Lesson Script - How Computers Work

How Computers Work

Objectives

Materials Required:

Hardware

Discussion Topics

Components Used Primarily for Processing

Temporary (Primary) Storage Devices

Permanent (Secondary) Storage Devices

Discussion Topics

Describe the difference between hardware, software and firmware. Example: Hardware includes the physical devices that makeup a computer. Software includes programs that tell the computer how to use these devices. Firmware is program code that is permanently stored on a chip that often serves as a “middle man” between hardware and software.

Define peripheral devices and ports. Example: The monitor, keyboard, and mouse are peripheral devices. Ports are used to connect the peripheral devices to the system (i.e., COM1, or LPT 1).

Demonstrate that some connectors may look similar and have different purposes, such as the keyboard and mouse connectors.

Define pixel. Example: A pixel is a dot or unit of color that is the smallest unit of display on a monitor.

Define device driver. Example: A device driver converts data from a language an application can understand into a language the hardware can understand.

Define CMOS. Example: CMOS is a chip that can maintain configuration information as long as it has an electrical charge. It is used on system boards to remember hardware configuration information such as the presence of a hard drive, floppy drive or CD-ROM drive.

Discuss the purpose and design of expansion cards. Example: Expansion cards were originally created to modularize the installation of additional hardware such as video cards, sound cards and I/O cards.

Briefly demonstrate the difference between a data ribbon cable and a power connector.

Briefly discuss the role of a CPU. Example: The CPU is the heart of a PC, it is involved in almost every calculation the PC makes.

Define bus. Example: There are thousands of little circuits between chips on a system board. The combination of these circuits and the language they use to communicate is referred to as the bus.

Components Used Primarily for Processing

Define chipset. Example: A group of chips on the system board that relieves the CPU of some of the system’s processing tasks, increasing the overall speed and performance of the system.

Define coprocessor. Example: A chip or portion of the CPU that helps the microprocessor perform calculations and speeds up computations and data manipulations dramatically.

Temporary (Primary) Storage Devices

Define Primary storage. Example: Temporary storage on the system board used by the CPU to process data and instructions.

Define RAM and its function. Example: RAM is a type of memory chip that temporarily stores data until the CPU asks for it or the power is cycled. It is also sometimes referred to as primary storage.

Discuss how RAM chips are installed. Example: RAM chips are most commonly installed on a mini circuit board that plugs into the system board. SIMM’s and DIMM’s are examples of these circuit boards.

Define Cache memory. Example: Cache is a kind of fast RAM that serves as a holding area for data that is accessed frequently. It is more efficient that volatile RAM because it does not need to be continually refreshed.

Mention that traditional Cache memory comes as individual chips situated on the system board. Newer Cache is often stored in a chip inside the CPU package. Some systems use an insertable card called a COAST module to support upgrade ability. The COAST module was unpopular due in part to few, if any, users upgrading, and reliability issues.

Permanent (Secondary) Storage Devices

Define secondary storage. Example: Remembering that RAM is considered primary storage, secondary storage is everything else. Examples include floppies, hard drives and CD-ROMs.

Describe the internal workings of a hard drive. Example: A hard drive consists of several metal platters and metal read/write heads. The heads move over the platters to read and write data. In some cases, the platters may be made of a hardened glass.

Mention that if hard drive heads ever touch the platters, it is considered a head crash. Bumping or dropping a hard drive could cause a head crash. Note that because laptops are portable they are more susceptible to hard drive crashes.

Mention older hard drives had a feature called “parking” that retracted the read/write heads to a “safe” position. All newer hard drives perform the “parking” function when powering down.

Define hard drive controller. Example: A hard drive controller is the device responsible for directly controlling the head movement of the hard drive. Mention that older hard drives did not come with onboard controllers.

Mention that very old hard drives had separate cables for power, data, and controller/system commands. The data/system cable solution was very unreliable. Today, data and controller/system commands are carried on ribbon cables. Loose or improperly seated cables are still a considerable problem.

Describe floppy drives. Example: A floppy disk uses the same concepts as a hard drive but because it is designed to be portable it doesn’t have any heads and has only one platter, which is made of plastic. In order to read the data stored on a floppy disk, the disk must be put into a floppy drive. The drive then uses its heads to read the data stored on the floppy disk’s platter.

