Speed. And they can print only a Pre Defined Styles because the Drum has a Specific Characters. Those are placed on the Drum. So that they cant print the various Types of Fonts and Color Pictures. And Drum Printers are also noisy because they use Hammering Techniques.

b)   Chain Printers: These are also Line Printers, which Prints one Line at a Time. All the Characters are printed on the Chain and the Set of Characters are placed on the Chain. There are 48 and 64 and 96 Characters set Printers are Available. There are also Some Hammers, those are Placed in Front of the Chain, and Paper is Placed between the Hammer and the Inked Ribbon. The Total Number of Hammers will be Equals to the Total Number of Print Positions.

                   In this Chain Rotates at a Very High Speed and Character is printed by activating the Appropriate Hammer of the Character. Chain Printers can also print some Pre Defined characters and we can’t Display the High Quality of Fonts and Font Styles. They are also Impact Printers and Also Noisy because they Prints the Characters by Hammering Action. And these Printers can print the 400 to 3000 Lines Per Minute.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

Primary Storage - What is Primary storage ?

Primary Storage, also known as main storage or memory, is the main area in a computer in which data is stored for quick access by the computer's processor. Information must be transferred to primary storage. On today's smaller computers, especially personal computers and workstations, the term random access memory (RAM) - or just memory - is used instead of primary, main storage, core memory, or immediate access storage, internal storage, and the hard disk, diskette, CD, and DVD collectively describe secondary storage or auxiliary storage.

It allows very fast access to data. It is relatively move expensive. A CPU has three element or parts primary storage, arithmetic logic unit (ALU), and control unit. Primary storage is fast and expensive as compared to secondary storage.

The terms main storage and auxiliary storage originated in the days of the mainframe computer to distinguish the more immediately accessible data storage from storage that required input/output operations.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

What is Access Method? Explain Different type of Access Methods

In computing, an access method is a program or a hardware mechanism that moves data between the computer and an outlying device such as a hard disk (or other form of storage) or a display terminal.

The term is sometimes used to refer to the mechanics of placing or locating specific data at a particular place on a storage medium and then writing the data or reading it. It is also used to describe the way that data is located within a larger unit of data such as a data set or file.

 There are two type of access method random access and sequential access.

To go from point A to point Z in a sequential-access system, you must pass through all intervening points. In a random-access system, you can jump directly to point Z.Disks are random access media, whereas tapes are sequential access media.

The terms random access and sequential access are often used to describe data files. A random-access data file enables you to reador write information anywhere in the file. In a sequential-access file, you can only read and write information sequentially, starting from the beginning of the file.

Both types of files have advantages and disadvantages. If you are always accessing information in the same order, a sequential-access file is faster. If you tend to access information randomly, random access is better.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

SemiConductor Memory - What is SemiConductor Memory ?

A device for storing digital information that is fabricated by using integrated circuit technology. Also known as integrated-circuit memory; large-scale integrated memory; memory chip; semiconductor storage; transistor memory.

Semiconductor memory

Semiconductor memory technology is an essential element of today's electronics. Normally based around semiconductor technology, memory is used in any equipment that uses a processor of one form or another.

With the rapid growth in the requirement for semiconductor memories there have been a number of technologies and types of memory that have emerged. Names such as ROM, RAM, EPROM, EEPROM, Flash memory, DRAM, SRAM, SDRAM, and the very new MRAM can now be seen in the electronics literature. Each one has its own advantages and area in which it may be used.

Types of semiconductor memory

Electronic semiconductor memory technology can be split into two main types or categories, according to the way in which the memory operates:

RAM - Random Access Memory:

Random Access Memory (RAM)is the best known form of computer memory. The Read and write (R/W) memory of a computer is called RAM. The User can write information to it and read information from it.

The RAM is a volatile memory, it means information written to it can be accessed as long as power is on. As soon as the power is off, it can not be accessed. so this mean RAM computer memory essentially empty.RAM holds data and processing instructions temporarily until the CPU needs it. Scratchpad storage in memory space is used for the temporary storage of data.

