BWERANYANGI GIRLS’ SECONDARY SCHOOL

S.5 ICT NOTES

SECONDARY STORAGE DEVICES

BY

OUNYESIGA MOREEN

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STORAGE/ BACKUP/ AUXILIARY STORAGE DEVICES

• Storage devices are gadgets used to keep computer held information for future reference.

• Storage devices are divided into two categories;

• Secondary storage devices

• Primary storage devices

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PRIMARY STORAGE / MAIN MEMORY

• This is a storage device used by a computer to hold the currently executing program and its working data.

• Or Memory is a circuitry which is used to store data temporarily with in the CPU while the computer is operating.

• It is composed of magnetic storage devices or semi-conductor devices for example RAM and ROM.

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Types of primary memory

• The system unit contains two types of memory: volatile and non-volatile. The contents of volatile memory are lost when the computer power is turned off.

• RAM is the most common type of volatile memory. Examples of non-volatile memory include ROM, flash memory, and CMOS.

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Random Access Memory (RAM)

• RAM is the memory that is directly available to the CPU.

• RAM is read and write computer memory used to store data temporarily.

• It holds all data and programs in current use.

• RAM can also be defined as memory with the ability to access any allocation in memory in any order with the same speed.

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CHARACTERISTICS OF RAM • RAM is volatile computer memory

• RAM is read and write computer memory.

• RAM stores data temporarily because its contents disappear when the computer is switched off.

• It contents are user defined that the user dictates what is to be contained in the RAM.

• It can be changed or upgraded

• It occupies a bigger portion of the main memory

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Basic types of RAM • Static RAM (SRAM).

• This is very fast compared to dynamic and holds its contents as long as there is power

• Dynamic RAM (DRAM).

• This can only hold its contents for a short while even when power is on.

• Magneto resistive RAM (MRAM), stores data using magnetic charges instead of electrical charges. MRAM has greater storage capacity, consumes less power, and has faster access times.

• Virtual RAM (VRAM): Modern operating systems can use spare storage space on the hard disk as if it is working memory and this is referred to as Virtual memory or Virtual RAM

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Read-only memory (ROM)

• Read-only memory (ROM) refers to memory chips storing permanent data and instructions. That is, the items stored in ROM chips cannot be modified—then, the name read-only.

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CHARACTERISTICS OF ROM

• It keeps data permanently i.e information cannot be deleted

• Memory cannot be upgraded or changed

• Its non-volatile and therefore retains information when power is off.

• It occupies a smaller portion of the main memory

• Its contents can only be read

• Its contents are not user defined ie they come from the manufacturer

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Basic types of ROM • PROM (PROGRAMMABLE READ ONLY MEMORY): This type of memory can only be programmed once after it has been manufactured, such that when its programmed with the instructions stored , it can never be altered e.g. the CD writable. • EPROM (Erasable programmable Read Only Memory) Here the instructions can only be erased once and then reprogrammed and can never be altered e.g. the CD-re-writable • EEPROM(Electronically erasable programmable Read Only

Memory) • This type of memory enables the user to put instruction in

this memory as many times as one may wish. • The instructions will remain in the memory until when one

may wish to have them changed E.g. it is applicable in most color televisions.

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DIFFERENCES BETWEEN ROM AND RAM

RAM ROM

It is Volatile It is non-volatile

It can be read and written to Its contents are read only

It offers temporary storage Offers permanent storage

Its size can be increased Its size may not be increased

Occupies bigger portion of main memory

Occupies smaller portion of memory

Contents are user defined Contents are defined by the manufacturer

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SPECIAL PURPOSE MEMORIES

Apart from RAM and ROM there are several types of special purpose memories found inside the CPU or in the input and output devices.

• Memory cache

A cache is a relatively small block of very fast memory designed for the specific purpose of speeding up the internal transfer of data and software instructions.

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• Flash memory

Flash memory is a chip also that keeps its contents when the power is shut off.

• Complementary Metal-Oxide Semiconductor (CMOS)

CMOS technology uses battery power to retain information even when the power to the computer is off.

CMOS keeps the calendar, date, and time current even when the computer is off.

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• BUFFERS

This is a temporary holding place that may be part of the CPU or built in an input or output device.

• REGISTERS

A register is a temporary storage area used to hold instructions and data currently being processed by the control unit or ALU(Arithmetic Logic Unit).

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Examples of registers are:- • An accumulator: - This temporarily holds the

results of the last step of ALU.

