Tuesday 19 th October, 2015 Information Technology

Secondary Storage At the end of this lesson you will be able to: Categorize the different types of secondary storage media Explain how information is accessed from different types of secondary storage media Identify portability and significance

Secondary Storage At the end of this lesson you will be able to: Select secondary storage media in terms of speed Select secondary storage media in terms of capacity Choose which secondary storage media are suited for our everyday needs.

Secondary Storage

Magnetic Media/ Devices

Secondary Storage Magnetism VideoMagnetism Video (2.20)

Secondary Storage Magnetic Tape

Secondary Storage Magnetic Tape – A secondary storage medium in which data are stored by means of magnetised and unmagnetised spots on tape; can store information only sequentially or serially.

Secondary Storage Storage of Data on Magnetic Tape GAPGAP Record GAPGAP GAPGAP Block Separates Blocks of Data

Secondary Storage Advantages – 1. It is low in cost 2. Relatively stable storage medium 3. Reusable meaning its contents can be erased in order to store new information 4. Capacity – Can store between 200MB to 10 GB 5. Often used as backup e.g. school network

Secondary Storage Disadvantages – 1. It stores information sequentially or serially which causes it to be slow 2. Records cannot be updated in place (‘in situ’). 3. Tape must be stored in a suitable environment (tape can age and crack over time and storage environment must be controlled i.e. tapes placed upright, cool and low humidity)

Secondary Storage Floppy Disc – A flexible, inexpensive magnetic disc used as secondary storage medium; primarily used with PCs.

Secondary Storage Floppy Discs

Secondary Storage Storage of Data on Floppy Disc Sector Track Data Records Inter-sector Gap

Secondary Storage Advantages – 1. They are very cheap 2. Small, lightweight and convenient 3. Exchangeable

Secondary Storage Disadvantages – 1. Floppies are vulnerable – short shelf life, susceptible to dirt and dust 2. Time consuming if access is needed to view many files over short period of time 3. Low storage capacity, 1.44 MB 4. Becoming outdated

Secondary Storage Hard Disc Drive, HDD – Magnetic hard disks are thin metallic platters with an iron oxide coating. Several discs may be mounted together on a vertical shaft where they rotate at speeds approx. 3,500 to 7,200 rpm.

Secondary Storage Hard Disc Drive, HDD

Secondary Storage HDD Schematic

Secondary Storage Advantages – 1. Individual records can be accessed directly, within milliseconds e.g. in an airline reservation system or customer information systems 2. Very high capacity, at low cost (per character stored). Can start from 120GB upwards.

Secondary Storage Advantages – 4. Disc packs are convenient to handle and store 5. Disc storage permits records and pieces of related data to be organised and combined easily 6. Vacuum packaged

Secondary Storage Disadvantages – 1. Hard Discs are more expensive than most secondary storage devices viz. tapes, floppy discs, CDs and DVDs. 2. Susceptible to dust, static electricity, head crashes 3. Backup is required.

Secondary Storage Optical Media/ Devices

Secondary Storage CDs and DVDs

Secondary Storage Optical Disc – A disc on which data are recorded and read by laser beams rather than by magnetic means. The laser burn microscopic pits in a spiral track when writing in which a pit can be a “0” while a clear area a “1”. Such discs can store data from 700 MB as in CDs to 4.7 GB as in DVDs.

Secondary Storage Cross-section of an Optical Disc

Secondary Storage Operation of an Optical Disc

Secondary Storage Compact Disc, CD – An optical disc system used with PCs. Massive quantities of data can be stored in a highly compact form e.g. data, music and videos. Available in CD-ROM/R/RW

Secondary Storage Compact Discs

Secondary Storage Digital Video Disc, DVD – Another optical disc of even higher capacity, with the ability to store data starting from 4.7 GB, enough to store a full-length movie. Available in DVD+R, DVD+RW, DVD-R, DVD-RW and DVD-ROM.

Secondary Storage Advantages – 1. They have massive storage capacities 2. High-quality pictures and sounds can be achieved without noticeable deterioration, even after continuous use 3. Information can be retrieved quickly by direct access

Secondary Storage Advantages – 5. Discs are coated against dust and most scratches 6. Relatively cheap and easy to access 7. Reliable.

Secondary Storage Disadvantages – 1. Data tends to become corrupted on certain types of discs 2. Not all writeable software supports standards for writing

Secondary Storage Solid State Media/ Devices

Secondary Storage Solid-state device- Electronic device in which electricity flows through solid semiconductor crystals or contains a EEPROM chip semiconductor

Secondary Storage

Flash Drive – A small, portable flash memory card that plugs into a computers. USB port and functions as a portable hard drive. USB flash drives are touted as being easy-to-use as they are small enough to be carried in a pocket and can plug into any computer with a USB drive.flash memoryUSBporthard drive

Secondary Storage Flash Drive cont’d – USB flash drives have less storage capacity than an external hard drive, but they are smaller and more durable because they do not contain any internal moving parts.

Secondary Storage

Flash Memory – Flash memory is used for easy and fast information storage in computers, digital cameras and home video game consoles. It is used more like a hard drive than as RAM.digital camerasvideo game consoleshard driveRAM

Secondary Storage Flash Memory cont’d – In fact, flash memory is known as a solid state storage device, meaning there are no moving parts -- everything is electronic instead of mechanical.

Secondary Storage

Solid State Drive, SSD – A traditional hard disk drive (HDD) consists of a spinning disk with a read/write head on a mechanical arm. An SSD, on the other hand, has an array of semiconductor memory organized as a disk drive, using integrated circuits (ICs) rather than magnetic or optical storage media.

Secondary Storage Recap – Categorize the different types of secondary storage media Explain how information is accessed from different types of secondary storage media Identify portability and significance

Secondary Storage Recap – Select secondary storage media in terms of speed Select secondary storage media in terms of capacity Choose which secondary storage media are suited for our everyday needs.

Secondary Storage Thank you for being a great class and have a good afternoon! Please check google drive for today’s lesson.