ROM - Read Only Memory:

Read only memory (ROM) is an example of nonvolatile memory.  ROM is a class of storage medium used in computers and other electronic devices. Read Only Memory (ROM), also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. The instructions for starting the computer are housed on Read only memory chip.

Semiconductor Memory Technologies

There is a large variety of types of ROM and RAM that are available. These arise from the variety of applications and also the number of technologies available. This means that there is a large number of abbreviations or acronyms and categories for memories ranging from Flash to MRAM, PROM to EEPROM, and many more:

PROM:     This stands for Programmable Read Only Memory. It is a semiconductor memory which can only have data written to it once - the data written to it is permanent. These memories are bought in a blank format and they are programmed using a special PROM programmer. Typically a PROM will consist of an array of fuseable links some of which are "blown" during the programming process to provide the required data pattern.

The PROM stores its data as a charge on a capacitor. There is a charge storage capacitor for each cell and this can be read repeatedly as required. However it is found that after many years the charge may leak away and the data may be lost. Nevertheless, this type of semiconductor memory used to be widely used in applications where a form of ROM was required, but where the data needed to be changed periodically, as in a development environment, or where quantities were low.

EPROM:     This is an Erasable Programmable Read Only Memory. This form of semiconductor memory can be programmed and then erased at a later time. This is normally achieved by exposing the silicon to ultraviolet light. To enable this to happen there is a circular window in the package of the EPROM to enable the light to reach the silicon of the chip. When the PROM is in use, this window is normally covered by a label, especially when the data may need to be preserved for an extended period.

EEPROM:     This is an Electrically Erasable Programmable Read Only Memory. Data can be written to it and it can be erased using an electrical voltage. This is typically applied to an erase pin on the chip. Like other types of PROM, EEPROM retains the contents of the memory even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM.

EEPROM memory cells are made from floating-gate MOSFETS (known as FGMOS)

Flash memory:     Flash memory may be considered as a development of EEPROM technology. Data can be written to it and it can be erased, although only in blocks, but data can be read on an individual cell basis. To erase and re-programme areas of the chip, programming voltages at levels that are available within electronic equipment are used. It is also non-volatile, and this makes it particularly useful. As a result Flash memory is widely used in many applications including memory cards for digital cameras, mobile phones, computer memory sticks and many other applications.

Flash memory stores data in an array of memory cells. The memory cells are made from floating-gate MOSFETS (known as FGMOS). These FG MOSFETs (or FGMOS in short) have the ability to store an electrical charge for extended periods of time (2 to 10 years) even without a connecting to a power supply.

DRAM:     Dynamic RAM is a form of random access memory. DRAM uses a capacitor to store each bit of data, and the level of charge on each capacitor determines whether that bit is a logical 1 or 0. However these capacitors do not hold their charge indefinitely, and therefore the data needs to be refreshed periodically. As a result of this dynamic refreshing it gains its name of being a dynamic RAM. DRAM is the form of semiconductor memory that is often used in equipment including personal computers and workstations where it forms the main RAM for the computer.

Disadvantage: Need to refresh the capacitor charge every once in two milliseconds

SRAM:     Static Random Access Memory. This form of semiconductor memory gains its name from the fact that, unlike DRAM, the data does not need to be refreshed dynamically. It is able to support faster read and write times than DRAM (typically 10 ns against 60 ns for DRAM), and in addition its cycle time is much shorter because it does not need to pause between accesses. However it consumes more power, is less dense and more expensive than DRAM. As a result of this it is normally used for caches, while DRAM is used as the main semiconductor memory technology.

SDRAM:     Synchronous DRAM. This form of semiconductor memory can run at faster speeds than conventional DRAM. It is synchronised to the clock of the processor and is capable of keeping two sets of memory addresses open simultaneously. By transferring data alternately from one set of addresses, and then the other, SDRAM cuts down on the delays associated with non-synchronous RAM, which must close one address bank before opening the next.

