K Hinds Page - 1 Lecture 2

Transcription

1 Page - 1 Lecture 2 CSEC Information and Communication Technology Lecture 1 Continued Storage Device Terms Continued: Buffers & Cylinders A Buffer is a temporary memory location that is used to store data as it is being moved from one point to another. A Cylinder is any set of all of tracks of equal diameter in a hard disk drive (HDD). It can be visualized as a single, imaginary, circle that cuts through all of the platters (and both sides of each platter) in the drive. Hard Disk Drive Terms: Access Time, Sequential Access and Direct Access The Access Time refers to the time that has lapsed between a request for data and a response from the HDD with the data. Sequential Access is a method of accessing data on a memory device. Sequential accessed mediums must have their tracks scanned one by one to until the reading mechanism reaches the correct position for the requested information and is then able to read it. An examples of this is a Magnetic Tape Direct Access is also referred to as Random Access as it allows data to be retrieved immediately at some specific location on the storage media without scanning progressively from the beginning of the data store on each read request. Device interfaces: SCSI Small Computer System Interface (SCSI) [pronounced as Skuzzy ]. These external interfaces are used to connect peripherals to the computer for expanded utilization of the computer and its resources. Some examples of SCSI connectors are given below: Integrated Drive Electronics (IDE) is an interface for connecting optical and hard drives to a computer motherboard. This interface supports a 40 pin connecter. IDE technology is also referred to as PATA (Parallel ATA).

2 Page - 2 Lecture 2 Serial ATA (SATA) is based on the IDE technology infrastructure. However this connection is a lot simpler in construction, operation and magnitude. Input Devices and Media Webcam Mouse Joystick Keyboard Digital Camera Document Scanner Remote Control Pointing Devices Tablets Optical mark reader (OMR) Optical Character Reader/Magnetic Ink Character Reader (OCR, MICR) This is a visual device that captures the video of the user of the computer. This is a device used by the user to select options and navigate items visually on the computer screen This is a device used with graphical software to capture analogous user input This device is used to capture text and numerical data from the user This device is used to capture photographs and transfer them to the computer This is a device used to make digital copies of physical documents. The Document Scanner scans the document using a photo sensitive cover plate and a high intensity light source. This is a small portable device used to control the computer through a Bluetooth, wireless or infrared controller. These devices are used in conjunction with a computer to allow the user to select various items on a screen by pointing the pen at various objects on a screen or onto a device. The pen emits a beam of light that is shone onto objects to read barcodes or onto a light sensitive screen to capture user input. These are touch sensitive devices that are portable and convenient for users to use daily. A tablet can offer an ease of convenience where traditional laptop or desktop computers may be too bulky to use. An OMR is a scanning device used to capture input from cards and other predefined documents. The OMR scans the document and checks for a difference in density of marks on the page at various locations and compares it to a master file for processing. Multiple choice questionnaires are usually corrected with OMR s. These devices scans documents and gives a digital editable copy of the same document, thereby eliminating the need to retype the entire document.

3 Page - 3 Lecture 2 Point of Sale (POS) This is a complete system found in supermarkets and other retail environments which includes devices captures the transaction using a variety of devices which include computers, cash registers, optical and bar code scanners, magnetic card readers, or any combination of these devices. Biometric Systems These systems uses biological information from the user to access some service with a computer. Biometric devices include eye scanners, finger print readers and voice recognition.

4 Page - 4 Lecture 2 Lecture 2 Visual Display Units A VDU displays images generated by a computer or other electronic device. The term VDU is often used synonymously with "monitor," but it can also refer to another type of display, such as a digital projector. Visual display units may be peripheral devices or may be integrated with the other components. VDU sizes are measured diagonally from one end of the screen to the next. Cathode Ray Tube (CRT s) The image on a CRT display is created by firing electrons from the back of the tube to phosphors located towards the front of the display. Once the electrons hit the phosphors, they light up and are projected on the screen. The color you see on the screen is produced by a blend of red, blue, and green light, often referred to as RGB. The stream of electrons is guiding by magnetic charges, which is why you may get interference with unshielded speakers or other magnetic devices that are placed close to a CRT monitor. CRT s are usually small in size since the electron gun needs to be further from the screen to produce a larger image on larger screens. Therefore larger screens need lots of room and can become bulky. Flat Screen (Plasma, LCD, LED) A Plasma display illuminates tiny, colored fluorescent lights to form an image. Each pixel is made up of three fluorescent lights -- a red light, a green light and a blue light. Just like a CRT television, the plasma display varies the intensities of the different lights to produce a full range of colors. Plasma screens work by exciting tiny pockets of gas (Xenon and Neon), changing them to a plasma state. In that state, the electrons of that gas emit ultraviolet light, which is not visible to the human eye. The ultraviolet light is then absorbed and re-emitted into the visible spectrum of light by the phosphor inside each cell. Each pixel consists of three sub pixels: one red, one blue, and one green. The more excited the gas, the brighter the color produced. The pixel is not excited continuously, but in short pulses. The naked eye perceives this as flickering. Some people are very sensitive to this. The effect is reduced on higher-end models because the flickering is a lot faster. Because each pixel emits its own light, the blacks are really deep. When the television wants to display black, it simply emits no light at all for the selected pixels. Plasmas suffer from occasional image retention if they display the same image for a very long period of time. LCD Stands for "Liquid Crystal Display." LCDs are super-thin displays that are used in laptop computer screens and flat panel monitors. Smaller LCDs are used in handheld TVs, PDAs, and portable video game devices. The screen is composed of two parts: the actual liquid crystal display and a light source at the back of the screen (called backlight). A light diffuser is placed between the backlight and the LCD screen to make the source of light uniform across the screen. The LCD screen does not emit light by itself; it only acts as a filter to block the light on a per pixel basis. The opacity of a pixel can be controlled by applying an electric field to it. If the screen wants to display black, the LCD pixel will try to block the light completely. If it wants to display white, it will let it through. Because the display is only a filter, the blacks will not be as deep as with a plasma screen. An LCD pixel, even if it displays black, will always let through a small portion of the light. An LED screen is actually an LCD screen that uses light-emitting diodes (LEDs) as a source of light behind the screen. An LED is more energy efficient and a lot smaller than the lighting mechanism used in a LCD screen, enabling a thinner television screen. Since it is only the backlight that changed, there is actually no picture quality improvement over a normal LCD screen.

