Backing Storage, Memory and Data Representation Chapter 2 Backing Storage, Memory and Data Representation

What you will learn Storage devices and media Floppy disk, Hard disk, Raid, CDs, DVD, Zip drives and disks, Magnetic tape Backup Memory Main memory – RAM or ROM, Flash memory Data representation Representing numbers, characters, graphics, sound Backing Storage, Memory and Data Representation

Storage devices and media You need backing storage (or secondary memory) to save d___ after the computer is turned off. Your work is stored on the computer as a file, measured in bytes. Backing Storage, Memory and Data Representation

A byte can store one character of data Kbyte -> 1024 bytes Mbyte -> 1024 ____ Gbyte -> 1024 Mbytes Terabyte -> 1024 _____ Backing Storage, Memory and Data Representation

Storage devices and media Storage medium: actual material object e.g. floppy ___ Storage device: item of equipment that handles the use of the medium e.g. floppy disk drive Backing Storage, Memory and Data Representation

Main storage area in a desktop computer is the hard _____ Backing Storage, Memory and Data Representation

Floppy disks Round, flexible magnetic disk Access to the data: slow Storage capacity: 1.44Mbytes Backing Storage, Memory and Data Representation

Hard disks Storage capacity: 300 Gbytes and more Access to the data: very fast Total storage space: (number of readable sides) x (number of cylinders) x (sectors per track) x (bytes per sector) Backing Storage, Memory and Data Representation

Optical disks Backing Storage, Memory and Data Representation

Compact disks (CDs) Storage capacity: 700 Mbytes Access time: faster than a fl____, but slower than hard disk Backing Storage, Memory and Data Representation

Compact disks (CDs) The CD drive has a laser beam in the read/write head, which can read the information on the d___ Backing Storage, Memory and Data Representation

Compact disks (CDs) CD-ROMs -> data can be r___ but not written to them CD-RW -> data can be read from and w____ to Backing Storage, Memory and Data Representation

DVD Digital Versatile Disk Storage capacity: 4.7 Gbytes, but it can carry two layers of data on each of its two sides, thus it can hold up to 18 Gbytes. Backing Storage, Memory and Data Representation

DVD DVD-Video: DVD format for full length movies DVD-Audio: DVD format for carrying audio information DVD-RAM: can write to a special kind of DVD rewritable Backing Storage, Memory and Data Representation

Zip drives and disks Single hard disk that stores data magnetically Storage capacity: 100-250 Mbytes Internal and external zip disks Backing Storage, Memory and Data Representation

Uses of zip disks Uses: -> for transferring large graphics files between computers -> backing up personal computers Backing Storage, Memory and Data Representation

Magnetic tapes Storage capacity: very large due to large amount of surface area Serial access: e.g. if you want to access data at the middle of the tape you need to start at the beginning, therefore slow access Backing Storage, Memory and Data Representation

Magnetic tapes Uses: backing up data One type of magnetic tape is the magnetic tape cartridge Backing Storage, Memory and Data Representation

Backup Backup file: a file is copied in case the original file is lost or destroyed. E.g? Backing Storage, Memory and Data Representation

When to back up data? Back up your files regularly (after some modifications, after the creation of important files, daily or weekly or monthly) and keep it separately from the computer Backing Storage, Memory and Data Representation

Questions? A murderer is condemned to death. He has to choose between three rooms. The first is full of raging fires, the second is full of assassins with loaded guns, and the third is full of lions that haven't eaten in 3 years. Which room is safest for him?  Backing Storage, Memory and Data Representation

HW - answers How many 250 mbyte zip discs would be needed to store 1 gb? One gb= 1024 megabytes 5 zip discs What are the differences between a floppy disc and a hard disc? Floppy disc: smaller, stores less amount of data (1.44), slow access A magnetic tape provides serial access. Explain why this can be a disadvantage. You are not able to go to a specific piece of data without reading the data before it. Describe one use for tape. Backing up data Why do we need to back up data? In case the original file is lost, damages or corrupted. Backing Storage, Memory and Data Representation

Backup Automatic backup of all the files More than one copy should be kept Keep a backup on hand in a fire-proof safe Keep at least one backup in another location Backing Storage, Memory and Data Representation

Backing up a home computer Firstly back up your data on your hard disk Daily you can back up the data on a memory stick At set intervals back up these files to a CD-RW. Every month use a different CD-RW. If the capacity of your data is too large then compress it before store it somewhere else. Backing Storage, Memory and Data Representation