Mention that students may begin to notice that floppy disks have remained quite unchanged for many years with few significant changes. Discuss the care of floppy disk media, if students will use floppy disks in coursework.

Define Trace. Example: A wire on a circuit board that connects two components or devices together.

Define protocol. Example: A protocol is a set of rules and standards that any two entities use for communication.

Define system clock. Example: A line on a bus that is dedicated to timing the activities of components connected to it. The system clock provides a continuous pulse that other devices use to time themselves.

Mention that in computer parlance, terminate means “connect” to. It usually means the end of a circuit, but may be an intermediate junction.

· PCI (Peripheral component interconnect) expansion slot used for high-speed input/output devices.

· ISA (Industry Standard Architecture) expansion slot used by older and/or slower devices.

Describe how to identify different types of expansion cards. Use the demonstration workstation to show the differences between the two cards. Note to students both the end of the expansion card and the bus type of the expansion card.

Point out a modem or multiple interface network card to demonstrate that some cards can connect in a variety of ways.

Describe the function of a power supply. Example: The main purpose of a power supply is to convert electricity from 110AC to either 5 or 12 volts for the system board and other devices.

Mention to students that standard PC power supplies have two connectors for the system board, one for floppy drives and four connectors for devices like hard drives and CD-ROMs, although these vary from vendor to vendor.

Mention that some power supplies have a switch to alter input wall voltage from US 115-120V to Europe 215-220V.

Define BIOS. Example: BIOS (Basic input/output system) is firmware that controls much of a computer’s input/output functions, such as communication with the floppy drive, RAM chips, and the monitor. Also called RAM BIOS.

Describe Flash ROM. Example: ROM is an example of hardware, it is a chip that can hold data without an electrical charge. Flash ROM is an example of firmware. It can also hold data without an electrical charge, but unlike ROM the data can be erased and rewritten by software.

Discussion Topics

Explain the purpose of BIOS and device drivers. Example: The purpose of the BIOS is the same as the purpose of device drivers, which is to translate software instructions into a language that the hardware components can understand.

Define the system BIOS. Example: The system BIOS is a combination of all of your computer’s different BIOS’s combined. These BIOS’s would include the video BIOS, the startup BIOS, and any others that may be installed.

Define device driver. Example: A small program stored on the hard drive that tells the computer how to communicate with an input/output device such as a printer or modem.

Briefly summarize what happens when a command is executed within an operating system:

· The operating system translates and forwards that request to the BIOS or proper device driver.

· The BIOS or device driver translates the request into the specific electrical pulses that the hardware device can understand.

(Optional) Note that sometimes the operating system sends requests to DOS and then DOS sends those requests to the BIOS or device driver. This depends on the operating system.

Define memory address. Example: A number assigned to each byte in RAM. The CPU can use memory addresses to track where information is stored in RAM. Memory addresses are usually displayed as hexadecimal numbers in segment/offset form.

Mention that the segment/offset form is used liberally in the field and must be understood. A brief demonstration in class may be in order. Pick a few students in a row of seats. Write their names on the board in a list. Tell the students you need a simple “instruction” that tells a person to deliver a handout or item to each.

If you have picked five students, the instruction should be similar to this: <first student name> plus next four.

Now mention that the CPU and operating system can use this form to perform memory functions using a minimum of information. The program counter register names the first address location and some other register can provide the offset, instead of a huge register that must hold a list of up to all possible addresses.

Define operating system. Example: The operating system creates an environment in which all applications can be executed.

Briefly list some of the most common operating systems and note that the operating system is normally stored on the hard drive. Example: DOS (Disk Operating System), Window 3.1, Windows 95, Window NT, OS/2 and UNIX.

Define file. Example: A collection of related records or lines that can be written to disk and assigned a name (for example, a simple letter or a payroll file containing data about employees).

Define program file. Example: A file that contains instructions designed to be executed by the CPU.

Briefly describe the boot process, focusing on the operating system. Example: When a system is booted, it reads the boot record of its primary hard drive and looks for an operating system. If it finds one, it copies the necessary files into RAM and loads the operating system.

Describe the computer process involved when an application is executed. Example: After the first set of program instructions is copied to RAM the instructions are executed by the CPU. This set points the CPU to another set of instructions stored at a different location within the RAM. The CPU then executes those instructions.

