හි සියලුම ප්‍රකාශන Malaka Dilshan . දෙහිවල-ගල්කිස්ස , ශ්‍රී ලංකාව

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Computer Storage devices

Definition of computer storage devices

A storage device is some kind of hardware, which can store data or information temporarily or permanently. It is also known as storage, storage devices or storage media. It has the ability of hold and port data files. Storage devices can use internally or externally to any comparable computing system. Storage device is a core component that available in several structures and various form factors. A computer device includes different storage devices RAM, ROM, cache, hard disk, USB drives and that all can be divided into two parts primary and secondary.

The usage of storage devices

A computer can be considered as a dumb terminal without a storage device. It won’t be able to store data or any type of information or settings it has no any data storage facilities. And also, a storage device is needed to store control instructions, program files of application software. Such tasks like display setting sound control. Furthermore, like USB flash drive devices have ability to move information to any other computer.

Types of storage

· Primary storage

o Primary storage allows computer to store data for access vary fast, manipulate immediately and keep doing and keep the way of what is being processed. This includes main memory (RAM and ROM) and internal processor memories (cache memory). As soon as the system leads to a power cut or a crash, the data also get lost.

· Secondary storage

o The secondary storage can be considered as the components which are designed to store data permanently. They have very large storage capacity compared to the primary storage. The hard disk, USD drive storage, optical drive are some examples. It differs from primary storage in that it is not directly accessible by the central processing unit.

· Tertiary storage

o It is a very large storage that is external from the computer system. It has the slowest speed. Tertiary storage involves a robotic mechanism which will mount and dismount removable mass storage media into a storage device according to the system’s demand. Tertiary storage is generally used for data backup. Optical storage (CD, DVD), tape storage are some examples of tertiary storage.

· Offline storage

o Floppy disks, compact disks and USB drivers are some common examples of offline storage which must be physically inserted into a computer when users want to access or edit data. Offline storage is can be considered as any storage that is not online, live or connected to the computer. It is portable and can be used on several computer system. Offline storage can be internal or external storage that can easily remove from the computer. Offline storage is also known as removable storage.

Types of computer storage devices

· Magnetic storage devices

o Magnetic storage devices are a form of non- volatile memory and stores data on a magnetized medium. This device uses different pattern of magnetization in a magnetized material to store data. The data is accessed by using one or more read and write heads.

· Optical storage devices

o Optical devices can be considered as an electronic data storage which read and write data by using optical technology. Light is used to aid the device in riding the data that stored. Blu-ray disc, compact disc (CD), digital versatile disc (DVD).

· Flash Memory devices

o Flash memory is portable as well as cheaper. Because of more reliable and effective solution, most of magnetic and optical devices have replaced by flash memory devices.

· Online Cloud storage devices

o It can be considered as “the storage of data online in the cloud”. cloud storage is capable of store any type of data in digital form. The data that stored in, can access from anywhere, anytime. Some cloud storage provides providers such as, Google drive, Dropbox, one drive, I Cloud provide free service for limited storage. Users have to pay for the storage beyond the limit.

Most used storage devices

Floppy Diskette

· Floppy Diskettes are portable hardware components that can store data up to 1.44 MB. Floppy disks are slower to access than hard disks and have less storage capacity. Early version of floppy disk came two sizes, 5.25 inches (360 kB) and 3.5 inches (1.44 MB). As the technology advanced, floppy disk become smaller and came in three sizes, 8 inches, 5.5 inches and 3.5 inches.


Hard drive

·

Hard disk drive is a non- volatile computer storage device that used to store data permanently. Internal hard drive is directly connected to the disk controller of the motherboard. HDD is known as secondary storage device.

Zip diskette

· Zip diskette is an advanced version of the floppy disk. It functions like a 1.44” floppy drive. It was very popular in 1990s and can be stores data that was not possible with ordinary floppy disk. Zip diskette is developed by lomega.


CD

· CD stands for compact disk. Cd are circular disks that use optical rays(laser) to read and write data. CDs are very cheap and easy to use. It is capable of contain a 700 MB storage. There are three types of CDs.

1. CD-ROM (compact disk - read only memory)

2. CD-R (compact disk - recordable)

3. CD-RW (compact disk - rewritable)


DVD

·

DVD stands for digital video display. It is capable of hold 15 times more data held by CD. They are usually used to store high quality multimedia files that need more storage capacity. They also came in DVD- ROM, DVD-R, DVD-RW. Widely used for store movies and to deliver software files.

