Computer Storage Devices

Storage Devices

Topic :

1. Computer Data Storage

2. Types of Storage

3. Storage Device Features

4. Other Examples of Storage Device

Definition:

• A storage device is used in the computers to store the data.

• Provides one of the core functions of the modern computer.

• Physical components or materials on which data is stored are called storage media.

Hardware components that read/write to storage media are called storage devices.

Types of Storage

There are four type of storage

• Primary Storage

• Secondary Storage

• Tertiary Storage

• Off-line Storage

Primary Storage

• Also known as main memory.

• Main memory is directly or indirectly connected to the central processing unit via a memory bus.

• The CPU continuously reads instructions stored there and executes them as required.

• Example

– RAM

– ROM

– Cache

RAM

• It is called Random Access Memory because any of the data in RAM can be accessed just as fast as any of the other data.

• There are two types of RAM

– DRAM (Dynamic Random Access Memory)

– SRAM (Static Random Access Memory)

Static RAM Dynamic RAM

• Faster

• More expensive

• More power consumption

• does not need to be refreshed

• Slower

• Less expensive

• Less power consumption

• needs to be refreshed thousands of times per second

ROM

• This memory is used as the computer begins to boot up.

• Small programs called firmware are often stored in ROM chips on hardware devices (like a BIOS chip), and they contain instructions the computer can use in performing some of the most Basic operations required to operate hardware devices.

• ROM memory cannot be easily or quickly overwritten or modified.

Cache

• Cache is a high-speed access area that can be either a reserved section of main memory or a storage device.

• Most computers today come with L3 cache or L2 cache, while older computers included only L1 cache.

Secondary Storage

• It is not directly accessible by the CPU.

• Computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage.

• Example

– Hard disk

Hard Disk

• The hard disk drive is the main, and usually largest, data storage device in a computer.

• It can store anywhere from 160 gigabytes to 2 terabytes.

• Hard disk speed is the speed at which content can be read and written on a hard disk.

• A hard disk unit comes with a set rotation speed varying from 4500 to 7200 rpm.

• Disk access time is measured in milliseconds.

Tertiary Storage

• Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device.

• It is a comprehensive computer storage system that is usually very slow, so it is usually used to archive data that is not accessed frequently.

• This is primarily useful for extraordinarily large data stores, accessed without human operators.

• Examples

– Magnetic Tape

– Optical Disc

Magnetic Tape

• A magnetically coated strip of plastic on which data can be encoded.

• Tapes for computers are similar to tapes used to store music.

• Tape is much less expensive than other storage mediums but commonly a much slower solution that is commonly used for backup.

Optical Disc

• Optical disc is any storage media that holds content in digital format and is read using a laser assembly is considered optical media.

• The most common types of optical media are

– Blu-ray (BD)

– Compact Disc (CD)

– Digital Versatile Disc (DVD)

CD DVD BD

Capacity 700MB 4.7GB – 17GB 50GB

Example • CD-ROM,

• CD-R

• CD-RW

• DVD-ROM

• DVD+RRW

• DVD-RRW

• DVD-RAM

• BD-R

• BD-RE

Off-line Storage

• Also known as disconnected storage.

• Is a computer data storage on a medium or a device that is not under the control of a processing unit.

• It must be inserted or connected by a human operator before a computer can access it again.

• Also known as disconnected or removable storage.

• Is a computer data storage on a medium or a device that is not under the control of a processing unit.

• It must be inserted or connected by a human operator before a computer can access it again.

• Examples

– Floppy Disk

– Zip diskette

– USB Flash drive

– Memory card

Floppy Disk

• A soft magnetic disk.

• Floppy disks are portable.

• Floppy disks are slower to access than hard disks and have less storage capacity, but they are much less expensive.

• Can store data up to 1.44MB.

• Two common sizes 5 ¼” and 3 ½”.

Zip Diskette

• Hardware data storage device developed by Iomega that functions like a Standard 1.44 floppy drive.

• Capable to hold up to 100 MB of data or 250 MB of data on new drives.

• Now it less popular as users needed larger storage capabilities.

USB Flash Drive

• A small, portable flash memory card that plugs into a computer’s USB port and functions as a portable hard drive.

• Flash drives are available in sizes such as 256MB, 512MB, 1GB, 5GB, and 16GB and are an easy way to transfer and store information.

Memory Card

• An electronic flash memory storage disk commonly used in consumer electronic devices such as digital cameras, MP3 players, mobile phones, and other small portable devices.

• Memory cards are usually read by connecting the device containing the card to your computer, or by using a USB card reader.

Secure Digital card (SD) MiniSD Compact Flash Memory Stick

Multimedia card XD-Picture card

Memory card reader

Storage Device Features

• Volatility

• Accessibility

• Mutability

• Addressability

Volatility

• Two types of volatility

– Volatile Memory

– Non-Volatile Memory

Volatile Memory

• Requires constant power to maintain the stored information.

• The fastest memory technologies.

• All contents are erased when the system's power is turned off or interrupted.

• It has been more popularly known as temporary memory.

Non-Volatile Memory

• Will retain the stored information even if it is not constantly supplied with electric power.

• Nonvolatile memory is the device which keeps the data even when the current is off.

• It is suitable for long-term storage of information.

Accessibility

• Refers to reading or writing data records

• Two types of accessibility

– Random access

– Sequential access

Random Access

• Any location in storage can be accessed at any moment in approximately the same amount of time.

• Such characteristic is well suited for primary and secondary storage.

Sequential Access

• The accessing of pieces of information will be in a serial order, one after the other; therefore the time to access a particular piece of information depends upon which piece of information was last accessed.

• Such characteristic is typical of off-line storage.

Mutability

• Allows information to be overwritten at any time.

• A computer without some amount of read write storage for primary storage purposes would be useless for many tasks.

• Three types of mutability

– Read write storage or mutable storage

– Read only storage

– Slow write, fast read storage

Read Write Storage or Mutable Storage

• Allows information to be overwritten at any time.

• A computer without some amount of read write storage for primary storage purposes would be useless for many tasks.

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.

Slow Write, Fast Read Storage

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

Addressability

• Three types of addressability

– Location-addressable

– File addressable

– Content-addressable

Location-addressable

• Each individually accessible unit of information in storage is selected with its numerical memory address.

File addressable

• Information is divided into files of variable length, and a particular file is selected with human-readable directory and file names.

Content-addressable

• Each individually accessible unit of information is selected based on the basis of (part of) the contents stored there.

• Content-addressable storage can be implemented using software (computer program) or hardware (computer device), with hardware being faster but more expensive option.

• Hardware content addressable memory is often used in a computer's CPU cache.

Other Example of Storage Devices

• Punch card

• Cloud storage

• RAID

Punched Card

• Early method of data storage used with early computers

• Punch cards also known as Hollerith cards

• Containing several punched holes that represents data

• Cloud storage means the storage of data online in the cloud, wherein a data is stored in and accessible from multiple distributed and connected resources that comprise a cloud.

Other Example of Storage Devices

Cloud Storage

• Examples

– Google Drive

– Flickr

– Microsoft Sky Drive

RAID

• RAID is short for redundant array of independent (or inexpensive) disks.

• It is a category of disk drives that employ two or more drives in combination for fault tolerance and performance.

• RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.

• RAID allows you to store the same data redundantly (in multiple paces) in a balanced way to improve overall storage performance.