MRAM:     This is Magneto-resistive RAM, or Magnetic RAM. It is a non-volatile RAM memory technology that uses magnetic charges to store data instead of electric charges. Unlike technologies including DRAM, which require a constant flow of electricity to maintain the integrity of the data, MRAM retains data even when the power is removed. An additional advantage is that it only requires low power for active operation. As a result this technology could become a major player in the electronics industry now that production processes have been developed to enable it to be produced.

History of Computer Memory

* In 1932 Gustav Tauschek invents drum memory in Austria.

* 1936 Konrad Zuse applies for a patent for his mechanical memory to be used   in   his computer.
  This computer memory is based on sliding metal parts.

* 1939 Helmut Schreyer invents a prototype memory using neon lamps.

* 1942 The Atanasoff-Berry Computer has 60 50-bit words of memory in the form of capacitors mounted on two revolving drums.     For secondary memory it uses punch cards.

* 1947 Frederick Viehe of Los Angeles, applies for a patent for an invention that uses magnetic core memory. Magnetic drum   memory is independently invented by several people.

* 1949 Jay Forrester conceives the idea of magnetic core memory as it is to become commonly used, with a grid of wires used   to address the cores. The first practical form manifests in 1952-53 and renders obsolete previous types of computer memory.

* 1950 Ferranti Ltd. completes the first commercial computer with 256 40-bit words of main memory and 16K words of drum   memory. Only eight were sold.

* 1951 Jay Forrester files a patent for matrix core memory.

* 1952 The EDVAC computer is completed with 1024 44-bit words of ultrasonic memory. A core memory module is added to the     ENIAC computer.

* 1955 An Wang was issued U.S. patent #2,708,722 with 34 claims for magnetic memory core.

* 1966 Hewlett-Packard releases their HP2116A real-time computer with 8K of memory. The newly formed Intel starts sell a   semiconductor chip with 2,000 bits of memory.

* 1968 USPTO grants patent 3,387,286 to IBM's Robert Dennard for a one-transistor DRAM cell. DRAM stands for Dynamic RAM   (Random Access Memory) or Dynamic Random Access Memory. DRAM will become the standard memory chip for personal computers   replacing magnetic core memory.

* 1969 Intel begin as chip designers and produce a 1 KB RAM chip, the largest memory chip todate. Intel soon switch to being   notable designers of computer microprocessors.

* 1970 Intel releases the 1103 chip, the first generally available DRAM memory chip.

* 1971 Intel releases the 1101 chip, a 256-bit programmable memory, and the 1701 chip, a 256-byte erasable read-only memory   (EROM).

* 1974 Intel receives a U.S. patent for a "memory system for a multichip digital computer".

* 1975 Personal consumer computer Altair released, it uses Intel's 8-bit 8080 processor and includes 1 KB of memory. Later in   the same year, Bob Marsh manufacturers the first Processor Technology's 4 kB memory boards for the Altair.

* 1984 Apple Computers releases the Macintosh personal compututer. It is the first computer that came with 128KB of memory.   The one-megabyte memory chip is developed.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

Read Only Memory. What are the types of ROM

Read Only Memory (ROM) is an example of nonvolatile memory.  ROM is a class of storage medium used in computers and other electronic devices. Read Only Memory (ROM), also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. The instructions for starting the computer are housed on Read only memory chip.

ROM chips are used not only in computers, but in most other electronic items as well. Because data is fully incorporated at the ROM chip's manufacture, data stored can neither be erased nor replaced. This means permanent and secure data storage. However, if a mistake is made in manufacture, a ROM chip becomes unusable. The most expensive stage of ROM manufacture, therefore, is creating the template.

If a template is readily available, duplicating the ROM chip is very easy and affordable. A ROM chip is also non volatile so data stored in it is not lost when power is turned off. ROM is a  semiconductor memory that is capable of operating at electronics speed.

                                                             ROM Types : 

 PROM : Short for programmable read-only memory, a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike RAM, PROMs retain their contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.

EPROM : Acronym for erasable programmable read-only memory, and pronounced ee-prom, EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner.