Blu ray disk

· Blu ray disk is an optical storage media that can store high definition multimedia files. It uses shorter wave length laser rays than CD or DVD to read and write data, that enable to focus more tightly on the disk surface. It can hold up to 128 GB data.


USB Flash Drive

· USB flash drives are very essential for move files from one device to another very easily. It is a small and ultra- portable storage device. Flash drives are also referred as the pen drives or thumb drives. USB can contain up to 2 TB storage. The first flash drive introduced to the market in 2000 with a storage of 8 MB.


SD card

· Secure digital card had shorten as SD. It is most often used in smart phones and digital cameras. It can be removed from the device and connected with the computer by USB port via a card reader. It is designed to offer large memory with a small size. Standard SD cards, mini SD cards and micro SD cards are available with various speeds, sizes and capacities.


Solid- state drive

· SSD id the short form of solid- state drive. SSD is a non- volatile storage medium that differs from the hard drive. It doesn’t have moving parts. Faster access, soundless operation, less power consumption are some advantages of SSD. Because of efficient features, it became a replacement for a standard hard drive in PCs.


RAM

· RAM is the short term of Random-Access Memory. It is a volatile memory, that means it doesn’t store data or instructions permanently. RAM is the one of the faster types of main memory can be accessed directly by the CPU. It is used by the CPU to read and write memory until computer is turned off. When the computer is turned off, the data stored in the RAM will be lost. There are two types of RAM.

1. SRAM (Static Random- Access Memory)

2. DRAM (Dynamic Random- Access Memory)


ROM

· ROM is the short term of Read Only Memory. It is non- volatile memory. It means ROM doesn’t lost the data that written on it when the computer shut down or at a power cut. This permanent memory contains important data and instructions that need to perform tasks in the computer like boot process. There are five types of RAM.

1. MROM (Masked Read Only Memory)

2. PROM (Programmable Read Only Memory)

3. EPROM (Erasable and Programmable Read Only Memory)

4. EEPROM (Electrically Erasable and Programmable Read Only Memory)

5. Flash ROM

Cache Memory

· Cache memory is a small sized chip-based memory that lies between the CPU and the main memory. It is a high-speed memory. Also, faster than the RAM. The CPU can access it more quickly. Cache memory makes sure that the data which CPU used frequently, is available for CPU whenever the CPU needs this data. L1(onboard/internal/primary cache), L2(external or secondary cache), L3 are the types of cache memory.

Characteristics of computer storage devices

· Volatility

Two types of volatility.

o Volatile memory

o Non-volatile memory

Volatile

Non-Volatile

· Requires constant power to maintain the stored information.

· Data remains stored even if it is powered off.

· Stored temporarily.

· Stored permanently.

· Faster than non- volatile.

· Slower than volatile.

· Process can read and write.

· Process can only read.

· Has less storage capacity.

· Has more storage capacity.

· CPU has direct access of data.

· CPU has no direct access of data.

· Ex: RAM

· Ex: ROM

· Accessibility

Two types of accessibility.

o Random Access

o Sequential Access

Random Access- This method can jump any specified location randomly. This characteristic is well suitable for primary and secondary storage. This type can access any location approximately same time.

Sequential Access- In sequential access, memory is accessed in a specific serial order. The access time depends on the upon which piece of information was last accessed.

· Mutability

A computer without some amount of read or write storage for primary storage purposes would be useless for many tasks. Mutability allows information to be overwritten at any time. There are three types of mutability:

o Read/write storage or mutable storage

o Read only storage

o Slow write, fast read storage

Read or write storage or mutable storage - Allows information to be overwritten at any time. Modern computers typically use read/write storage also for secondary storage.

Read Only Storage- Retains the information stored at the time of manufacture, and write once storage (WORM) allows the information to be written only once at some point after manufacture. These are called immutable storage that used for tertiary and off-line storage.

Slow write, fast read storage- Read and write storage which allows information to be overwritten multiple times, but with the write operation being much slower than the read operation.

(https://slideplayer.com/slide/1455797/)

· Addressability

Three types of addressability

o Location-addressable

o File addressable

o Content-addressable

Location-addressable- Each of the accessible location units are selected with its numerical memory address. Location-addressable storage usually limits to primary storage

File addressable - Information is divided into files of variable length, and a particular file is selected with human-readable directory and file names. Tertiary and off-line storage use file systems.

Content-addressable - Hardware content addressable memory is often used in a computer's CPU cache. Each individually accessible unit of information is selected based on the basis of (part of) the contents stored there. (https://slideplayer.com/slide/1455797/)

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