• Instruction Register: - This temporarily holds an instruction just before its interpreted into a form that CPU can understand.

• An address register: - This temporarily holds the next piece of data waiting to be processed.

• Storage Register: - This temporarily holds a piece of data that is on its way to and from the CPU and the main memory.

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Secondary storage devices

• Secondary storage devices store data permanently

• Secondary memory is not directly accessed by the CPU.

• The most common secondary storage devices include: hard disk drive, floppy disk/ diskette drive, CD drives, Zip drives etc

• The most common storage media include; hard disks, flash disks, Tapes, punched cards, memory card etc.

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Common terms related to storage devices.

• A Storage medium is the physical material on which a computer keeps data.

• Capacity is the number of bytes (characters) a storage medium can hold.

• A Storage Device reads and writes data to and from a storage medium.

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• Reading is the process in which a storage device transfers data, from a storage medium into memory.

• Writing is the process in which a storage device transfers data from memory to a storage medium (saving).

• Access time, is a measure of the amount of time it takes a storage device to locate an item on a storage medium.

• Transfer rate is the speed with which data, instructions, and information move to and from a device. Transfer rates for storage are stated in Kbps (kilobytes per second).

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Categories of Secondary Storage

Media There is a wide variety of storage devices in the

following categories.

• Magnetic storage media

• Optical storage media

• Solid-state storage devices

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Magnetic storage media

• The term magnetic storage refers to the storage of data on a magnetized device.

Common examples of magnetic media include:

• Magnetic tape

• Floppy disk,

• Zip and Jazz disks

• Hard disk

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1. Hard disk

This is a data storage device used for storing and retrieving information.

• It uses rapidly rotating plates coated with magnetic material.

• It is fixed in the hard drive which reads and writes on it.

• Hard disks are external (movable) or internal ( immovable found inside the system unit case)

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Advantages of hard disks • Stores huge amounts of data.

• Stores information for a very long period of time.

• Are necessary for supporting the way computers work.

• Store and retrieve data much faster than floppy disks.

• The destruction rate of fixed disks is low since they remain in one position.

• Data stored on the internal hard disk is secure since it can’t be misplaced.

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Disadvantages of hard disks • Any attack of viruses may cause heavy data

loss.

• Hard disks expand and contract with temperature change which may cause data loss.

• The hard disk may fail due violent shaking and vibrations

• It is not easy to transfer data from one machine to another since hard disks are fixed.

• Hard disks are very expensive to buy compared to other storage devices.

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2. Floppy disk (diskette) • This is a small plastic made up of a thin

circular plastic material coated with a magnetic surface where data is stored.

• The most common ones have a storage capacity of 1.44MB

Floppy diskettes are available in four basic sizes

• 8” (8 inch floppy diskette)

• 5.25” (51 4 inch floppy diskette)

• 3.5” (51 2 inch floppy diskette)

• 2” (2 inch floppy diskette for laptops) 18-Jun-21 24

Advantages of using diskettes

• They are portable hence easy transfer of information

• They carry a lot of data compared to their sizes

• Data accessed takes a shorter time

• They are cheap to purchase 18-Jun-21 25

Disadvantages of using diskettes • They are vulnerable to harsh conditions of

storage like temperature changes.

• They can lose data quickly once exposed to a magnetic field

• They store less data compared to any other storage device

• They are expensive in the long run since their destruction rate is high

• They are prone to virus attack which causes data loss.

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Care and maintenance of diskettes • Keep diskettes away from magnet fields, such

as near wire telephones, loud speakers, and other appliances, which contain magnets.

• Do not keep heavy objects on top of the diskettes or drop them on hard surfaces.

• Do not fold or bend diskettes.

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• While labeling or writing on the diskettes use felt tip pen, not pencil or ballpoint pen.

• Do not expose the disk to excessive heat or light.

• Do not pull out the diskette from its drive when the drive light is still on.

• Store them in boxes when not being used.

• Do not splash liquids e.g water e.t.c

• Do not force them into the drive, it should slip in with no resistance

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3. Magnetic tape

• Magnetic tape is a magnetically coated ribbon of plastic capable of storing large amounts of data and information at a low cost.

• Tape storage requires sequential access, i.e. data must be accessed in the order in which it is stored.

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Advantages of using a tape for data storage:

• Can hold thousands of megabytes (MB)

of data depending on the length of the tape.

• Useful for daily backups of all work and programs on a large network.

• Can be set to run automatically during the night.