EEPROM : Short form of electrically erasable programmable read-only memory. EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

How can you classify Storage Devices? What are its different types elaborate?

Storage Device is a device for recording (storing) information (data). Recording can be done using virtually any form of energy.storage device is a hardware device capable of storing information. There are two storage devices used in computers; a primary storage device such as computer RAM and a secondary storage device such as a computer hard disk drive.

Primary Storage: - Primary storage is a storage location that holds memory for short periods of times while the computer is on. For example, computer RAM (random-access memory) and cache are both examples of a primary storage device. This type of storage is the fastest type of memory in your computer and is used to store data while it’s being used. For example, when you open a program data is moved from the secondary storage into the primary storage. It is also known as internal memory and main memory.

 Secondary Storage: - Secondary storage is a storage medium that holds information until it is deleted or overwritten regardless if the computer has power. For example, a floppy disk drive and hard disk drive are both good examples of secondary storage devices. As can be seen by the below picture there are three different types of storage on a computer, although primary storage is accessed much faster than secondary storage because of the price and size limitations secondary storage is used with today’s computers to store all your programs and your personal data.

It is also known as external memory and auxiliary storage. Off-line storage in Fig  could be considered secondary storage, we’ve separated these into their own category because these types of media can be easily removed from the computer and stored elsewhere.

Floppy Disk : It’s a circular disk coated with magnetic oxide and enclosed within square plastic cover (Jacket). It’s available in different size, but the most commonly used floppy is 3½. Data up to 1.44 MB can be stored in it. Data is written as tiny magnetic spots on the dish surface creating new data or a disk surface eraser data previously stored at that location. Floppies are available in 2 sizes, 3.5 inch & 5.25 inch. The 3.5 inch size floppy is mostly used. The 5.25 inch floppy is kept in a flexible cover & it’s not safe. It can store about 1.2 MB data.

Hard Disk : Hard disks are made of aluminum or other metal alloys which are coated on both sides with magnetic material. Unlike floppy disks, hark disks are not removable from the computer. To remain the storing capacity several disks are packed together & mounted on a common drive to form a disk pack. A disk is also called a platter.

Magnetic Tape: Magnetic Tape can be used to perform both functions -input and output. Magnetic Tape is a secondary storage media. Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time. In PC also you can use tapes in the form of cassettes. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic film-type and 500 meter to 1200 meter long which is coated with magnetic material. The deck is connected to the central processor and information is fed into or read from the tape through the processor. It similar to cassette tape recorder.

Advantages of Magnetic Tape:

• Compact: A 10-inch diameter reel of tape is 2400 feet long and is able to hold 800, 1600 or 6250 characters in each inch of its length. The maximum capacity of such tape is 180 million characters. Thus data are stored much more compactly on tape.

• Economical: The cost of storing characters is very less as compared to other storage devices.

• Fast: Copying of data is easier and fast.

• Long term Storage and Re-usability: Magnetic tapes can be used for long term storage and a tape can be used repeatedly with out loss of data. 

Magnetic Disk: You might have seen the gramophone record, which is circular like a disk and coated with magnetic material. Magnetic disks used in computer are made on the same principle. It rotates with very high speed inside the computer drive. Data is stored on both the surface of the disk. Magnetic disks are most popular for direct access storage device.

Each disk consists of a number of invisible concentric circles called tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot represents one bit and its absence represents zero bit. The information stored in a disk can be read many times without affecting the stored data. So the reading operation is non-destructive. But if you want to write a new data, then the existing data is erased from the disk and new data is recorded.

Optical Disk : Information is written to or read from an optical disk or tape using laser beam. Optical disks are not suitable memory storage units because their access time is more than that of hard disks. Their advantage is that they have very high storage capacity.

Types of optical memory are: CD –ROM, CD-R, CD-RW, DVD-ROM, DVD-R and DVD-RW. Information on a CD-ROM is written at the time of manufacture. CD-R/W of 700 MB are available. A DVD-ROM is similar to CD-ROM. It uses shorter wave length of laser beam and hence, stores more data than CD-ROM.

