CompTIA A+ 220-701 - Storage Devices - Part 3 of 3

This video explain some kind of renovable storage and the uses.

MEMORY CARD


An electronic flash memory storage disk commonly uses in electronic devices such as digital camera, mp3 players, mobile phones and  others. Memory cards are usually read by connecting the device with the card to the computer or by using a USB cable.

FLASH DRIVE


Is a small, portable flash memory card that plugs into a computer USB. USB flash drives have less storage capacity than a external hard drive, but they are small and more durable because they do not contain any internal moving parts.

Some examples of storage device

HARD DISK  


A magnetic disk on which you can store data. The term hard disk is used to distinguish it from a soft, or floppy disk.There are two types of hard disk:


1.Hard disks fixed internally 
2. External hard disks fixed to USB

 


FLOPPY DISK 


A soft magnetic disk. In contrast to hard disk, floppy disk are portable, because you can remove them from a disk drive. Floppy disk are slower to acess than hard disk and have less storage capacity than hard disk.

CD's 

Is a compact disk with oe or more metal layers capable ofstoring digital information. Is used for music industry to store digital recordings.  And CD roms are used to store computer data.

DVDs

Is a type of optical disk technology smilar to the CD rom. DVDs are commonly used as a medium for digital representation of movies and other multimedia presentations that combine soond with graphics.

Portable storage devices are more common every day, every time the manufactured with greater capacity and more manageable in size. I can mention: CDs, DVDs, audio cassettes, discs 3, 5, memory cards, photographic reels, USB, flash memory.

Data Storage Equipment

Any input/output equipment may be considered data storage equipment if it writes to and reads from a data storage medium. Data storage equipment uses either:

• portable methods (easily replaced),
• semi-portable methods requiring mechanical disassembly tools and/or opening a chassis
• inseparable methods meaning loss of memory if disconnected from the unit.

Primary storage

Direct links to this section: Primary storage, Main memory, Internal Memory.

Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner. 

Secondary Storage

Secondary storage (also known as external memory or auxiliary storage), differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile.

Some other examples of secondary storage technologies are: flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip drives.

Tertiary storage

Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands. 

Typical examples include tape libraries and optical jukeboxes.When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library

Large tape library. Tape cartridges placed on shelves in the front, robotic arm moving in the back. Visible height of the library is about 180 cm.

Characteristic of Storage

Storage technologies at all levels of the storage hierarchy can be differentiated by evaluating certain core characteristics as well as measuring characteristics specific to a particular implementation. These core characteristics are volatility, mutability, accessibility, and addressibility. For any particular implementation of any storage technology, the characteristics worth measuring are capacity and performance.

Volatility

Non-volatile memory

Will retain the stored information even if it is not constantly supplied with electric power. It is suitable for long-term storage of information. Nowadays used for most of secondary, tertiary, and off-line storage.

Volatile memory

Requires constant power to maintain the stored information. The fastest memory technologies of today are volatile ones.

Mutability

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. 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 (Write Once Read Many) allows the information to be written only once at some point after manufacture. These are called immutable storage. Immutable storage is used for tertiary and off-line storage. Examples include CD-ROM and CD-R.

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. Examples include CD-RW andflash memory.

Accessibility

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.

Capacity

Raw capacity

The total amount of stored information that a storage device or medium can hold. It is expressed as a quantity of bits or bytes (e.g. 10.4 megabytes).

Memory storage density

The compactness of stored information. It is the storage capacity of a medium divided with a unit of length, area or volume (e.g. 1.2 megabytes per square inch).

Performance

Latency

The time it takes to access a particular location in storage. The relevant unit of measurement is typically nanosecond for primary storage, millisecond for secondary storage, andsecond for tertiary storage.

Throughput

The rate at which information can be read from or written to the storage. In computer data storage, throughput is usually expressed in terms of megabytes per second or MB/s, though bit rate may also be used.

DEFINITION

A data storage device is a device for recording (storing) information (data). Recording can be done using virtually any form of energy, spanning from manual muscle power in handwriting, to acoustic vibrations in phonographic recording, to electromagnetic energy modulating tape and optical discs.

A storage device may hold information, process information, or both. A device that only holds information is a recording medium. Devices that process information (data storage equipment) may both access a separate portable recording medium or a permanent component to store and retrieve information.