COMPUTER FUNDAMENTALS(neelam pant)

Basics of Computers and it operations :

Basics of Computers and it operations The computer system A computer also known as computer system (since it is made up of integrated components as input and output devices, storages, central processing unit) works for a common objective of processing of the data. It consists of six elements: Hardware Software People Procedures Data Connectivity

The personnel who operates the hardware or develop the software they can be a PC user, a data entry operator in any organization, a software developer in a process, a hardware or networking engineer or a graphic designer.   Procedures are the rules, regulations, methods through which a computer responds to software. The operating system acts as an interface between the user and the machine.   Data are raw facts or figures. After processing these data becomes information.   The system of interconnecting computers by cable, satellite, Internet etc is called connectivity. :

The personnel who operates the hardware or develop the software they can be a PC user, a data entry operator in any organization, a software developer in a process, a hardware or networking engineer or a graphic designer. Procedures are the rules, regulations, methods through which a computer responds to software. The operating system acts as an interface between the user and the machine. Data are raw facts or figures. After processing these data becomes information. The system of interconnecting computers by cable, satellite, Internet etc is called connectivity. The physical components of a computer system such as electromagnetic and mechanical devices, keyboard, VDU, printers, plotter, mouse etc are parts of hardware. Software is a set of instructions that tells the hardware how to perform a task. System software, utility software & application software are some examples. System software can interact with the hardware directly. System software is most complex form of software followed by utility and application. ( Brooks, 1975 )

Computer System Architecture:

Computer System Architecture

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A computer system or its architecture consists of three main elements Input Central Processing Unit Output I nput unit is a medium through which a user can communicate with the computer. Keyboard, mouse, MICR, OMR, OCR, scanner, microphone are some input devices. The output unit is responsible for converting the processed results in back into the form that we can understand. VDU, printers, speakers, plotters are some examples. CPU commonly called the processor performs all the data processing and also controls the operations of the computer. Its main structural components are Control Unit, ALU, Registers and CPU Interconnections. Control Unit controls all CPU operations and hence the computer system by routing the selected data items to the selected processing hardware at the right time. A rithmetic L ogic U nit performs all data processing, it’s a collection of logic circuits designed to perform arithmetic (addition, subtraction, division, multiplication) and logical (not, and, or, exclusive-or etc) operations. Registers forms internal storage within CPU that is required during processing CPU Interconnections provides the communication channels among the Control Unit, ALU and registers.

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Intel 8086 This processor contains 4 general purpose registers, 4 pointers and index registers, 4 segment registers, an instruction pointer and a set of 1 bit status and control flags

MS-DOS Boot Process :

MS-DOS Boot Process When the computer is switched on, a series of steps are executed before the user can start interacting with the computer. The processor executes the ROM-BIOS instructions. These instructions are permanently fused in ROM chip and are activated each time the power is switched on. The first of ROM-BIOS instructions is the start-up routine that checks if all parts are in good working conditions. It checks the RAM, all connections to input/output/storage devices. This testing activity is also commonly known as POST (Power on self test). The next ROM-BIOS instruction is “bootstrap” which brings in DOS from the disk into memory. In bootstrap the ROM-BIOS attempts to read a boot record from the disk. The boot record is found in the boot sector which is the first sector of the disk. In order to load the boot record ROM-BIOS searches A: or C: drives and if not found displays an error message stating that boot record not found!

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If ROM-BIOS is able to read a boot record, it hands over control to the short program on the boot record. These instructions now access two files from the disk called the IBMBIO.COM and IBMDOS.COM which are both part of the DOS. DOS is made up of IBMBIO.COM ( IO.SYS ), IBMDOS.COM ( MSDOS.SYS ) & COMMAND.COM. After IO.SYS and MSDOS.SYS are loaded next the file CONFIG.SYS is loaded which allows the user to use certain parameters with DOS. ( eg . FILES = 20, if this statement is totally absent DOS allows to use only 8 files to be opened at a time out of which 5 are DOS files.) The last step of the bootstrap process is loading of COMMAND.COM into memory. Once that is completed the computer is under the control of the operating system. Finally the computer asks for system time and date. Pressing enter twice will bring the DOS PROMPT C:\ or A:\

Windows Bootup Process   :

Windows Bootup Process Booting Up It is useful to understand what happens behind the scenes when you switch on your computer from a cold idle machine to an operable and functional system. There are essentially two forms of booting - the soft boot and the hard boot. The warm boot or hard boot involves powering the computer up from an initial zero power supply. A cold boot on the other hand takes place when a software application or operating system triggers the computer to perform a reboot. A successful boot is dependent on 3 conditions - the hardware, BIOS and operating system files to function without errors. When an error occurs, you will be notified by error messages, beeping sounds or in the worst scenario, a blank screen.

Bootup Process   The bootup process is a list of detailed procedures that the system undergoes to perform all system checks and load all necessary files to bring the computer to an operable state.   The Windows XP bootup process comprises of the following procedures:   :

Bootup Process The bootup process is a list of detailed procedures that the system undergoes to perform all system checks and load all necessary files to bring the computer to an operable state. The Windows XP bootup process comprises of the following procedures: The Power-On Self Test Phase As soon as you power up your computer, a self-test is performed by the power supply to ensure that the volume and current levels are correct before the Power Good signal is sent to the processor. When this first stage is cleared, the microprocessor will then trigger the BIOS to perform a series of operations

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BIOS ROM Phase The BIOS, also known as the Basic Input Output System is a firmware or set of instructions that resides on a ROM chip as contained in the motherboard. It first carries out the P.O.S.T that performs and verifies all initial hardware checks, such as checking if the system is initialized by a warm or cold start, detecting the presence of peripheral devices and the amount of memory present. It then accesses the information stored in the CMOS chip, DIP switches, jumpers and assigns the necessary system resources. After this, the hardware' firmware will individually carry out its own diagnostic test such as S.M.A.R.T. The system will now attempt to determine the sequence of devices to load based on the settings stored in the BIOS to start the operating system. It will start by reading from the first bootup device. If it points to the floppy drive, it then searches for a floppy disk. If it does not detect a bootable diskette in the floppy drive, the system displays an error message. If the floppy drive does not contain a diskette, it bypasses the first bootup device and detects the second device, which is usually the hard disk. It'll then start by reading the boot code instructions located in the master boot record and copies all execution into the memory when the instructions are validated and no errors are found.

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Boot Loader Phase Control is then passed on to the partition loader code which accesses the partition table to identify the primary partition, extended partitions and active partition which is needed to determine the file system and locate the operating system loader file - NTLDR. NTLDR will then switch the processor from real-mode to 32 bit protected mode which memory paging is enabled. NTLDR will call upon the boot.ini file which is located at the root directory to determine the location and entries of the operating system boot partition. At this point in time, the bootup menu is displayed on the screen to allow you to select an operating system to start from if you have more than 2 operating systems installed in your computer. NTLDR will pass all information from the Windows registry and Boot.ini file into Ntoskrnl.exe

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Operating System Configuration Phase Ntoskrnl will begin to load the XP kernel, hardware abstraction layer and registry information. After this is completed, the control is passed over to the DOS based Ntdetect.com program which collects and configures all installed hardware devices such as the video adapters and communication ports. Ntdetect.com then searches for hardware profiles information and load the essential software drivers to control the hardware devices. Security & Logon Phase Lastly, Ntoskrnl.exe will start up Winlogon.exe which triggers the Lsass.exe or Local Security Administration which is the logon dialog interface that prompts to select user profile and verifies necessary credentials before being transferred to the Windows desktop.