With every new application and software there is greater demand for memory capacity. It is the necessity to store large volume of data that has led to the development of optical disk storage medium. Optical disks can be divided into the following categories:

1. Compact Disk/ Read Only Memory (CD-ROM): CD-ROM disks are made of reflective metals. CD-ROM is written during the process of manufacturing by high power laser beam. Here the storage density is very high, storage cost is very low and access time is relatively fast. Each disk is approximately 4 1/2 inches in diameter and can hold over 600 MB of data. As the CD-ROM can be read only we cannot write or make changes into the data contained in it.

2. Write Once Read Many (WORM): The inconvenience that we can not write any thing in to a CD-ROM is avoided in WORM. A WORM allows the user to write data permanently on to the disk. Once the data is written it can never be erased without physically damaging the disk. Here data can be recorded from keyboard, video scanner, OCR equipment and other devices. The advantage of WORM is that it can store vast amount of data amounting to gigabytes (109 bytes). Any document in a WORM can be accessed very fast, say less than 30 seconds.

3. Erasable Optical Disk: These are optical disks where data can be written, erased and re-written. This also applies a laser beam to write and re-write the data. These disks may be used as alternatives to traditional disks. Erasable optical disks are based on a technology known as magnetic optical (MO). To write a data bit on to the erasable optical disk the MO drive's laser beam heats a tiny, precisely defined point on the disk's surface and magnetizes it.

Chapter : Memory & Input/Output Unit
• Computer Fundamental  

Interrupt - What is Interrupt? Types of Interrupts

                When a Process is executed by the CPU and when a user Request for another Process then this will create disturbance for the Running Process. This is also called as the Interrupt. Interrupts can be generated by User, Some Error Conditions and also by Software’s and the hardware’s. But CPU will handle all the Interrupts very carefully because when Interrupts are generated then the CPU must handle all the Interrupts Very carefully means the CPU will also Provides Response to the Various Interrupts those are generated. So that When an interrupt has Occurred then the CPU will handle by using the Fetch, decode and Execute Operations.

                                                         Types of Interrupts

Generally there are three types o Interrupts those are Occurred For Example

1)   Internal Interrupt

2)   Software Interrupt.

3)   External Interrupt.

The External Interrupt occurs when any Input and Output Device request for any Operation and the CPU will Execute that instructions first For Example When a Program is executed and when we move the Mouse on the Screen then the CPU will handle this External interrupt first and after that he will resume with his Operation.

The Internal Interrupts are those which are occurred due to Some Problem in the Execution For Example When a user performing any Operation which contains any Error and which contains any type of Error. So that Internal Interrupts are those which are occurred by the Some Operations or by Some Instructions and the Operations those are not Possible but a user is trying for that Operation. And The Software Interrupts are those which are made some call to the System for Example while we are Processing Some Instructions and when we wants to Execute one more Application Programs.

Storage Devices

                   As we know that the Main Memory Stores the data in a Temporary Manner means all the data will be loss when the Power switched off. And all the data will be loss when the power goes switched off.

So that we uses the Secondary Storage devices those are used for Storing the data in a Permanent Manner means all the Data will remain Stored whether the Power is Switched on or Switched off means the Power Will never effect on the System. For storing the data in a Permanent Manner we uses the Magnetic Storage Devices. There are also Some Advantages of Secondary Storage Devices.

1) Non-Volatile Storage Devices: The Non-Volatile Storage Devices are Non-Volatile in the nature means them never loss their data when the Power goes switched off. So that data which is Stored into the Non-Volatile Storage Devices will never be Loosed When the Power Switched off.

2) Mass Storage: The Capacity of these Devices is very high means we can Store the Huge Amount of data into the Secondary Storage Devices. We can Store data into the Secondary Storage Devices in the form of Giga Bytes and Tera Bytes.

3) Cost Effective: The Cost of Secondary Storage Devices is very lower in compare to the Main Memory So that they are also called as the more cost effective and they are very small and couldn’t easily damage. And the data can’t be easily loss from these Disks.

