IT220 Network Standards & Protocols Unit 1: Chapter 1 Introduction to Computer Data
Objectives Identify the major needs and stakeholders for computer networks and network applications. Describe how digital devices store data. Describe the differences between input and output devices. 2
Various Types of Computer/Computing Devices 3 Figure 1-1
Introducing Data and Information, Bits and Bytes Computers use binary digits (bits) to record information electronically Bits represent either value of 0 or 1 Bit is smallest unit of data computers work with Computers work with multi-digit binary numbers 1. Nibble 2. Byte 3. Word 4. Doubleword 4
Nibble, Byte, Word, Double Word 5 Figure 1-2
Kilobyte, Megabyte, Gigabyte, Terabyte Term Size (Bytes) Size (2 N Bytes) Rounded by Size (Bytes) Kilobyte 1024 2 10 1,000 Megabyte 1,048,576 2 20 1,000,000 Gigabyte 1,073,741,824 2 30 1,000,000,000 Terabyte 1,099,511,627,776 2 40 1,000,000,000,000 6 Table 1-1
Random Access Memory (RAM) Physically exists as set of microchips installed on plastic card (memory module) Central Processing Unit (CPU) uses RAM like people use notepad 1. Stores binary value so can use it later 2. Can read data from RAM to recall value stored earlier CPU sends electrical signal over bus (electrical pathway) to communicate with RAM 7
Random Access Memory (RAM) (cont.) RAM uses address for each unique memory location where byte can be stored To write to RAM: CPU sends signal to RAM over the bus to write (store) value into byte of RAM 1. Address in RAM 2. Value to be written To read from RAM: CPU uses similar process (see example in Figure 1-3 on next slide) 8
CPU Reads Byte 4 from RAM The CPU uses the same bus to read the current value of a byte in RAM as it does to send a message to RAM. The read request lists the address of the particular byte, asking for its value. RAM returns the binary value stored at that address. 9 Figure 1-3
Writing Individual Bits in Byte 4 of RAM RAM circuitry sends a slightly different electrical input to the bits that need to store a 1 versus a 0 to control the capacitors. Essentially, RAM chooses one of two inputs to each bit, which results in either a full or partial charge in the capacitor, which in turn represents either a 1 or 0, respectively. 10 Figure 1-4
Representing Information Using Bytes of Data Data: Focused on bits and bytes Information: Focused on meaning and context Text Character Sets (character encoding scheme): Lists all text characters available on computer with matching binary value 11
Converting Binary 01111011 to Decimal 123 1) Multiply the decimal digit value times the binary value in each of the eight columns. 2) Add the eight numbers found from the previous step (bottom row in the table). 12 Figure 1-7
Converting Decimal 123 to Binary 01111011 1) If countdown > decimal digit value: a. Write a 0 for the binary digit b. Copy the countdown to the next bit position 2) If the countdown <= decimal digit value: a. Write a 1 for the binary digit b. Subtract the decimal digit value from the countdown, and place in the next bit position 13 Figure 1-8
Unsigned Integers in Computers, Various Sizes Size of Storage Number of Bits Range, From 0 to 2 N 1 Byte 8 0-255 2 8-1 Word 16 0 65,535 2 16-1 Doubleword 32 0 4,294,967,296 2 32-1 NOTE: Appendix B, Numeric Reference Tables, includes a table of decimal numbers 0-255, along with their 8-bit binary equivalent values. 14 Table 1-2
Permanent Storage for Bits, Bytes File Systems Allow computer to store bytes of single file in many locations, while still keeping track of them Files Named set of related bytes of data that OS stores as single entity (based on name) to easily refer to data 1. Unique name for each file 2. Keep bytes in order 3. Can be stored on any kind of physical storage device 4. Can be copied or moved to other devices and stored there as well 15
Permanent Storage for Bits, Bytes (cont.) File types examples 1. Song (.mp3,.wav) 2. YouTube video (.swf,.mpeg,.avi) 3. Text file (.txt,.rtf) 4. This PowerPoint presentation (.ppt.,.pptx) 5. High-resolution image from space telescope (.png,.jpg) 16
The Process of Storing Files 1. Application knows addresses in RAM that hold contents of document 2. When user clicks save and names the file, OS sends file contents over bus to storage location (drive) 3. Drive stores file 17 Figure 1-9
File Systems and Directories Directory - Part of file system used to organize files into hierarchy, keeping similar files together. 18 Figure 1-10
Mapping Files and Directories to File Content (cont.) 1. CPU attempts to read file /notes/mydoc (file mydoc in /notes folder) 2. File System supplies file information from directory, including pointer to location on disk where file physically resides 19 Figure 1-13
