An overview of Computer System Unit-1 An overview of Computer System

Anatomy of a digital Computer Definition of Computer A device that accepts data, processes the data in accordance with a stored program, generates results, and usually consists of input, output, storage, arithmetic, logic, and control units. A machine for manipulating data according to a list of instructions known as a program. …cntd

Block Diagram of Digital Computer Random-access memory (RAM) Central processing unit (CPU) Input-output processor (IOP) Input devices Output Block diagram of a digital computer

Block Diagram of Digital Computer A digital computer consists of a number of processors interconnected with memory and Input/Output devices A Processor or CPU (Central Processing Unit) fetches instructions from memory, and executes them one after another A Memory is where programs and data are stored I/O devices allow for interaction between users and computer (printers, keyboard, mice… )

Generations of Computers First generation: Vacuum tube computers (1940s - 1950s) First Generation Electronic Computers used Vacuum Tubes Vacuum tubes are glass tubes with circuits inside. Vacuum tubes have no air inside of them, which protects the circuitry.

Generations of Computers Second generation (1950s): Transistors Uses Silicon developed in 1948 won a Nobel prize on-off switch Second Generation Computers used Transistors, starting in 1956 Replaced vacuum tubes with Transistors

Generations of Computers Third generation (1960s and 1970s): Integrated circuits Third Generation Computers used Integrated Circuits (chips). Integrated Circuits are transistors, resistors, and capacitors integrated together into a single “chip” Operating System Software – Instructions for Computer Operating system is set of instructions loaded each time a computer is started Program is instructions loaded when needed

Generations of Computers Fourth generation (late 1970s through present): LSI and VLSI Personal computers, computer networks, WWW, etc. The First Microprocessor – 1971-Intel 4004 Microprocessor The 4004 had 2,250 transistors 108Khz Called “Microchip”

Generations of Computers Very Large Scale Integrated Circuit (VLSIC) Transistors, resistors, and capacitors 4004 had 2,250 transistors where Pentium IV has 42 MILLION transistors

Generations of Computers Fifth generation- 21st Century Computing Great increases in speed, storage, and memory Increased networking, speed in Internet PDAs Cell Phone/PDA WIRELESS!!!

Major Hardware Components of a Computer System CPU Main Memory Secondary Memory Input Devices Output Devices

Central Processing Unit Control Unit: works with the operating system to move data between auxiliary storage and main memory; and between main memory and the ALU Arithmetic/Logic Unit (ALU): processes data arithmetically (addition, subtraction, multiplication, division) or logically (greater than, less than, equal to) Main Memory: contains both program instructions and the data that is required. A single machine can have multiple CPUs to share processing tasks (co-processors, multiprocessing), but each CPU can execute only a single task.

Inside the System Unit Main component: motherboard Circuit board that “houses” integrated circuits (microscopic elements … wires, transistors, etc…) required to make the digital pulse flow inside of the computer. Pulses flow from component to component via the “bus”

Motherboard (cont.) Attachments to the motherboard include: Main Memory: types of main memory include: RAM - temporary (includes virtual memory storage). Include RAM cache ROM - permanent When add main memory, make sure add-on chips are compatible Real time clock (current date and time) Microprocessor or CPU (central processing unit) Control Unit: traffic cop portion of the CPU ALU: arithmetic logic unit processes all math and logical operations performed by the computer

Access Speed Increases Storage Capacity Decreases Primary & Secondary Storage Media Semiconductor Memory Magnetic Disks Floppy Disk Hard Disk, RAID Magnetic Tape Optical Disks CD-ROM, CD-R CD-RW DVD Access Speed Increases Storage Capacity Decreases Cost per Bit Increases Direct Access Sequential Secondary Storage Primary Storage

Memory Units- a unit for measuring computer memory Unit - any division of quantity accepted as a standard of measurement or exchange; "the dollar is the United States unit of currency"; "change per unit volume" Nibble - a small byte Byte - a sequence of 8 bits (enough to represent one character of alphanumeric data) processed as a single unit of information

Memory Units ..cntd Sector - the minimum track length that can be assigned to store information; unless otherwise specified a sector of data consists of 512 bytes Block - a sector or group of sectors that function as the smallest data unit permitted; "since blocks are often defined as a single sector, the terms `block' and `sector' are sometimes used interchangeably"

Main Memory Stores Instructions and Data Stored Program Concept Random Access Memory (RAM): allows data and instructions to be accessed randomly from any memory location (address). Primary storage. Volatile - lost when power is turned off Read Only Memory (ROM): usually contains programs that help the computer system operate: can only be read: cannot be written to or altered by the user (usually) ROM is not volatile

Main Memory Data and instructions are stored as BITS (binary digits). Everything from our world is translated into a computer recognizable format called binary (zeros or ones) The combination of binary digits represents our letters or numbers. One character represented is equal to a byte. Memory capacity is measured in bytes. Today’s most common measurement is megabytes Kilo = 1,000 (KB) Thousand Mega = 1,000,000 (MB) Million Giga = 1,000,000,000 (GB) Billion Bytes are composed using either the ASCII coding system (7 bits = character) or EBCDIC (8 bits = character)

Input Devices Input Devices are used to input the data to computer system. These are as follows Keyboard Mouse Trackball Touch Screen Optical Character Recognition MICR Scanners etc.

Output Devices Output Devices are used to take output from computer system. These are as follows Monitor Printer Plotter