4) Reusability: As Memory Contains the Data in the Temporary as well as Permanent Manner. But the Secondary Storage Devices are always Reusable means they can be erased and stored any Time. Means we can add or Remove the Contents from these Disks when we Requires.

There are Many Types of Storage Devices those are based on the Sequential and Random Access Means the data which is Stored into the Secondary Storage devices can be Read either from the First Location which is also known as the Sequential Access or Sequential Manner and the Data can be Read from these Disks and also from any Locations. So if any Disk provides this Utility then this is called as the Direct Access Mechanism. There are Many Storage Devices those are either based on the SASD or Some are DASD.

Various types of Secondary Storage Devices are as Followings: -

1) Magnetic Tapes: The Magnetic Tapes is the Type of Secondary Storage Device and this Device is used for taking back up of data and this Tape contains some magnetic fields and the Magnetic Tapes are used Accessing the data into the Sequential Form and the Tape Also Contains a Ribbon which is coated on the Single Side of the Tape and also contains a head which reads the data which is Recorded on to the Tape. And when we are reading the information from the disk then we can also read backward information means we can also back the Tape for Reading the Previous information. And For inserting the Tape into the System we also Requires Some Tape Drives Which Contains Tape and which is Responsible for Reading the contents from the Tapes.

They can Store huge Amount of data into the Tape Drive , But the Main Limitation of the Tape Drive is that we cant Access the Data from the Disks directly means if we wants to 100th Record from the Tape then we must have to move all the Previous i.e. 99th Records first. And the Tapes are also easily damaged due to the Human Errors.

2) Magnetic Disks : - This is also called as the hard disk and this is made from the thin metal platter which is coated on the both sides of the magnetic Disks. And the there are Many Plates or Platters into a single Hard Disk and all the Plates are Made from the Magnetic Materials and all the Disks are Rotate from the 700 to 3600 rpm means Rotation per Minute and the Hard Disk also Contains a head which is used for both Reading and Writing the Data from the Hard Disks.

The Plate of Disk is Divided into the Tracks and sectors and the collection of Tracks makes a Cylinder means all the Tracks of the Disk which a Consecutive Areas makes a Cylinder.

The Disk is first divided into the Number of Tracks and the Tracks are further divided into the sectors and the Number of Tracks Makes a Cylinder. All the data is Stored into the disk by using Some Sectors and each sectors belongs to a Tracks. The Data is accessed from the Disk by using the heads, all the heads have Some Arm those are used for Reading the Data from the Particular Tracks and sector. When the Disk Rotates very high Speed then the Head also Moves, For Reading the data from the Disk the ARM touches with the Particular Track and read the data from that Location.

For Locating a Particular data from the Disk the head Moves Around the Disk very Fastly and data which a user wants to Access must have an Address So that Arm of the head just use that Address Means the Number of Cylinder, Number of Track and Number of Sectors from which user wants to read the data. With the Help of these Read and Write heads we can also Read the Data from the Disk and we can also Stores some data onto the Disk. Some Time Considerations are also used when we are accessing or storing the data onto the hard disk.

1)  Seek Time: - The Total Time which is Taken to Move on the Desired track is known as the seek Time. And time is always measured by using the Milliseconds.

2)  Latency Time. : The time required to Bring the Particular Track to the Desired Location Means the Total Time to bring the Correct the Sector for Reading or for the read and Write head. This is also called as the Average Time.

3)  Data Transfer Time: The Total Time which is required for Reading and Writing the data into the Disk is known as the Data transfer Time.

When we are Taking About the Magnetic Tapes then we can say that the Storage Capacity of the disk is Measure in the Form of Mega Bytes and when are talking about the Hard Disk then the Measurement will be in the Form of Giga Bytes. Means the Capacity of t the Hard Disk will be Read by using the Giga Bytes. The Magnetic Tapes are Sequential Access Device and the Hard Disk is the Direct Access Device means the data of this Disk will be Read from Any Location and the Data can be Read from the Disk by using the Read Write Heads. But hard Disks are Costlier than the Simple Magnetic Tapes. But the capacity of the Hard Disk is very high in compare to the Tapes.