Discuss the two types of operating system interfaces (command line and menu-driven).

Define GUI (Graphical User Interface). Example: Any interface that uses icons and graphics to communicate with the user. Windows is an example of GUI.

Define multitasking. Example: Multitasking refers to the ability to execute more than one task at a time. Mention that older CPUs and operating systems did not have this ability.

Define cooperative multitasking. Example: A type of pseudo-multitasking whereby the CPU switches back and forth between programs loaded at the same time. One program sits in the background waiting for the other to relinquish control. Also called task switching.

Define preemptive multitasking. Example: A type of pseudomultitasking whereby the CPU allows an application a specified period of time and then preempts the processing to give time to another application.

Discuss the difference between cooperative multitasking and preemptive multitasking.

Mention that in the Windows 3.x environment, Windows sometimes relies on DOS to act as the middleman between the operating system and the BIOS or device driver.

Define environment. Example: The environment refers to the operating system and its capabilities, it is what the user experiences, it is situational, what the user sees, hears, and experiences while performing tasks.

Describe how DOS, Windows 3.1 and Windows 95 handle multitasking. Example: DOS does not multitask at all. Windows 3.1 simulates multitasking by passing tasks to the CPU one at a time. Windows 95 was the first PC operating system to use true multitasking features.

Ask the students to evaluate and compare different operating systems such as Windows 95, Windows 98, UNIX, NT, Windows 2000, Macintosh, and Windows3.1. Use the tables on textbook pages 35 – 40 for reference. Use questions like:

Describe what a file is and the DOS naming convention. Example: A file is a collection of data stored under one name on any secondary storage device. When using the DOS operating system a file name is limited to eight characters.

Describe file extension and what it is used for. Example: A file extension is the last three characters of a file name after the period. DOS uses the file extension to recognize what type of data is stored within a specific file.

Describe the difference between long file names and DOS file names. Example: Long file names can contain up to 256 characters, rather than the eight –character limitation of DOS.

Define real mode. Example: A single-tasking operating mode whereby a program only has 1024K of memory address, has direct access to RAM, and uses a 16-bit data path.

Define protected mode. Example: An operating mode that supports multitasking whereby the OS manages memory, programs have more than 1024K of memory addresses, and programs can use a 32-bit data path.

Define virtual memory. Example: A method whereby the OS uses the hard drive as though it were RAM.

List the six types of applications and describe what they are used for (i.e., word processing, spreadsheets, database management, graphics, communications and games).

Define suite. Example: Suites are sets of programs that are designed to be compatible with each other. Suites normally include enough applications to encompass 5 out of the six types of applications previously listed.

Mention that applications are normally designed with a specific operating system in mind.

Define directory. Example: A directory is a folder where files can be stored.

Discuss the difference between the root directory and subdirectories. Example: Think of the root directory as the main folder. All files and folders on the PC are ultimately stored in the main folder, or root directory. Note that the root directory is represented by a backslash.

Explain how to execute a DOS file and discuss what DOS does in the background. Example: To execute a file under DOS, type in the name of the file. DOS will then search for the file in the following order: .com, .exe, .bat. Note also that DOS will only search the current directory unless a search path has been specified.

Define search path. Example: The search path is the default directories that DOS will search when looking for an executable. The search path can be edited using the PATH command or by modifying the AUTOEXEC.BAT.

Mention that if you specify a path when attempting to execute a file, DOS will not have to search for the file.

Describe how a short cut works behind the scenes. Example: In the Windows environment, command lines are assigned to short cuts to make it more user- friendly.

Windows 95 uses command lines for its icons, and those command lines can still be viewed via the “properties” option. Demonstrate this by right clicking a “Short cut” and picking properties.

Troubleshooting Windows. The key thing to remember when troubleshooting in the Windows environment is to follow the process. Example:

· Verify that the hardware component involved is functioning properly. For example, if there were a printing problem, you would run a self-test on the printer.

· Verify that the hardware involved is communicating with the BIOS or device driver. Verify that the correct device driver is being used.

Explain that Windows NT has a similar interface to Windows95. Example: Windows NT still uses command lines for its icons, and those properties can still be viewed via the properties option in the file menu. Explain that the underlying program code is significantly different and is based upon architecture designed to be more “adaptive.”