5 Page - 5 Lecture 2 Printers A printer is a device that produces a physical copy of text and graphics on the computer screen. Printers need supplies to work, which is referred to as consumables. These include standard sizes of paper and ink. Printers come in many sizes and operating functionalities. Impact and Non-Impact Printers Impact printers include all printers that work by striking an ink ribbon. Daisy-wheel, dot-matrix, and line printers are impact printers. Daisy-wheel: Similar to a ball-head typewriter, this type of printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper. Daisy-wheel printers produce letter-quality print but cannot print graphics. Dot-Matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations. Non-impact printers do not strike any ink ribbons and as such are usually quieter than their impact counterparts. Ink-Jet: Sprays ink at a sheet of paper. Ink-jet printers produce high-quality text and graphics. Ink-Jets prints letter by letter. Line Printer: Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low-quality print. Laser: Laser printers produce very high quality text and graphics. It does this by printing page by page which take less time to print the overall document that an ink-jet would. LED: These are non-impact but use a light-emitting diode instead of a laser in the print head. LED printers function by focusing light across the entire length of the drum, thus creating areas that are less charged, which attracts toner. The printer then transfers the toner from the drum to the paper and applies intense heat to fuse the toner to the paper. Thermal Printer: An inexpensive printer that works by pushing heated pins against heatsensitive paper. Thermal printers are widely used in calculators and fax machines. Plotters: A plotter is used for printing vector graphics. Instead of toner, plotters use a pen, pencil, marker, or another writing tool to draw multiple, continuous lines onto paper rather than a series of dots like a traditional printer. Plotters are used to produce a hard copy of schematics and other similar applications. Printers are also classified in terms of physical characteristics. These are speed, quality, storage and capacity. Quality: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Speed: Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute. Storage: Most printers today come equipped with their own memory and they can be shared over a network. The size of a laser's memory is measured in megabytes (MB), and ranges from 2MB to 128 MB. The more megabytes, the faster the laser can process multiple print jobs and the faster it can print each page. Capacity: A printer's input capacity measures the number of sheets of paper the printer can hold for printing, while the output capacity describes the number of printed pages it can accommodate before needing to be cleared. Depending on the printer model, input capacity ranges from 150 to 1100 pages, and output capacity from 100 to 600 pages.

6 Page - 6 Lecture 2 Speakers Audio output devices A hardware device connected to a computer's sound card that outputs sound generated by the computer. Head-Phones/Earphones Sometimes referred to as earphones, headphones are a hardware device that either plugs into your computer (line out) or your speakers to privately listen to audio without disturbing anyone else. Data & Information Other Computing Terms Data are raw facts and figures. Information is the summarization of data. Technically, data are raw facts and figures that are processed into information, such as summaries and totals. Microfilm Microfilming, also called microphotography, consists in the reduction of images, books, newspapers and other printed materials to such a small size that they cannot be read without optical assistance. This amazing photographic compression often results in a ninety-nine percent saving of space. The microfilming service is one of the most extensively used and common practices in modern reprographic science. Hard Copy & Soft Copy A Hard Copy (or "Hardcopy") is a printed copy of information from a computer. Sometimes referred to as a printout, a hard copy is so-called because it exists as a physical object on paper. The same information, viewed on a computer display or sent as an attachment, is sometimes referred to as a soft copy. Human Readable & Machine Readable The Human Readable formats have the advantage of being easily understood by a person reading them as they are typed in a standard language. Machine readable formats are written in code that allows the computer to easily read and interpret the instructions.