3) Floppy Diskette: Floppy disk is a kind of storage device that can be used to  carried around? The Floppy Disk is also a Secondary Storage device which is used for storing the data in a Permanent Manner. The floppy is made up of Rigid Mylar Plastic and also contains a Magnetic black disk inside the Plastic Cover. The Floppy Disk also Stores all the Data into the Form of Tracks and Sectors and the floppy Disk provides both Reading and Writing the data into the Disk. The Floppy Disk is also called as Reusable Disk means the Floppy Disk Provides us the Facility to Read and Writes the Data into disk as and When Necessary and Also Many Times. We can Read and Write the data from the Disk.

The Main Advantage of the Floppy Disk is that the Data can be Stored many Times but the Main Limitation of the floppy Disk is that floppy Disk have a Small capacity and the Floppy Disk also doesn’t have Reliability means the Data Stored into the Disk may not be used for Long Time because the floppy Disk is very Sensitive Thing when we Move the Head of the Disk Again and Again then the floppy disk gets Damaged. So that we can say that Floppy Disk is not a Reliable thing. And I the Other side the Cost of floppy Disk is also high means with the Comparison of the Other Storage Media’s Floppy Disk have some more cost.

But the Main Advantage of the Floppy Disk is that floppy Disk is used for Moving the data from one Computer to Another With the Advent of the Floppy Disk we can Store the Data Into the Floppy Disk and after that we can Easily Remove that Disk from the System and Also Put the Disk into the Another System for Taking the Data.

But we can not Start or Run the System without the Hard Disk So that floppy Disk is used to Transfer the Files from one System into the. There are Two Types of floppy Disk Available first is the 3.5 and second is the 5.2. But for inserting the Floppy Disk into the System we must have to use the Floppy Disk Drive in the System.

For Reading the data from the Disk there are also Some Read and Write heads those are too used. And the Head will touch the Surface of the floppy Disk So that this will lead to the Damage of the Disk So Quickly because when the Head Directly Touch the Surface of the Disk, then this will lead to the Scratches on the Disk and also cause Damage of the Disk. And the Drive can take only one Disk Means we can insert only one Floppy Disk at a Time into the Floppy Drive. The capacity of the floppy Disk is 1.44 MB. So that we can Floppy Disks as rare as Possible.

Floppy Disk Contains a Notch which Specify Whether the data will be Read or Write Means to Say if we wants to Protect our data then we can set the Notch of the Floppy Disk as a Read Only.

4) Optical Disks: The Optical Disks are also called as the CD-ROM’s means Compact Disk Read Only Memory which is also used for Storing the data into the Disk and this is called as the Optical Disk because the CD-ROM ‘s are made up of the Golden or Aluminum Material and the data is Stored on the Disk in the Form of the Tracks and Sectors. The Whole Disk is Divided into the Number of Tracks and the Single Track is Divided into the Number of Sectors and the Data is Stored into the Sectors and the Disk is Divided into the Sectors as the first Track Contains the Sectors in the huge Size and the Other Tracks contains the Sectors in a Small Manner. So that as the Disk grows the Disk is Divided into the Small Number of Tracks and the Sectors.

CD-ROM Contains the data Which is truly Read able means we cant edit the contents of the CD-ROM Means once Data has been Written into the CD , we can be able to Change the Contents of the Disk and the Data which is Stored on the Disk can be Any Time Read by the user. The CD-ROM provides us the Large Capacity in compare to the Floppy Disks and the CDROM can Store the Data from 650 MB to 800 MB means the data can be Store up to this Space.

There are Many Disks that cant be Erased once Written So they are also called as the WORM Disks Means the Write Once and Read Many Mane a user can just Write the data only one Time and then after that he can use that Disk Many Times but a user cant Edit or Change those Contents after they are Written into the File. So that these Disks are not Reusable. So that  these Types of Optical Disks are also called as the CD-ROM and also Some Times they are known as the CD-R Means the Read Only Disks because the data which is Written into these Types of Disks is never to be Erased.