Explain that Windows 2000 has a similar interface to Windows95 and Windows NT. Example: Windows 2000 still uses command lines for its icons, and those properties can still be viewed via the properties option in the file menu. Its underlying architecture is based upon Windows NT, not Windows95.

Explain that UNIX has a different interface that is somewhat similar to DOS, but is completely different. UNIX is known for its cryptic names for many functions. It comes in numerous forms from shareware sources to very expensive, commercial varieties. UNIX may be difficult to use with many hardware platforms and care should be taken when selecting a version for home or commercial use.

Backward compatible — Refers to new hardware and software that is able to support older, existing technologies. This is a common choice of hardware and software manufacturers.

Binary number system — The number system used by computers; it has only two numbers, 0 and 1, called binary digits, or bits.

BIOS (basic input/output system) — Firmware that controls much of a computer’s input/output functions, such as communication with the floppy drive, RAM chips, and the monitor. Also called RAM BIOS.

Booting — The process that a computer goes through when it is first turned on to get the computer ready to receive commands.

Bus — The paths, or lines, on the system board on which data, instructions, and electrical power travel.

Cache memory — A kind of fast RAM that is used to speed up memory access because it does not need to be continuously refreshed.

Cards — Adapter boards or interface cards placed into expansion slots to expand the functions of a computer, allowing it to communicate with external devices such as monitors or speakers.

Chip set — A group of chips on the system board that relieves the CPU of some of the system’s processing tasks, increasing the overall speed and performance of the system.

Circuit boards — Computer components, such as the main system board or an adapter board, that have electronic circuits and chips.

Client — A computer that is connected to another computer and uses programs and/or data stored on the other computer.

CMOS (complementary metal-oxide semiconductor) — One of two types of technologies used to manufacture microchips (the other type is TTL, or transistor-transistor logic chips). CMOS chips require less electricity, hold data longer after the electricity is turned off, are slower, and produce less heat than do TTL chips. The configuration or setup chip is a CMOS chip.

COAST (cache on a stick) — Memory modules that hold memory used as a memory cache. See Cache memory.

Cooperative multitasking — A type of pseudomultitasking whereby the CPU switches back and forth between programs loaded at the same time. One program sits in the background waiting for the other to relinquish control. Also called task switching.

Coprocessor — A chip or portion of the CPU that helps the microprocessor perform calculations and speeds up computations and data manipulations dramatically.

CPU (central processing unit) — Also called a microprocessor or processor. The heart and brain of the computer, which receives data input, processes information, and executes instructions.

Default directory — The directory that DOS automatically uses to save and retrieve files.

Default drive —The drive that DOS automatically uses to save and retrieve files.

Default printer — The printer that Windows software will use unless the user specifies another printer.

Desktop — The initial screen that is displayed when an OS that has a GUI interface is loaded.

Device driver — A small program stored on the hard drive that tells the computer how to communicate with an input/output device such as a printer or modem.

DIMM (dual inline memory module) — A miniature circuit board used in newer computers to hold memory. DIMMs can hold 16, 32, 64, or 128 MB of RAM on a single module.

DIP (dual in-line package) switch — A switch on a circuit board or other device that can be set on or off to hold configuration or setup information.

Environment — As related to OSs, the overall support that an OS provides to applications software.

Expansion card — A circuit board inserted into a slot on the system board to enhance the capability of the computer.

Expansion slot — A narrow slot on the system board where an expansion card can be inserted. Expansion slots connect to a bus on the system board.

File — A collection of related records or lines that can be written to disk and assigned a name (for example, a simple letter or a payroll file containing data about employees).

File extension — A three-character portion of the name of a file that is used to identify the file type. The file extension follows the filename under DOS naming conventions.

Filename — The first part of the name assigned to a file. In DOS, the filename can be no more than eight characters long and is followed by the file extension.

Flash ROM — ROM that can be reprogrammed or changed without replacing chips.

GUI (graphical user interface) — A user interface, such as the Windows interface, that uses graphics or icons on the screen for running programs and entering information.

Hard drive — The main secondary storage device of a PC, a sealed case that contains magnetic coated platters that rotate at high speed.

Hard drive controller — A set of microchips with programs that control a hard drive. Most hard drive controllers today are located inside the hard drive housing.

Hardware — The physical components that constitute the computer system, such as the monitor, the keyboard, the system board, and the printer.

