Chapter 1 computer: a device that accepts input, processes data, stores data, and produces output. Draw a picture of computer input central processor output device main memory 16 Megabytes secondary memory fixed disk 1 Gigabyte floppy disk 1.4 Megabyte accepts input: words and symbols in a document, numbers for a calculation, pictorial input, audion signals from a microphone, mouse clicks from a mouse, instructions for a process: input devices: keyboard, mouse, scanner, digitizer tablet, microphone (speech input), bar code scanner processing of raw data done by central processor (CPU): electronic circuitry in form of computer chips. Performs arithmetic operations (add, multiply, subtract, divide) at incredible speeds 109 operations per second. Also, performs comparisons of two numbers stored in memory (which is larger, which is smaller, are they equal). Based on these comparisons, CPU chooses from among alternatives and decides whether to continue a repetetive operation or to stop. Computer stores data in memory (main and secondary). kinds of data stored: any of the input data we mentioned earlier. Normally the instructions for a process are stored as well as the raw data to use in the processing. -- Stored program computer/Von Neumman computer. Each memory cell has unique address (fixed) but its contents can change (memory is volatile). Main memory directly accessible by the central processor - secondary memory is not. All data and instructions must be moved into main memory to be processed. Main memory is limited in size - up to 32 Megabytes for many computers. Seconday memory is not limited. Can be expanded almost indefinitely by removable storage media - disks, tapes, CD ROMs. Main memory is not permanent memory - contents disappears when computer is turned off. Secondary memory (storage in book) is semi- permanent - data stays on disk until you erase it. Bring a couple of disks to class - floppy disks 3.5 inches - IBM formatted - high density - 1.44 Megabytes ouptut devices - screen, printer, plotting device - draws graphs, maps, etc. To compute a water bill: step 0. Assume a program has been written and stored in computer memory as a list of instructions. The computer begins to execute the program instructions, which cause the following sequence of operations to occur: 1. Computer reads data (number of gallons used, category of user - industrial, home) entered at keyboard into memory. 2. Computer finds appropriate rate/gallon for the amount and category of user using decision-making capability of CPU. 3. Computer calculates charge using arithmetic capability of CPU. 4. Computer prints a bill for customer using printer. A program is a software product which enables the computer to perform a particular task. Without software, a computer is useless. Examples of software: programs that play games, programs that help you prepare resumes, programs that compute payroll for a business, programs that help you learn a foreign language, etc. More on software later!!! Kinds of computers: microcomputers, personal computers, PCs - cost around $2000, found in homes and small businesses. Accomodates one user at a time - may be connected to other computers. IBM compatibles and Macinstoshes are the two kinds of microcomputers widely available. workstation - largest kind of microcomputer. Used for doing computer- aided design and other engineering/scientific operations that require extensive computation. Faster than smaller microcomputers. Costs from $5000 - 10,000. Minicomputers - slightly larger than microcomputers. A single minicomputer can accomodate several users (up to 100). Each user has a terminal connected to miniciomputer - terminal is a keyboard and screen. Terminal transmits your processing requests to the minicomputer. Minicomputer sends results back to terminal after processing is complete (sometimes called dumb terminals). The operating system has to allocate system resources among its many users so that each user is not kept waiting an inordinate amount of time. May cost from $10,000 up to $100,000. Mainframe computers are large, fast, expensive. Used by major corporations for centralized storage, processing, and data management. Temple University uses a mainframe comptuer to handle on- line registration, for payroll, for printing end-of-semester grade reports. A mainframe computer may handle many operations and accomocate many users (200 or more) simulateneously and will have multiple processing units. Will cost several hundred thousand dollars. Supercomputer - largest mainframe. For performing extremely sophisticated calculations in minutes which might take hours on smaller mainframes- nuclear modeling, weather prediction. Usually used by a few people at a time rather than hundreds. May cost several million. Compatible computers are computers that can run the same software. IBM compatible are the most visible kinds of compatible computers. All run the microsoft operating systems and same software. Computers may be made by IBM, Gateway, compaq, Dell, to name a few. computer network: collection of computers and other devices (disks, printers) connected to share data, hardware, and software. Different kinds of computers can be connected on a network (micros, minis, mainframes). Network users can send messages to each other and access data on a central storage device. They can send files to a central printer to be printed. There are local area networks (a computer laboratory, the computers in a single office) and wide area networks. The internet is a wide area network and can be accessed by users all over the world. Security is of concern on a network because the network managers want to keep unauthorized users out. Each user must log in to access a network: To log in, you must provide when requested: Your user-id (given to you be the network adminstrator) and your password (initial password given to you - you personalize it). User log in screen: User id ________________ | | ------------------- Password ________________ | | ------------------ You should try to pick a password that is not easy for someone who knows you to figure out: Bad passwords: birthdays, hobbies, boyfriend or girlfriend name, dog's name, car name, etc. User interface: a combination of hardware and software that enables humans to communicate with computers. Hardware consists of items like a mouse, keyboard, light pen, touch-sensitive screen. The software is the program that controls the interaction. Least sophisticated user-interface: Sequence of prompts displayed - user repsonds to each prompt and computer interprets user response - types "try again" or "please redo" if it can't understand user repsonse. Old operating system for IBM computers (called MS-DOS) produced this sequence of unintelligible prompts: Enter date XX-XX-XX> Enter time: XX:XX:XX> C:> User should respond: 9-5-96 (sept. 5 1996) 10:21 (10:21 AM) wp50 (run word perfect version 5.0) In MS-DOS, once you got the system prompt C:> (indicates operating system is waiting for your instruction), you would type in a COMMAND C:> DIR - list my files C:> copy resume.ebk oldrsume.ebk - make a duplicate copy of a file under a different name. c:> WP50 run word perfect word processor program C:>A: change to disk drive A (a floppy disk - C is the hard disk) Command line interface - an interface which requires the user to type in commands. Menus - second kind of user interface. Common menus are pull-down menus, which means you make a selection and can pull down a list of sub-menus associated with that selection or cause an action to occur if there is no sub-menu for that selection. Example: Word word processor program File Edit View Insert .... Menu choices above, select one by pointing mouse and holding down mouse button and you get a sub-menu under that selection. YOU keep mouse button depressed, move mouse to a new choice in that sub-menu, and then release button to select it. Edit Undo Typing Repeat typing Cut (not available) Copy (not available) Select All Find ... Replace ... Goto ... The gray choices are not currently availabe. The bold choices are. If you select one ending in ... you get a dialog box to fill in with further information: for Goto - you see this box: (draw rectangle around it) go to page number OK buttons with circles around them __________ Cancel |XXXXXXXX| ------------ Cursor is placed inside box that is filled in with solid bar. Type the number fo the page you wish to advance to. To advance, move cursor to OK button and click on it. Graphical User Interfaces (GUIs) Interface used with Macintosh and windows operating systems: Collection of graphical objects displayed on the screen. You can manipulate them using a mouse. Each graphical object represents a computer task, command, or an object or file. Graphical objects include: icons (small pictures), buttons, tools, and windows. icon for microsoft word: --------= |-----\ |Word\ |------\ Move mouse to it, and click twice to select the word program. The icon is highlighted in color when you select it. You can have several windows open on your screen at one time. Each window represents a specific task that is ongoing. YOu might have a window open for a document your are creating. If you have several windows open, you can switch between them - allows you to work on several different tasks at same time. Window for word: Document: CIS10class1 File Edit .... (pull down menu) file folder button disk button printer button Times new roman 12 _________________________________ | Graphical User Interfaces (GUIs) Interface used with .... |