Transcript Document
The components of a computer Types of computer Computers can be categorised into four types Microcomputers - desktop, laptop, notebook and palmtop personal computers (PCs) - used in businesses, schools/colleges and homes - cost from a few hundred pounds to a few thousand Minicomputers - often used as multi-user systems, with 100’s of workstations or terminals attached to a central minicomputer, e.g. EPOS. - cost from £10,000 to about £150,000. Mainframe computers - used by large organisations which may have 1000’s of terminals, often remote - cost ££ hundreds of thousands Supercomputers - largest category of computer used mostly by scientific & industrial research departments, NASA, the Weather Centre, stock exchanges - cost ££ millions CPU Controls the transmission of data from input devices to memory Processes the data held in main memory Controls the transmission of information from main memory to output devices How CPUs work? A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a single chip. • Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern microprocessors contain complete floating point processors that can perform extremely sophisticated operations on large floating point numbers. • A microprocessor can move data from one memory location to another. • A microprocessor can make decisions and jump to a new set of instructions based on those decisions. Clock Speed To synchronize the steps of the fetch-decode execute cycle, all processors have an internal clock which generates regularly timed pulses. All activities of the fetch-decode-execute Cycle must begin on a clock pulse. Word Size The number of bits that the CPU can process simultaneously. Normally groups of 8, 16, 32, 64, 128 bit words are processed as a unit during input, output and logic instructions. Word size is a major factor in determining the speed of a processor. Bus Size Buses are the lines along which data is transmitted. This data can be in the form of data and instructions as well the addresses of the data and the instructions. The width of a data bus determines how many bits can be transmitted simultaneously and the maximum address which can be referenced. Bus Size con’t For 8 bits 28 – 1 = 255 i.e. 0 to 255 which is 256 locations. An address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory A data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory An RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed location A clock line that lets a clock pulse sequence the processor A reset line that resets the program counter to zero (or whatever) and restarts execution Instruction Set Instructions in machine language are in the form of binary codes, with each different processor using different codes for the instruction set supported by its hardware. The instruction set for a typical computer includes the following types of instructions: Data Transfer Arithmetic Operations Logical Operations Test and Branch Instructions Main memory Instructions and data are held in main memory, which is divided into millions of individually-addressable storage units called bytes. One byte can hold one character, or it can be used to hold a code representing, for example, a tiny part of a picture, a sound, or part of a computer program instruction. The total number of bytes in main memory is referred to as the computer’s memory size. Computer memory sizes are measured as follows: 1 Kilobyte (Kb) 1 Megabyte (Mb) 1 Gigabyte (Gb) 1 Terabyte (Tb) = = = = 1000 bytes (to be exact, 1024 bytes) 1,000,000 (1 million) bytes 1,000,000,000 (1 billion) bytes 1,000,000,000,000 (1 trillion) bytes Random Access Memory (RAM) ‘Ordinary’ memory Used for storing programs which are currently running and data which is being processed. This type of memory is volatile - it loses all its contents as soon as the machine is switched off. Read Only Memory (ROM) Non-volatile, with contents permanently etched into the memory chip at the manufacturing stage Used for example to hold the bootstrap loader, the program which runs as soon as the computer is switched on and instructs it to load the operating system from disk into memory. PROM Short for programmable read-only memory, a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike RAM, PROMs retain their contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM. An EPROM (erasable programmable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased. What is an EPROM? EPROM(Erasable Programmable Read Only Memory) can be programmed and erased enabling them to be re-used. Erasure is accomplished using an UV (Ultra Violet) light source that shines through a quartz erasing window in the EPROM package. Acronym for erasable programmable read-only memory, and pronounced ee-prom, EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner. An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery. What is an EEPROM? Pronounced double-ee-prom or e-e-prom, short for electrically erasable programmable readonly memory. EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM. EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster. What