Computer Hardware ,Booting Processes-1.pdf
- 1. BOOTING PROCESS By Mvula 18th August, 2005 1 COMPUTER HARDWARE
- 2. Objectives At the end of this lesson students should be able to: Define booting process Explain the booting process Differentiate booting process of windows or linux.... Trouble shoot booting process problems and usage of primary memory usage during the booting process 18th August, 2005 2
- 3. Why is Booting Process Required ? Hardware doesn’t know where the operating system resides and how to load it. Need a special program to do this job – Bootstrap loader. E.g. BIOS – Boot Input Output System. Bootstrap loader locates the kernel, loads it into main memory and starts its execution. In some systems, a simple bootstrap loader fetches a more complex boot program from disk, which in turn loads the kernel. 18th August, 2005 3
- 4. How Boot process occurs ? Reset event on CPU (power up, reboot) causes instruction register to be loaded with a predefined memory location. It contains a jump instruction that transfers execution to the location of Bootstrap program. This program is form of ROM, since RAM is in unknown state at system startup. ROM is convenient as it needs no initialization and can’t be affected by virus. 18th August, 2005 4
- 6. Tasks performed at boot up Run diagnostics to determine the state of machine. If diagnostics pass, booting continues. Runs a Power-On Self Test (POST) to check the devices that the computer will rely on, are functioning. BIOS goes through a preconfigured list of devices until it finds one that is bootable. If it finds no such device, an error is given and the boot process stops. Initializes CPU registers, device controllers and contents of the main memory. After this, it loads the OS. 18th August, 2005 6
- 8. Tasks performed at boot up (Contd) On finding a bootable device, the BIOS loads and executes its boot sector. In the case of a hard drive, this is referred to as the master boot record (MBR) and is often not OS specific. The MBR code checks the partition table for an active partition. If one is found, the MBR code loads that partition's boot sector and executes it. The boot sector is often operating system specific, however in most operating systems its main function is to load and execute a kernel, which continues startup. 18th August, 2005 8
- 9. Secondary Boot Loaders If there is no active partition or the active partition's boot sector is invalid, the MBR may load a secondary boot loader and pass control to it and this secondary boot loader will select a partition (often via user input) and load its boot sector. Examples of secondary boot loaders GRUB – GRand Unified Bootloader LILO – LInux LOader NTLDR – NT Loader 18th August, 2005 9
- 10. Booting and ROM System such as cellular phones, PDAs and game consoles stores entire OS on ROM. Done only for small OS, simple supporting hardware, and rugged operation. Changing bootstrap code would require changing ROM chips. EPROM – Erasable Programmable ROM. Code execution in ROM is slower. Copied to RAM for faster execution. 18th August, 2005 10
- 11. Example : DOS After identifying the location of boot files, BIOS looks at the first sector (512 bytes) and copies information to specific location in RAM (7C00H) - Boot Record. Control passes from BIOS to a program residing in the boot record. Boot record loads the initial system file into RAM. For DOS, it is IO.SYS . The initial file, IO.SYS includes a file called SYSINIT which loads the remaining OS into the RAM. SYSINIT loads a system file MSDOS.SYS that knows how to work with BIOS. One of the first OS files that is loaded is the system configuration file, CONFIG.SYS in case of DOS. Information in the configuration file tells loading program which OS files need to be loaded (e.g. drivers) Another special file that is loaded is one which tells what specific applications or commands user wants to be performed as part of booting process. In DOS, it is AUTOEXEC.BAT. In Windows, it’s WIN.INI . 18th August, 2005 11
- 12. Summarised Booting Process Tasks that are carried during booting process are:: Turn on the Power button. CPU pins are reset and registers are set to specific value. CPU jump to address of BIOS (0xFFFF0). BIOS run POST (Power-On Self-Test) and other necessary checks. BIOS jumps to MBR (Master Boot Record). Primary Bootloader runs from MBR and jumps to Secondary Bootloader. Secondary Bootloaders loads Operating System. 18th August, 2005 12
