COMPUTER SYSTEM OVERVIEW 4 • Computer systems : consist of two principal components: Hardware – the “physical” parts of the computer system. (Chips, boards, cables, USB ports, monitor, printers, and so on.) Software – a collection of programs. A program is a collection of instructions to be executed by the computer’s hardware. • Hardware Components: CPU - Central Processing Unit "the brain“ Performs all the fundamental processing. Main Memory – (or Random Access Memory, RAM). A sequence of cells, accessed by address. Secondary Memory - hard disks, floppy disks, CD/DVDs, flash memory, etc. Input and Output Devices (I/O) - mouse, monitor, keyboard, etc.
COMPUTER SYSTEM OVERVIEW Main memory: – Fundamental data unit the bit – Bit - Binary digit (0 or 1) – Byte – Collection of bits. 8 bits forms one byte . – Word – Collection of words. A word is typically 4 bytes, or 32 bits. – Cells - Main memory is subdivided into units, called cells . – Address - The location of a memory cell. – With k bits you can store up to 2k different values
COMPUTER SYSTEM OVERVIEW • Program Execution: – Programs are stored permanently in secondary memory (e.g. on hard disk). – Programs are encoded as binary numbers ( machine code ). – When a program is to be run, it is copied ( loaded ) into main memory, and the CPU executes the instructions of the program. – Program may read data from secondary memory and input devices. – Results are written to output devices or to secondary memory.
COMPUTER SYSTEM OVERVIEW • Software Categories – Operating System Software – Application Software Operating System (OS): Manages the computer’s resources and acts as interface between applications and hardware. OS Responsibilities: Process management : Determines which programs (processes) to run. Memory management : Controls main memory. Input and Ouput control: Provides driver support, and basic input/output operations. Network Control : Controls communications. Enforces Security : Controls user-IDs and passwords and access to files.
COMPUTER SYSTEM OVERVIEW OS Examples : Windows XP, Unix (Linux, Solaris), Mac OS Application Software: Any software other than the operating system. Examples : word processors and text editors, spreadsheets, games, etc.
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Comparison Gen of Computers Considerably faster and smaller Smaller size and better performance Faster speed Slow speed Increased storage More flexibility with I/O Increased storage capacity Limited storage capacity Use of large scale and VLSI Use of integrated circuits Use of transistors Use of vaccum tubes 4 th Generation 3 rd Generation 2 nd Generation Ist Generation
Comparison Gen of Computers Increased use of (PC) microcomputers Sophisticated programs and languages for special applications Remote processing and time sharing High level programming language(cobol,fortran) Problem overs heating Modular design ,versatility and compatibility Extensive use of high level programming language Reduction in size and heat generation Symbolic language programming and huge size 4 th Generation 3 rd Generation 2 nd Generation Ist Generation