is a Flash EPROM? A flash EPROM is similar to an EEPROM except that flash EPROMs are erased all at once while a regular EEROMs can erase one byte at a time. In- circuit writing and erasing is possible because no special voltages are required. To accomplish in-circuit operation, you have to write special application software routines. Flash EPROMs are also called nonvolatile memory.. Cache Memory Very fast memory used to improve the speed of a computer, doubling it in some cases Acts as an intermediate store between the CPU and main memory Stores the most frequently or recently used instructions and data for rapid retrieval Generally between 1Kb and 512Kb Much more expensive than normal RAM Memory Cache speeds up a computer by storing data the computer has recently used. There are 2 types : Internal & External External Cache If the computer cannot find what it needs in the Internal Cache, it looks in the external cache. This is usually located on the Motherboard. In some CPU chips the External cache is built in. Internal Cache When the computer needs data it first looks in the Internal cache. This is located on the CPU chip and provides the fastest way for the computer to get data. Virtual memory Space on a hard disk used to temporarily store data and swap it in and out of RAM as needed. Motherboard This is the main circuit board that all of the other internal components connect to. The CPU and memory are usually on the motherboard. Other systems may be found directly on the motherboard or connected to it through a secondary connection. For example, a sound card can be built into the motherboard or connected through PCI (Peripheral Component Interface). Auxiliary Storage Hard disks - all standalone PCs have in-built hard disk - typical capacity for Pentium PC is >= 40 Gb - used for storing software including the operating system, other systems software, application programs and data Floppy disks - thin sheet of mylar plastic in hard 3½” casing - capacity 1.44Mb CD-ROM - holds about 700Mb Zip disks - hold up to 250Mb Power supply An electrical transformer regulates the electricity used by the computer. Hard disk This is large-capacity permanent storage used to hold information such as programs and documents. Operating system This is the basic software that allows the user to interface with the computer. Integrated Drive Electronics (IDE) Controller This is the primary interface for the hard drive, CDROM and floppy disk drive. Peripheral Component Interconnect (PCI) Bus The most common way to connect additional components to the computer, PCI uses a series of slots on the motherboard that PCI cards plug into. SCSI Pronounced "scuzzy," the small computer system interface is a method of adding additional devices, such as hard drives or scanners, to the computer. AGP Accelerated Graphics Port is a very high-speed connection used by the graphics card to interface with the computer. Sound card This is used by the computer to record and play audio by converting analog sound into digital information and back again. Graphics card - This translates image data from the computer into a format that can be displayed by the monitor. Parallel Port USB Ports Serial Ports SERIAL PORT Considered to be one of the most basic external connections to a computer, the serial port has been an integral part of most computers for more than 20 years. Although many of the newer systems have done away with the serial port completely in favor of USB connections, most modems still use the serial port, as do some printers, PDAs and digital cameras. Few computers have more than two serial ports. Parallel Ports If you have a printer connected to your computer, there is a good chance that it uses the parallel port. While USB is becoming increasingly popular, the parallel port is still a commonly used interface for printers. Parallel ports can be used to connect a host of popular computer peripherals: • Printers • Scanners • CD burners • External hard drives • Iomega Zip removable drives • Network adapters • Tape backup drives Universal Serial Bus (USB) Ports The goal of USB is to end all of these headaches. The Universal Serial Bus gives you a single, standardized, easy-to-use way to connect up to 127 devices to a computer. Just about every peripheral made now comes in a USB version. A sample list of USB devices that you can buy today includes: Printers Scanners Mice Joysticks Flight yokes Digital cameras Webcams Scientific data acquisition devices Modems Speakers Telephones Storage devices such as Zip drives Video phones Network connections Connecting a USB device to a computer is simple -- you find the USB connector on the back of your machine and plug the USB connector into it. The rectangular socket is a typical USB socket on the back of a PC. A typical "B" connection A typical USB connector, called an "A" connection Input and output devices Input devices - Keyboard - mouse - barcode readers - Scanners Output devices - printer - plotter - VDU Can you name some others?