7 Page - 7 Lecture 2 Binary - Counting Numbering Systems Binary describes a numbering scheme in which there are only two possible values for each digit: 0 and 1. The 0 and 1 values are sometimes called "low" and "high," or ON and OFF respectively. Decimal Binary (using 4 bits) Binary to Decimal Binary numbers have a positional weighting starting small from the right hand side and moving leftwards to the greater weightings on the left hand side. Above we examined Binary on 4 bits, but a standard byte consists of eight (8) bits. Below we look at the representation of a byte. HIGHEST VALUE SMALLEST VALUE As you can see above, depending on where a 1 lies within a byte, that determines the value of the byte. For example, let us try to figure out the value of the byte given below:

8 Page - 8 Lecture 2 From above, we see that the only bits that have a 1 are the 2 nd and 4 th bits. Therefore the above byte is a representation of the number? 2 nd bit weight = 2 4 th bit weight = 8 Therefore = 10. Hence the binary number above is the decimal number 10 equivalent. Let us try to deduce the following values of bytes: Were you able to deduce the Decimal equivalent of the bytes given above? FANTASTIC! Now that we know how to count in Binary and we also know how to convert Binary to Decimal Let us look at converting Decimal to Binary. Decimal to Binary To convert Decimal to Binary, we simply devide any number we have by 2 and record the remainder in a separate row. Once done, we can then provide the resultant in binary. Lets look below and see: a) Convert the Decimal number 25 into Binary: Answer: 25/2 = 12 R 1 12/2 = 06 R 0 06/2 = 03 R 0 We write the answer with the top numbers first, but in the order 03/2 = 01 R 1 right to left: /2 = 00 R 1 Notice that above we only have 5 bits, but a Byte is represented with eight bits. Therefore we add the remaining Zero s to make up the byte: That s it! Now we can write any decimal number into its binary equivalent. As practice, can you convert 189, 255, 109, 87 and 300 into binary?

9 Page - 9 Lecture 2 Binary Addition Addition in Binary begins by understanding how to add in Binary = = = = = 11 Note that the 1 is the carry bit that goes to the leftmost bit For Example: Add the following binary numbers: Try it and see if you get what I have below Binary Subtraction Subtraction begins by understanding the basic rules in Binary subtraction: 0 0 = = ERROR-Must borrow from the left/leftmost bit 1 0 = = = = 10 For example: Subtract the following binary numbers: Try it and see if you get what I have below

10 Page - 10 Lecture 2 Binary Sign and Magnitude Negative numbers are essential, and any computer not capable of dealing with them would not be particularly useful. But how can such numbers be represented? There are several methods which can be used to represent negative numbers in Binary. One of them is called the Sign- Magnitude Method. The Sign-Magnitude Method is quite easy to understand. In fact, it is simply an ordinary binary number with one extra digit placed in front to represent the sign. If this extra digit is a '1', it means that the rest of the digits represent a negative number. However if the same set of digits are used but the extra digit is a '0', it means that the number is a positive one. The following examples explain the Sign-Magnitude method better. Let us assume that we have an 8-bit register. This means that we have 7 bits which represent a number and the other bit to represent the sign of the number (the Sign Bit). This is how numbers are represented: The red digit means that the number is positive. The rest of the digits represent 37. Thus, the above number in sign-magnitude representation, means +37. And this is how -37 is represented: Exercise: 1. Write '-93' in sign-magnitude representation, using an 8-bit register. Did you get ? 2. What is the largest positive number which can be represented in an 8-bit register, using the sign-magnitude method of representation? [ ] =? 3. What is the largest negative number which can be represented in an 8-bit register, using the sign-magnitude method of representation? [ ] =? 4. Give the range of possible numbers which can be represented in a 16-bit register, using the sign-magnitude method. ( to ) Binary - Binary Coded Decimal (BCD) Binary coded decimal (BCD) is a system of writing numerals that assigns a four-digit binary code to each digit 0 through 9 in a decimal (base-10) numeral. The four-bit BCD code for any particular single base-10 digit is its representation in binary notation, as follows:

11 Page - 11 Lecture 2 Numbers larger than 9, having two or more digits in the decimal system, are expressed digit by digit. For example, the BCD rendition of the base-10 number 1895 is The binary equivalents of 1, 8, 9, and 5, always in a four-digit format, go from left to right = The BCD representation of a number is not the same, in general, as its simple binary representation. In binary form, for example, the decimal quantity 1895 appears as = NOT BCD Other bit patterns are sometimes used in BCD format to represent special characters relevant to a particular system, such as sign (positive or negative), error condition, or overflow condition. The BCD system offers relative ease of conversion between machine-readable and humanreadable numerals. As compared to the simple binary system, however, BCD increases the circuit complexity. The BCD system is not as widely used today as it was a few decades ago, although some systems still employ BCD in financial applications. Binary - Two s Compliment For positive numbers in two s compliment, we represent them in their binary equivalent. However negative numbers are handled slightly differently. We first invert every bit of the number and then add one (1) to the result. For example, let us write -56 in two s compliment: We write +56 first To get two s compliment, invert all bits + 1 Add one Two s compliment representation of -56