Backing up a home computer Therefore, if a file is lost or corrupted, you can recover it by looking for a copy on floppy disk or zip disk, and then on the most recent CD, or the previous ones. Backing Storage, Memory and Data Representation

Backing up a network Automatically backed up at least one a day Backup copies are often put onto other hard disks, as this speeds up the copying If speed is not important, magnetic cartridges are used which are cheaper Backing Storage, Memory and Data Representation

Backing up a network Software used to take automatic backups keeps track of when and where the backups were taken A systematic method of backups is the ‘ancestral backup system’. This is described in detail in chapter 12 Backing Storage, Memory and Data Representation

Memory – Main memory May be RAM or ROM. These are referred to as IAS (Immediate-access store) RAM Can be written to, read from and edited Data can be accessed in any order (random) Volatile memory – is cleared when the computer is switched off Backing Storage, Memory and Data Representation

Main mem (cont) RAM Can be upgraded, thus more memory modules can be installed in the system unit Backing Storage, Memory and Data Representation

RAM (cont.) Uses: stores data and programs while the computer is running – that is why Ram is referred to as main memory (or primary memory) whereas floppy and hard drives are called backing storage or secondary memory Backing Storage, Memory and Data Representation

Memory - ROM Data in ROM can be read and written to but not changed Data can be accessed in any order Non-volatile memory – it retains what it is stored in it even when the computer is switched off Backing Storage, Memory and Data Representation

Types of ROM PROM[programmable read-only memory ]: at first there is no data, company can put its own information and then lock the data for no future alterations EPROM:[erasable programmable read-only memory] same as PROM but it can erase the data Backing Storage, Memory and Data Representation

Flash memory computer memory primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. Backing Storage, Memory and Data Representation

Flash memory Example applications PDAs laptop, digital audio players, digital cameras and mobile phones. Backing Storage, Memory and Data Representation

Memory – Flash Memory Is a type of EPROM It is often removable A common use of flash memory is the BIOS which makes sure the computer starts up as it should and that all the parts of the computer work together Backing Storage, Memory and Data Representation

Types of flash memory Compact flash: removable, used in digital cameras, PDAs, etc, can store up to 2Gbytes Flash pen devices: are lightweight, fit into your pocket – thus it’s easy to move them around. Used for storing presentations and files Backing Storage, Memory and Data Representation

Addresses and locations Memory is divided into many different locations, each of these can store one byte The computer can find a specific location in memory using its address – unique number Backing Storage, Memory and Data Representation

Words, bits and bytes A word is the amount of data that a computer can directly access at one time It is the natural unit of data used by a particular computer design. A word is simply a fixed-sized group of bits that are handled together by the system. cpu Hard Disk Send one word At a time e.g. number 8 Backing Storage, Memory and Data Representation

Words, bits and bytes Different computers can access one, two or more bytes of data at one time Byte -> 8 signals which can be either on (0) or off (1) A signal is a Binary digIT (bit) Word length: always is stated in terms of bits Backing Storage, Memory and Data Representation

Backing Storage, Memory and Data Representation

Use this presentation + webopedia to answer the questions What is a byte? Why do we have different types of storage devices? Why don’t they sell video games on memory sticks? Cd roms are cheaper Not all pcs have a memory stick port Cd roms cannot be edited. Very easy to copy data on a memory stick How can you represent number 57 in binary (ones and zeros?) What is a back up file? What storage device will a student use to back up his data on a pc? A school use to back up its day to day transactions? Why? Backing Storage, Memory and Data Representation

Data representation How data is represented inside the computer Backing Storage, Memory and Data Representation

Data representation – Representing numbers Base ten: 1,2,3,4,5,6,7,8,9 Backing Storage, Memory and Data Representation

Data representation – Representing numbers cont Base two: the computer uses only two digits {0,1} to represent alphabet letters and other items of information. Since it can take only two values it is a binary digit. Backing Storage, Memory and Data Representation

bytes 8 digits make a byte, and one byte can represent a character (see next slide) See figure 2.9 Backing Storage, Memory and Data Representation

Representing numbers in binary system Backing Storage, Memory and Data Representation

Experiment in Notepad type , "Four score and seven years ago". Save the file The file has a size of 30 bytes on disk: 1 byte for each character. Each character consumes a byte. Backing Storage, Memory and Data Representation

How do we measure memory Backing Storage, Memory and Data Representation

Data representation – Representing characters A character is a symbol that can be represented by a computer (e.g: 1, !, A) Backing Storage, Memory and Data Representation

Questions? Backing Storage, Memory and Data Representation