Mapping Files and Directories to File Content (cont.) 3. CPU reads file s contents from location discovered in previous step; i.e., CPU gets copy of bytes held at that particular place on disk 4. Disk drive transfers bytes of entire 1 KB file to CPU (CPU stores file in RAM so application can work with it) 20 Figure 1-13
File System Miscellany File system secures data; particularly useful for computers that have multiple users 1. OS may be able to assign rights per subdirectory or per file 2. Rights typically give user right to read, write (to modify file s contents), and/or to delete file 21
File System Miscellany (cont.) OS defines file system so type of physical storage device does not matter 1. All file system concepts apply whether storage device is disk drive, drive with removable media (e.g., DVD drive or a flash drive), or any kind of storage media 2. Important to take time to look more closely at those devices 22
Hard Disk Drives Most common long-term computer storage devices today Store a lot of data & do not cost a lot of money Make data available all the time Storage topics 1. Hard Disks vs. Floppy Disks 2. Hard Disk Drive Internals 3. Writing Data to Sectors, Tracks 4. Using Bus to Communicate 23
Hard Disks vs. Floppy Disks (cont.) http://www.wdc.com/global/images/overview/en/ov_intdesktop.jpg 24 Figure 1-14b
Writing Data to Sectors, Tracks A platter has many locations that can hold magnetic charges. Physically, these locations exist in concentric circles, with each circle called a track. A sector refers to a subset of a track, as shown in the figure. 25 Figure 1-15
Writing Data to Sectors, Tracks (cont.) The OS (running on the CPU) has already discovered four currently-unused sectors on a platter of a hard disk. The OS next tells the drive to prepare to write the file by reserving those sectors so no other application or process tries to use them. The CPU then delivers the file contents to be written in those reserved sectors. Four sectors of 256 bytes each will hold the entire 1KB file. 26 Figure 1-16
Using a Bus to Communicate Bus Electrical pathway between internal components of computer CPU uses bus to connect to hard drive (uses different electrical circuits to pass control information versus data) Bus creates one or more electrical circuits between motherboard and disk drive 1. To send bit value of 0, device varies electrical current in some pre-determined way 2. To send bit value of 1, device varies electrical current in some other way 27
Break Take 10 28
Other Permanent Storage Devices Many competing types of permanent storage devices Different devices use different mechanisms to read and write data 1. USB Flash Drives 2. CD and DVD Drives 29
Key Comparison Points, Permanent Storage Short Description Internal or External? Removable Media? Solid State? Longer Description Does the device sit inside the computer, where is stays, or does it connect externally, so it can be easily moved between computers? Can you remove the media from the drive, and insert new blank media to record more data? Solid state means that the device has no moving parts; moving parts make it more likely to break over time Hard Disk Drive (HDD) Both No No 30 Table 1-3
Key Comparison Points, Permanent Storage (cont.) Short Description Read/Write Speed vs. Internal HDD Price/GB Compared to HDD Longer Description How fast do reads and writes occur, compared to an internal Hard Disk Drive (HDD)? How much does a typical device cost, per GigaByte (GB) of storage, relative to a hard disk drive (HDD)? Hard Disk Drive (HDD) N/A N/A 31 Table 1-3
USB Flash Drives USB flash drives provide permanent and portable storage. However, instead of using a drive that stays in the computer, with removable media, the entire (somewhat small) USB flash drive can be connected to a computer using a plug on the side of the computer. http://www.kingston.com/flash/default.asp 32 Figure 1-17
Key Comparison Points, USB Flash and Hard Disk Drives Short Description Hard Disk USB Flash Drive Internal or External? Both External Removable Media? No Yes * Solid State? No Yes Read/Write Speed vs. Internal HDD N/A Slower Price/GB, at Publication, vs. HDD N/A More Expensive * Media cannot be removed from the drive, but the entire drive can be removed from the computer. Note: Table information may change over time, but as of publication, USB flash drives work well for convenience, portability, and low price; but are too slow and too small to be used to replace a hard disk drive. 33 Table 1-4