Now these Days there are also Some CDs Available those are also called as the CD-RW or Read Writable Disks. As the Name Suggest these Disks Provides the feature to the user to Read and Write the Contents from the Disk as they feel Necessary So that the CD-RW are now Most Popular because a user can any Time Remove the Contents from the Disk and also he can store the new Contents into the Disk.

The CD-R and CD-RW both have Same Capacity and both these can be used for Transferring the Files from one System to another but the Main difference is that the cost. The CD-RW has Some More Cost in compare to the Simple CD or in Compare to the CD-R.

Winchester Disk

Another term for hard disk drive. The term Winchester comes from an early type of disk drive developed by IBM that had 30MB of fixed storage and 30MB of removable storage; so its inventors called it a Winchester in honor of its 30/30 rifle. Although modern disk drives are faster and hold more data, the basic technology is the same, so Winchester has become synonymous with hard.

Magnetic Drum

A direct-access, or random-access, storage device. A magnetic drum, also referred to as drum, is a metal cylinder coated with magnetic iron-oxide material on which data and programs can be stored. Magnetic drums were once used as a primary storage device but have since been implemented as auxiliary storage devices.

The tracks on a magnetic drum are assigned to channels located around the circumference of the drum, forming adjacent circular bands that wind around the drum. A single drum can have up to 200 tracks. As the drum rotates at a speed of up to 3,000 rpm, the device's read/write heads deposit magnetized spots on the drum during the write operation and sense these spots during a read operation. This action is similar to that of a magnetic tape or disk drive.

Unlike some disk packs, the magnetic drum cannot be physically removed. The drum is permanently mounted in the device. Magnetic drums are able to retrieve data at a quicker rate than tape or disk devices but are not able to store as much data as either of them.

Chapter : Memory & Input/Output Unit
• Computer Fundamental 

What is CISC and RISC? Explain RISC in detail

                           

                       CISC (Complex Instruction Set Computer) : It was developed by Intel. CISC is a type of design for the computers. CISC based computer will have shorter programs which are made up of symbolic machine language.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                     A Complex Instruction Set Computer (CISC) supplies a large number of complex instructions at the assembly language level. During the early years, memory was slow and expensive and the programming was done in assembly language. Since memory was slow and instructions could by retrieved up to 10 times faster from a local ROM than from main memory, programmers tried to put as many instructions as possible in a microcode. 

RISC (Reduced Instruction Set Computer) : RISC is a type of microprocessor that has a relatively limited number of instructions. It is designed to perform a smaller number of types of computer instructions so that it can operate at a higher speed (perform more million instructions per second, or millions of instructions per second). Earlier, computers used only 20% of the instructions. Making the other 80% unnecessary. One advantage of reduced instruction set computers is that they can execute their instructions very fast because the instructions are so simple.

RISC chips require fewer transistors, which makes them cheaper to design and produce. In a RISC machine, the instruction set contains simple, basic instructions, from which more complex instructions can be composed. Each instruction is of the same length, so that it may be fetched in a single operation. Most instructions complete in one machine cycle, which allows the processor to handle several instructions at the same time. This pipelining is a key technique used to speed up RISC machines.

  

Advantages :

i) Speed : Since a simplified instruction set allows for a pipelined, superscalar design RISC processors often achieve 2 to 4 times the performance of CISC processor using comparable semiconductor technology and the same clock rates.

ii) Simpler Hardware : Because the instruction set of a RISC processor is so simple, it uses up much less chip space; extra functions, such as memory management units or floating point arithmetic units, can also be placed on the same chip. Smaller chips allow a semiconductor manufacturer to place more parts on a single silicon wafer, which can lower the per-chip cost dramatically.

iii) Shorter Design Cycle : Since RISC processors are simpler than corresponding CISC processors, they can be designed more quickly, and can take advantage of other technological developments sooner than corresponding CISC designs, leading to greater leaps in performance between generations.