ICT Chapter 3.pdf

Chapter – 3 STORAGE DEVICES & MEDIA Secondary Storage Media Chapter 3 – Storage Devices & Media ▪ In this chapter you will learn about: o Backing storage o Why back up data? o Types of access used by secondary storage devices o Types of internal and external “Secondary Storage” dev...

Chapter – 3 STORAGE DEVICES & MEDIA Secondary Storage Media Chapter 3 – Storage Devices & Media ▪ In this chapter you will learn about: o Backing storage o Why back up data? o Types of access used by secondary storage devices o Types of internal and external “Secondary Storage” devices: Magnetic Optical Solid State Input Processing Output Storage Chapter 3 – Storage Devices & Media ▪ Sections 3.1 Backing up of data 3.2 Types of access 3.3 Secondary storage media 3.1.1 What is backing up of data? 3.2.1 Serial access 3.3.1 Magnetic storage media 3.1.2 Why back up data? 3.2.2 Direct access Magnetic tapes Fixed/ Internal hard disk drive (HDD) Portable/ External hard disk drive 3.3.2 Optical storage media CD/ DVD disks 1. CD-ROM / DVD-ROM 2. CD-R / DVD-R 3. CD-RW / DVD-RW 4. CD-RAM / DVD-RAM 5. Blu-ray discs 6. Future optical media 3.3.3 Solid state storage media/ Flash storage Solid state drive (SSD) o ROM o PROM o EPROM o EEPROM Memory sticks/ pen drives Flash memory cards 3.1 Backing up of data ▪ In chapter 1, o Primary storage devices – RAM & ROM o Directly accessed by CPU ▪ Secondary storage devices o Main storage device o Store/ Backup: OS (Operating System) Software/ Program Files (Text, Image, Video, Music, etc.) 3.1.1 What is backing up of data? ▪ Backing up refers to the coping of files/ data to a different medium in case of problem with the main secondary storage device. Coping of files/ data at Different place 3.2.1 Why back up data? 1. Against loss or failure of original secondary storage device o Hardware failure due to fire/ floods etc. o Power losses 2. Against damage caused by hackers 3. Against loss of original files o File being overwritten or delete accidentally 4. Against the effect of virus File access ▪ Read (open) ▪ Write (save) Input Processing Output ▪ Three terms: Write (save) Read (open) o Field o Record Storage o File 3.2 Types of access ▪ Two types of file access Serial Access Direct Access 3.2.1 Serial access ▪ Data is accessed by starting at the beginning and then searched through, in order/ sequence, until the required information is found. ▪ Sometimes called “Sequential Access” ▪ Very Slow data access as need to start beginning blue 3.2.1 Serial access Serial Data Write (Save/ Edit) Old data tape (Master File) 1 2 3 4 5 6 7 8 9 … Update data tape 2 8 (Transaction File) Must Need New data tape (New Master File) 1 1 2 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 … Where serial access is used? ▪ To store a lot of data but where speed of access is unimportant ▪ Used in Batch Processing Systems (Payroll and in the preparation of utility bills) ▪ The way of that serial access works means that all of the data has to be read and there is no danger of missing out someone’s wage payment or bill invoice 3.2.1 Serial access 3.2.2 Direct access ▪ The computer can calculate exactly where the data has been stored and can go straight to it directly (instant access). ▪ Sometimes called “Random Access”. ▪ Very Quickly data access as computer knows the location of data on the storage medium field 2 x record 2 blue Where direct access is used? ▪ Used on most modern storage devices where speed of access is important ▪ Used in situations where fast access to data is important like in Online Booking Systems and Point of Sale (POS) terminals in shops 3.2.2 Direct access ▪ Hard Disk Drive (HDD) ▪ Solid State Drive (SSD) ▪ CD/ DVD Drive ▪ Memory Stick ▪ SD card (Secure Digital Card) ▪ MicroSD card ▪ Primary Storage Devices o RAM & ROM 3.3 Secondary Storage Media ▪ Storage media is the part that holds data ▪ Storage device is the machine that reads/ writes data to and from the media ▪ Storage media can either be: o Internal – inside the computer (System Unit) o External – plugged in to the computer form the outside ▪ Storage media is “permanent storage” and will hold data even when the computer is power off Storage Capacity ▪ Maximum amount of data can be stored ▪ Measured in ‘Bytes’ (8 bits = 1 Bytes) o Bits are shorts for ‘binary digits’. This is the smallest unit of data that can be stored. Each ‘bit’ is represented as a binary number, either 1 or 0 o A single character takes up 1 Byte of storage (8 bits) Storage Capacity Units ▪ Typically, storage sizes or file sizes are measured in kilobytes (KB), megabytes (MB), gigabytes (GB), and terabytes (TB) Unit Symbol Information Number of Bytes Power of 2 Example Smallest unit of Bit b data (1 or 0) Byte B 8 bits = 1 byte 1 20 Kilobyte KB 1024 bytes = 1 KB 1 000 210 half a page of text Megabyte MB 1024 KB = 1 MB 1 000 000 220 500 pages of text Gigabyte GB 1024 MB = 1 GB 1 000 000 000 230 500,000 pages of text Terabyte TB 1024 GB = 1 TB 1 000 000 000 000 240 1, 000, 000 thick books Petabyte PB 1024 TB = 1 PB 1 000 000 000 000 000 250 Exabyte EB 1024 PB = 1 EB 1 000 000 000 000 000 000 260 Zettabyte ZB 1024 EB = 1 ZB 1 000 000 000 000 000 000 000 270 Yottabyte YB 1024 ZB = 1 YB 1 000 000 000 000 000 000 000 000 280 3.3 Secondary Storage Media ▪ Three main types of storage media: 3.3.1 Magnetic Storage Media Storage 3.3.2 Optical Storage Media Media 3.3.3 Solid State Storage Media 3.3.1 Magnetic Storage Media ▪ Holds data magnetically ▪ Surface area of the media are magnetised so that they can hold ‘bits’ of data ▪ The device that read the media can also read the bit’s, held on the surface area Hard Disk Magnetic Tape 3.3.1 Magnetic Storage Media ▪ Four types of Magnetic Storage Media 1. Magnetic Tape 2. Floppy Disk 3. Fixed Hard Disk Drive 4. Portable Hard Disk Drive Magnetic Tape ▪ Oldest forms of computer data storage ▪ Thin strip of magnetic coated plastic which is wrapped onto a reel ▪ Data is stored on the magnetic plastic in the form of 1 and 0 ▪ Data is written and read form in sequence (Serial Access) ▪ Very slow data access rate Usage ▪ Extremely large amounts of data need to be backed up ▪ Speed of reading/ writing of data is NOT a priority Magnetic Tape Advantages Disadvantages ▪ Less expensive than the equivalent capacity ▪ Very slow data access/ transfer (Reading Hard Disk Drive data back from the tape is slow) ▪ Very robust (not easily damage) ▪ Needs another tape to update data ▪ Very large storage capacities (up to 185 TB) o Exp: original tape + changes tape = updated tape Magnetic Tape Floppy Disk ▪ Old method of portable data storage ▪ Data is held on a thin plastic disc ▪ Data is written/ read by floppy disk drive which rotates the disk ▪ Using Direct Data Access method, but data transfer rates are very slow ▪ Maximum storage capacity is 1.44 MB (700 pages of text) ▪ Disc is protected by retractable metal sleeve and hard plastic casing ▪ A small notch provides write protection Floppy Disk Advantages Disadvantages ▪ Cost very little to buy ▪ Very low storage capacity when compared ▪ Can be write protected easily which to other media (1.44 MB) protects against accidentally copying over ▪ Very few modern computers have floppy files disc drives ▪ Very small, light and easy to carry ▪ Very delicate and easy to damage (portable) ▪ Slow data transfer rate Floppy Disk Fixed/ internal hard disk drive (HDD) ▪ Available on all computers and is the main method used for data storage ▪ Very fast Direct access of files and very large storage capacities ▪ Uses a read/write head to write and read data from it ▪ Disk surface (Platter) coated in magnetic film, storage is done by altering binary codes to 1s or 0s Fixed/ internal hard disk drive (HDD) Fixed/ internal hard disk drive (HDD) Fixed/ internal hard disk drive (HDD) Usage ▪ Used to store operating systems (OS) and working data/ flies ▪ Used for storing application software ▪ Real time systems and online systems used fixed hard drives ▪ Used in file servers for computer networks Fixed/ internal hard disk drive (HDD) Advantages Disadvantages ▪ Very fast data transfer rate and fast access ▪ Can be easily damaged if the correct times to data shutdown procedure is not carried out, this ▪ Have very large memory capacities can lead to data losses ▪ Very easy to update/ delete files ▪ They lack portability ▪ They have moving parts Portable Hard Disk Drive (External HDD) ▪ Like fixed hard disks but are usually connected externally via Universal Serial Bus (USB) ▪ Direct data access ▪ Design to transportable ▪ Protective casing to avoid physical damage Portable Hard Disk Drive (External HDD) Usage ▪ Like Fixed hard drives, they are used to store large file ▪ Used as portable backup systems ▪ Used to transfer data, files and software Portable Hard Disk Drive (External HDD) Advantages Disadvantages ▪ Portable ▪ Easy to steal ▪ Data access time and transfer rate is very ▪ Easy to misplace fast ▪ Easy to damage ▪ Large memory capacities ▪ More expensive than other forms of storage ▪ Can be used to transfer data, files and software ▪ Small and light with protective casing 3.3.2 Optical Storage Media ▪ All the mediums that use a light source to read/ write data onto a disc 3.3.2 Optical Storage Media 3.3.2 Optical Storage Media ▪ Eight different types of optical storage media 3.3.2 Optical Storage Media ▪ The data store in “Pits” and “Bumps” (Land) on the special track 3.3.2 Optical Storage Media ▪ Laser beam produces heated spots and unheated spots 3.3.2 Optical Storage Media ▪ The device that reads the media can read the data by shining a lower powered laser over the dots ▪ The process of writing data onto the disc surface with the laser beam is called “Burning” Write (Burning) Read (Reflection) Reflect = 1 No reflect = 0 3.3.2 Optical Storage Media ▪ Use a thin layer of an organic dye as the recording media ▪ DVDs also use an additional silver alloy or gold reflector 3.3.2 Optical Storage Media 3.3.2 Optical Storage Media 3.3.2 Optical Storage Media CD-ROM / DVD ROM ▪ Read only memory – cannot be overwritten ▪ Data is stored as a series of pits and lands formed by a laser beam etching the surface at manufacturing stage ▪ CD-ROM’s and DVD-ROM’s are bought with pre-loaded data already on them ▪ Maximum storage capacity o CD-ROM → up to 800 MB o DVD-ROM → 4.7 GB Uses Store music files and software. Very large storage capacity and are used to store films. CD-ROM (Music tracks, Software, etc.) DVD-ROM (Movies, Modern games, Multimedia encyclopedias, etc.) CD-ROM / DVD ROM Advantages Disadvantages ▪ Holds more data than floppy disks ▪ Data transfer rate and data access time are ▪ Less expensive than hard disk drives slower ▪ Cannot accidentally erase ▪ You cannot add your own files to the discs because they are both read only ▪ Very portable as they are small and light ▪ Hold far less data hard disk drives or memory sticks CD-R / DVD-R ▪ The letter ‘R’ means the disc is recordable only once and then it becomes ROM ▪ Data can be added to the disc (once) but NOT eased when it is on there ▪ Use a thin layer of an organic dye as the recording media ▪ DVDs also use an additional silver alloy or gold reflector ▪ Maximum storage capacity o CD-R → 700 MB o DVD-R → 4.7 GB CD-R / DVD-R Uses ▪ They are used for home recording of music (CD-Rs) and films (DVD-Rs) ▪ They are used to store data for later use ▪ Used in applications where it is necessary to prevent the deletion or over-writing of important data CD-R / DVD-R Advantages Disadvantages ▪ Cheaper than RW disks ▪ Can only be reordered once ▪ Once burned, data is impossible to ▪ If an error occurs during burning, the disc is accidentally delete because the disc damaged and must be thrown away becomes read only (wasted) ▪ Easy to transport ▪ Not all CD/DVD players and can read CD-R ▪ Very slow data transfer rate CD-RW / DVD-RW ▪ ‘RW’ means that these disks are re-writable media can be written over several times ▪ Unlike CD-R/DVD-R they don’t become ROMs ▪ The recording layer uses a special phase-changing metal alloy ▪ The alloy can switch between crystalline and amorphous (non-crystalline) phases, thus changing its reflectivity to light, depending on the laser beam power ▪ Spots are produced which can be read by a laser ▪ System allows data to be written, erased and re-written many times ▪ Maximum storage capacity o CD-RW → 700 MB o DVD-RW → 4.7 GB CD-RW / DVD-RW Uses ▪ CD-RWs and DVD-RWs are used to record radio and television programs ▪ They are used in closed circuit television (CCTV) systems ▪ Used to make backups of computer files CD-RW / DVD-RW Advantages Disadvantages ▪ Can be reused many times ▪ Relatively expensive media ▪ Different file formats can be used each time ▪ More expensive than CD/ DVD-R ▪ Less wasteful than R format since files or ▪ Possible to accidentally overwrite data can be added at a later stage ▪ Data transfer is very slow compared to HDD DVD-RAM (DVD- Random Access Memory) ▪ Unlike other CD and DVD formats, DVD-RAMs have several discrete concentric tracks rather than a single spiral track ▪ Gives them advantage that writing, and reading can occur at the same time ▪ Makes it possible to watch an already recorded television program at the same time as a different program is being recorded ▪ Recording layer is made from similar phase- changing material to that used in RW technology ▪ Shiny and dull marks represent data to a computer where they are interpreted DVD-RAM Uses ▪ DVD-RAMs are used in recording devices such as satellite receivers to allow simultaneous recording and playback ▪ They are used in camcorders to store films ▪ Maximum storage capacity o 4.7 GB o 9.4 GB (Dual side) DVD-RAM Advantages Disadvantages ▪ Have a long life (30 years) ▪ DVD-RAMS are not as compatible as R or ▪ Can be re written on