Jumper — Two wires that stick up side by side on the system board that are used to hold configuration information. The jumper is considered closed if a cover is over the wires, and open if the cover is missing.

Keyboard — A common input device through which data and instructions may be typed into computer memory.

Memory address — A number assigned to each byte in RAM. The CPU can use memory addresses to track where information is stored in RAM. Memory addresses are usually displayed as hexadecimal numbers in segment/offset form.

Monitor — The most commonly used output device for displaying text and graphics on a computer.

Mouse — A pointing and input device that allows the user to move a cursor around a screen and select programs with the click of a button.

Multitasking — When a CPU or an OS supporting multiple CPUs can do more than one thing at a time. The Pentium is a multitasking CPU.

Nonvolatile — Refers to a kind of RAM that is stable and can hold data as long as electricity is powering the memory.

Peripheral devices — Devices that communicate with the CPU, but are not located directly on the system board, such as the monitor, floppy drive, printer, and mouse.

Pixel — The smallest dot that can be addressed by software on a monitor screen. An image is composed of many pixels.

Plug and Play — A feature of system BIOS, Windows 9x, and Windows 2000 that automatically installs new hardware devices and assigns resources to them.

Port — A physical connector, usually at the back of a computer, that allows a cable from a peripheral device, such as a printer, mouse, or modem, to be attached.

Power supply — A box inside the computer case that supplies power to the system board and other installed devices. Power supplies provide 3.3, 5, and 12 volts DC.

Preemptive multitasking — A type of pseudomultitasking whereby the CPU allows an application a specified period of time and then preempts the processing to give time to another application.

Primary storage — Temporary storage on the system board used by the CPU to process data and instructions.

Printer — A peripheral output device that produces printed output to paper. Different types include dot matrix, ink-jet, and laser printers.

Program — A set of step-by-step instructions to a computer. Some are burned directly into chips, while others are stored as program files. Programs are written in languages such as BASIC and C++.

Program file — A file that contains instructions designed to be executed by the CPU.

Program jump — An instruction that causes control to be sent to a memory address other than the next sequential address.

Protected mode — An operating mode that supports multitasking whereby the OS manages memory, programs have more than 1024K of memory addresses, and programs can use a 32-bit data path.

Protocol — A set of rules and standards that two entities use for communication.

RAM (random access memory) — Temporary memory stored on chips, such as SIMMs, inside the computer. Information in RAM disappears when the computer’s power is turned off.

Real mode — A single-tasking operating mode whereby a program only has 1024K of memory addresses, has direct access to RAM, and uses a 16-bit data path.

ROM (read-only memory) — Chips that contain programming code and cannot be erased.

Root directory — The main directory created when a hard drive or disk is first formatted.

Secondary storage — Storage that is remote to the CPU and permanently holds data, even when the PC is turned off.

Server — A microcomputer or minicomputer that stores programs and data to be used remotely by other computers.

SIMM (single inline memory module) — A miniature circuit board used in a computer to hold RAM. SIMMs hold 8, 16, 32, or 64 MB on a single module.

Software — Computer programs, or instructions to perform a specific task. Software may be BIOS, OSs, or applications software such as a word-processing or spreadsheet program.

Startup BIOS — Part of system BIOS that is responsible for controlling the PC when it is first turned on. Startup BIOS gives control over to the OS once it is loaded.

Subdirectory — In DOS, a directory that is contained within another directory. Also called a child directory.

Suite — As applies to applications software, a collection of applications software sold as a bundle, whose components are designed to be compatible with one another. An example is Microsoft Office.

Swap file — A file on the hard drive that is used by the OS for virtual memory.

System board — The main board in the computer, also called the motherboard. The CPU, ROM chips, SIMMs, DIMMs, and interface cards are plugged into the system board.

System clock — A line on a bus that is dedicated to timing the activities of components connected to it. The system clock provides a continuous pulse that other devices use to time themselves.

Trace — A wire on a circuit board that connects two components or devices.

Video card — An interface card installed in the computer to control visual output on a monitor.

Virtual memory — A method whereby the OS uses the hard drive as though it were RAM.

Virtual real mode — An operating mode in which an OS provides an environment to a 16-bit program that acts like real mode.

Volatile — Refers to a kind of RAM that is temporary, cannot hold data very long, and must be frequently refreshed.

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