CD and DVD Drives A Short History For almost first 100 years, phonograph records distributed music Phonograph (record player) played records Needle on spinning record followed grooves to play different sounds; coined the word Groovy Magnetic tape replaced vinyl albums 1. 8-track tape 2. Cassette tape 34
CD and DVD Drives A Short History (cont.) These technologies used analog technology 1. Recordings made sounds analogous to sound waves onto media CD became first common digital consumer music technology 1. Digital audio storage represents each sound with bit pattern 35
CD and DVD Drives A Short History (cont.) DVDs followed similar history as CDs but with video VHS tape first popular format to buy movies to view at home 1. Analog magnetic tape technology Video world migrated from VHS tapes to DVDs (like CDs but for movies) DVDs used many of same ideas as CDs but with more storage capacity CDs and DVDs store bits by using optics (light) 1. Optical Disc Drives 36
CD and DVD Drives Compact Disc (CD) and Digital Video Disc (DVD) drives provide an entirely different class of computer storage as compared with hard disk drives and USB flash drives. http://www.samsung.com/us/images/article/heromodule_dvdwriter.jpg 37 Figure 1-19
Key Comparison Points, USB Flash and Hard Disk Drives Short Description Hard Disk USB Flash Drive Optical Disc Internal or External? Both External Both Removable Media? No No1 Yes Solid State? No Yes No Read/Write Speed vs. Internal HDD N/A Slower Slower Price/GB, at Publication, vs. HDD N/A More Expensive N/A2 The last row of the table brings up an interesting comparison point: A single CD can hold 700MB of data and a DVD can hold 4.7GB. Because the discs are relatively cheap, you could store data for a similar cost per GB compared to storing data on an HDD. 38 Table 1-5
Input and Output (I/O) Input : Creating information in computer 1. Typing at keyboard 2. Clicking with mouse 3. Talking into computer microphone 4. Recordings from video security camera connected to computer 5. Statistics gathered by website 6. Sales data from grocery store scans 39
Input and Output (I/O) Output: Presents information to users and for other purposes 1. Computer display showing image or some video 2. Computer speakers playing sound 3. Printers printing images 40
How Keyboards Send Bits to Represent Letters To physically send bits to the computer, the keyboard varies the electrical signal over time. From example, to send a binary 1, the keyboard might use a positive voltage (the current flows in one direction), and to send a 0, use a negative voltage (current flows in opposite direction). 41 Figure 1-20
How Keyboards Send Bits to Represent Letters (cont.) Imagine the user has opened a text editor and is ready to practice typing The quick brown fox jumped over the lazy river. The graphic here illustrates what happens when the T is pressed (requires 2 keys, the Shift and t keys). 42 Figure 1-21
How Keyboards Send Bits to Represent Letters Assuming uppercase T is pressed, here is how the current flows from each pressed key to the keyboard s processor: 43 Figure 1-22
How Keyboards Send Bits to Represent Letters Keyboard basically monitors for pressed keys and then reacts (notices which electrical circuits have a current). The processor determines which circuits have current, then the keyboard processor uses the keyboard map to decode the circuits, and then it sends the binary code for the character to the CPU. 44 Figure 1-22
45 The Mouse Allows control of computer s actions but in much different way than keyboard: Point-and-Click When user moves mouse pointer, OS has list of actions to take depending on mouse action 1. Single click of left mouse button causes OS application window to become active 2. Double click of left mouse button when pointing at icon or file causes OS to start application or open file 3. Single click of right mouse button causes app or OS to display contextual menu based on where pointer was when click occurred
Mechanical Mice and How They Sense Movement (cont.) The mouse essentially translates the movement in any direction into movement on an X,Y graph. The internal wheels have a 90 degree separation. The wheel aligned front-to-back measures movement in the Y-axis, and the wheel aligned side-to-side measures movement in the X-axis. 46 Figure 1-23
Coordinating Mouse and Mouse Pointer Movements To tell the computer to move the mouse pointer, the mouse sends bits to the CPU. The bits together make up a message, with some bits stating how much movement on the X-axis (and which direction), and other bits stating how much movement on the Y-axis, plus direction. 47 Figure 1-24
Other Mice Many vendors also sell wireless keyboard and mice combinations, which use a single receiver for both keyboard and mouse, as shown below. 48 Figure 1-25