more than the DVDRWs RW, many systems will not recognize this (100,000 times) format ▪ Very reliable as they have built in ▪ More expensive than DVD-RW verification software to ensure accuracy of data ▪ Access is very fast ▪ No need to finalize the disk ▪ Very large capacities ▪ Ability to read and write data at the same time Blu-Ray Discs ▪ Used blue laser, rather than red laser ▪ The blue laser color is why the name ‘Blu-ray’ was used ▪ Blu-ray RW can be rewritten to in much the same way as RW disks ▪ Blu-ray storage capacities o 25 GB o 50 GB o 100 GB Uses ▪ Blu-ray disks are used in home video consoles ▪ Used for storing and playing back films ▪ PCs can use this technology for data storage or backing up hard drives ▪ Camcorders can use this media to store film footage Blu-Ray Discs Advantages Disadvantages ▪ Very large storage capacity ▪ Disks are relatively expensive ▪ Data transfer rate is very fast ▪ Blu-ray disks still have encryption problems ▪ Data access speed is faster than with other optical media Flash Memory ▪ ROM (Read Only Memory) o type of non-volatile memory ▪ PROM (Programmable read-only memory) o one-time programmable ▪ EPROM (Erasable programmable read-only memory) o can be erased by exposure to strong ultraviolet light (typically for 10 minutes or longer) ▪ EEPROM (Electrically erasable programmable read-only memory) o can be electrically erased, then rewritten electrically, 1. EAROM (Electrically alterable read-only memory) is a type of EEPROM that can be modified one bit at a time. Writing is a very slow process and again needs higher voltage (usually around 12 V) than is used for read access. 2. Flash memory is a modern type of EEPROM invented in 1984. Flash memory can be erased and rewritten faster than ordinary EEPROM. Modern NAND flash makes efficient use of silicon chip area. 3.3.3 Solid State Storage Media ▪ Solid state systems control the movement of electrons within a microchip: if the transistor conducts a current, this is equivalent to a 1, otherwise it is a 0 ▪ Have no moving parts, consume much less power and are extremely robust ▪ Used primarily as removable storage devices and are collectively known as flash memory Solid State Drive (SSD) ▪ Supports reading/writing data & maintains stored data in a permanent state even without power ▪ Functions much like a hard drive but different tech ▪ Built with an array of semiconductors that form its memory and operated using an integrated circuit Uses ▪ Used to store operating systems and working data ▪ Used for storing application software ▪ Used in file servers for computer networks Solid State Drive Advantages Disadvantages ▪ Faster than hard disks because they do not ▪ More expensive than hard disks need to ‘spin up’ the disk ▪ Have a smaller capacity than modern hard ▪ Robust because no mechanical parts disks ▪ Read performance is fast even when data ▪ Lower number of write cycles causing fragmented performance to diminish over time ▪ Less susceptible to data loss ▪ Lighter, quieter and require less power than hard disks Flash Drive (Memory stick/ Pen drive) ▪ Otherwise called pen drive/memory stick/USB stick ▪ Can store several GBs of data and use solid state technology ▪ Connected to a computer through USB port and power to operate drawn from host computer ▪ Some expensive software increasingly uses these storage methods as a form of security Uses ▪ Used to transport files between computers ▪ Used as a security device – a dongle – to prevent software piracy Flash Drive (Memory stick/ Pen drive) Advantages Disadvantages ▪ Very compact and portable media ▪ Not possible to write protect the data and ▪ Very robust files ▪ Compatible with almost any computer ▪ Small physical size and are easy to lose. ▪ Large storage capacities ▪ Lower storage capacity than hard disk Flash Drive (SD card /Micro SD card) ▪ Secure Digital Cards (SD card) ▪ Smaller version → Micro SD card ▪ Form of EEPROM ▪ Use solid state technology (have no moving parts) Uses ▪ Used to transport files between computers ▪ Store photos on digital cameras ▪ A wide range of electronic devices, laptops, mobile phones, tables and mp3 players Flash Drive (SD card /Micro SD card) Advantages Disadvantages ▪ Very small (easy to transport) ▪ Not possible to write protect the data and ▪ Easy to connect to mobile devices through files SD card slots ▪ Small physical size and are easy to lose. ▪ Robust ▪ Lower storage capacity than hard disk Comparison of Storage Media ▪ Amount of data stored (capacity) ▪ Speed of data access ▪ Portability ▪ Cost Storage Capacity Data access rate Portability Cost