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Disadvantages of using tapes: • Very slow, as need to wind tape

(perhaps a long way) to find any specific position.

• Random data access is not possible.

• Magnetic Tape Data storage has a limited shelf life of about 2 years only.

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4. Zip disks/drive

• The Zip drive is a medium-capacity

removable disk storage system with

capacities of 100 MB to 750 MB.

• Zip drives fell out of favor for mass portable

storage during the early 2000s due to

emergence of much better USB flash drives

CDs, and DVDs.

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5. The Jazz disks/drive

• The Jazz drive was a removable disk storage system.

• The Jazz disks were originally released with a 1 GB capacity.

• The rising popularity and decreasing price of CDs and DVDs greatly hurt the success of the Jazz Drive and the Jazz line was ultimately discontinued in 2002.

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Optical Storage Media

• These are devices that store data as patterns of dots that can be read using light.

Examples of Optical storage media are;

• Compact discs (CD),

• Digital versatile disc (DVD- ROM),

• CD-rewritable (CD-RW).

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1. The Compact Disk (CD-ROMs)

• Compact Disks are round optical storage medium capable of storing up to 700MB of data

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Advantages of CDs

• They have a high storage capacity (700MB of data)

• They are easily portable hence the transfer of information is easy.

• Their data life is nearly 100% if it has no scratches.

• They are relatively cheap compared to other storage devices.

• They are resistant to virus attacks unlike other storage devices

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Disadvantages of CDs • Their destruction rate is high since a single

scratch may lead to its destruction

• They are prone to scratches which render the entire CD worthless or useless.

• Some CDs are read only, which means that the data can’t be deleted or customized

• Their average access time is slower compared to other storage devices like the hard disk

• CDs may no be read by all computers as some computers do not have CD drives.

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TYPES OF CDs • CD-R (Compact Disk Recordable) They are used for one recording after which it becomes a CD-ROM • CD-RW(Compact Disk Re-writable) They can be written on or re-written more than once. • CD-ROM(Compact Disk-Read Only Memory) Cannot allow the user to write anything on it. • CD-ROMs usually contain the manufacturer’s

instructions on the usage of a particular hardware piece. The user is not allowed to make any changes.

• ROM(Read Only Memory) means that you only read its contents but can’t write on it.

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DVD-ROM

• A DVD-ROM (Digital Video Disc-ROM) is an extremely high capacity compact disc capable of storing from 4.7 GB to 17 GB.

• A DVD-ROM drive or DVD player is required to read a DVD-ROM. Although the size and shape of a DVD-ROM and a CD-ROM are similar.

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Solid-state Storage Media (SSS)

• Solid state storage (SSS)/flash memory: is a type of computer storage media that is made from silicon microchips.

• SSS stores data electronically instead of magnetically

Common examples of Solid-state Storage Media include:

• USB flash drive

• Memory card/Memory Stick

• Smart Card

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1. USB flash drive

• A USB flash drive is a flash memory storage device that plugs in a USB port on a computer.

• USB flash drives are convenient for mobile users because they are small and lightweight enough to be transported in a pocket.

• Current USB flash drives have data storage capacities ranging from 256 MB to 64 GB.

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Memory card/Memory Stick

• Flash memory cards are a type of solid-state media, which means they consist entirely of electronic components and contain no moving parts.

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DISK FORMATTING

• Formatting disks is the process of preparing a new disk for use so that the operating system can recognize it and be able to access it.

Reasons for Disk formatting

• It prepares the new disk for storing data

• It erases un wanted information

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STORAGE TERMS

• A driver is a program that helps a computer system to access the different types of the hardware

• Disk defragmentation is a tool that helps to re arrange scattered files and folders on a storage media so as to speed up access to files and folders

• Disk compression is a tool that helps to compress storage media contents to fit in smaller space so as to create more free space on the media

• Back up data refers to creating copies of data and programs on separate storage device to avoid losing important data in case the computer fails

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• Partitioning disk refers to the process of dividing a large physical into two or more partitions called logical drives

Reasons for partitioning the hard disk

To provide space for data backup

To safeguard specific information from unauthorized access

To speed up computer operations

To facilitate discriminative sharing of resources

• A logical drive is a drive, which can be accessed as if it is a separate disk but in actual sense it is a partition of one physical disk

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• Random access/direct access (machine access) is a term used to describe the ability of a computer to immediately locate and retrieve data from a storage device

• Sequential access (serial access) is a method of retrieving data from a storage device where the device must move through all information up to the location where it is attempting to read or write.

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