- 13. Dual Booting Process Most likely. Most computers can be configured to run more than one operating system. Windows, mac OS, or Linux can happily coexist on one physical computer. The computer's hard drive is divided into multiple "partitions," then install different operating systems in each partition. With a dual-boot setup, the computer must be rebooted to switch from one OS to another. During the boot sequence, a list of available operating systems is presented to the user. 18th August, 2005 13
- 14. Information When installing an OS on a computer from scratch, here is how the partition table is created. The hard disk is denoted as “hda” where hd=hard disk, and the third letter could mean the hard-disk on the system. For e.g. the first hard disk is “hda”, the second is “hdb”. When the partitioning is done, “hda0” is the place of MBR. “hda1” is the primary partition. Then a secondary partition may be created which is further subdivided into logical drives. Another OS could be installed on any of these logical drives. hda0 – MBR hda1 – Primary Partition e.g. Windows XP hda2 – Secondary Partition hda3 – Logical Drive 1 (FAT32 or NTFS partition) hda4 – Logical Drive 2 (FAT32 or NTFS partition) hda5 – Logical Drive 3 (Swap for Linux Partition) hda6 – Logical Drive 4 (Root for Linux Partition) The above example is a simple example. Specific cases can be different. 18th August, 2005 14
- 16. EFFECTS ON BOOT SECTOR What is the effect on boot sector and boot loader when you install two OS, for e.g. Windows and Linux in two separate partitions ? Suppose, you install Windows first. The default boot loader installed in MBR is NTLDR and contains information regarding the active partition of Windows. When you install Linux on this system, the installation prompts to overwrite a new secondary boot loader which identifies both Windows and Linux active partitions and therefore we get a choice of booting the desired OS when the system is started. In contrast, if Linux is installed first and then Windows, the Windows Installer overwrites the MBR with its own boot loader which doesn’t recognize the Linux active partition. This creates a problem. The problem can be corrected by using a LiveCD or any bootable disc which can be used to reinstall a secondary boot loader which identifies both the OS and gives true choice. 18th August, 2005 16
- 17. Trouble shoot booting process It can be frustrating when a PC doesn’t boot properly and knowing where to start fixing a computer can be difficult. Maybe the computer doesn't turn on at all, maybe it powers up but shuts right down, or maybe it blue screens There are many potential causes of such problem, 18th August, 2005 17
- 18. Trouble shoot booting process Depending on the specifics of your situation, If you’ve plugged in a USB flash or any other peripheral such as a keyboard, mouse, or you’ve recently added a new storage device, or Updating your BIOS since then your computer has never successfully booted. Before changing any BIOS settings, try to unplug all attached peripherals from your computer. This includes everything other than the power cable, the display cable attached to your monitor, a keyboard, and any other attached peripherals like external hard drives or even USB-powered mice can potentially cause issues with power, driver conflicts, or issues with boot order, and can keep a system from booting to the OS. 18th August, 2005 18
- 19. BIOS Error Messages If your system successfully boots to your OS without any devices plugged in, attach each one individually, and restart until you find the peripheral causing the problem. Once you’ve eliminated external peripherals as a culprit, it’s time to check the BIOS for error messages. If the BIOS detects a hardware issue, it will tell you before you even have access to the BIOS menu. The error message will vary depending on the BIOS Here are a few examples of error messages. :CPU fan not detected Fan or cooler issue Key board/mouse not detected BOOT Device Error - There is an issue with one of your storage drives and so on 18th August, 2005 19
- 20. Questions Difference between Boot Loader and Boot Manager ? Basically, these two are different but are sometimes combined into a single program. IBM's Boot Manager, Power Quest's Boot Magic and V Communications' System Commander are some examples of boot managers. Dual booting is the act of installing multiple operating systems on a computer, and being able to choose which one to boot when switching on the computer. The program, which makes dual booting possible is called a boot loader. 18th August, 2005 20