Provides output The Computer Display Also called computer monitor or screen Shines light so user can see information on screen Sits outside system unit, connecting to system using cable When system powered off, display either shows nothing or some kind of error message 49
The Computer Display The OS decides what to display; sends information to the display adapter; and the display adapter sends the specific details about what lights and colors of lights to use on the display to make that image show up. When the application changes the contents of the window, the app stores some binary representation of that window in memory. The OS plays the role of managing the windows and updating the entire view of the desktop. 50 Figure 1-26
The Computer Display (cont.) Component Location (Internal/ External) Contributes to Making Image Display on Monitor OS Display adapter Internal Internal Creates desktop Works with app windows Directs display adapter Converts binary representation of screen to commands understandable and useful to display Display External Lights pixels with colors as specified by display adapter Apps Internal Create contents inside desktop window 51 Table 1-6
Pixel Grids and Pixel Maps (Frame Buffers) Imagine you are back in art class and the teacher gives you a piece of paper with a grid of squares on the right and open space on the left. Your art project for the day: draw a stick figure on the left, and then draw the same stick figure inside the grid. However, when drawing in the grid, you may only color 1 square at a time, filling it in completely. 52 Figure 1-27
Pixel Grids and Pixel Maps (Frame Buffers) Computer displays use grid of physical lights called pixels (short for picture element) Each pixel can shine light Maximum screen resolution defines number of pixels that physically exist on display 1. Resolution lists pixel width, then depth 2. Example1280 x 1024 resolution: Grid is 1280 pixels wide and 1024 pixels tall 53
Pixel Grids and Pixel Maps (Frame Buffers) OS and/or display adapter builds and updates pixel map (also called frame buffer) to control display 1. Lists whether each pixel should be lit or not, and what color it is 2. Represents each pixel as bit (1=on, 0=off) 3. If map set 1 bit per pixel, has enough information to tell display what to do for each pixel 54
Pixel Grids and Pixel Maps (Frame Buffers) Memory required for pixel map 1. Monitor is square with screen resolution of 1000 x 1000 2. Matching pixel grid also 1000 x 1000 (creating 1,000,000 total pixels) 3. 1 bit per pixel = 1,000,000 bits 4. 8 bits per byte = 125,000 bytes (125 KB) NOTE: Displays that have only one color called monochrome displays 55
Pixel Grids and Pixel Maps (Frame Buffers) (cont.) Most displays support color that use pixels that can shine light in large variety of colors Example: To support 8 colors per pixel requires 3 bits per pixel (2 3 unique numbers) To support 256 colors, need 8 bits (1 byte=2 8 ) Typical displays today use 24 bits (3 bytes=2 24 ) or 32 bits (4=2 32 ) for colors NOTE: 24 and 32 bits creates 16 million and 4 billion (or so) colors, respectively. This granularity is needed because the human eye can distinguish very fine shades of color. Test yourself by looking at color settings with any office application. Even with 1 bit changed in a 24-bit color code, side-by-side, you can tell the two color settings apart. 56
Printers Convert computer file to image on paper Uses method similar in concept to how display uses pixel map to create image on screen Uses number of dots on paper organized into grid Printers identified by how many dots per inch (DPI) they print in a square inch 1. More dots per inch = Better print quality 57
Printers Computer has to translate from its file to mapping of dots to print 1. Example: Word processor has bytes that represent The quick brown fox jumps over the lazy river. as ASCII stored in RAM 2. To print, printer driver translates bytes to correct format to determine which dots to print on paper to form each letter 58
Summary: This Chapter Defined concepts behind bits and bytes Described in general terms how computers store data in Random Access Memory (RAM) Explained how computers represent text characters using bits held in RAM Discussed how computer file systems organize data 59
Summary: This Chapter Described in general terms how computers store data on drives Explained general steps that occur when a key is pressed on keyboard Described the basic information that a mouse sends to a computer to move the mouse pointer Explained the concepts behind a computer display s pixel map, and how computers use bits to represent pixel color 60
Questions? Comments? 61