Computer Hardware

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Computer Hardware

• PC Operating Systems

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What is an operating system?

• An OS is the interface between the user and the
  computer hardware
• It provides the user and programmer with standard
  routines to access the hardware without resorting
  to machine language.
• This is true for a command driven O/S or GUI

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What does an O/S provide?

• Command line operating systems allow the user to
  type in a command to initiate a task e.g.
• The ability to type in a program name to run it
• The ability to write batch files to automate a
  sequence of tasks
• Dir command to view the contents of disk drives
• Copy command to copy files from one location to
  another
• Type command to view the contents of text files
• Ren command to rename files
• Ability to use switches to modify the behaviour
  of commands
• Some commands are internal (in memory) and some
  are external programs (stored on the boot disk)
  e.g.
• DIR is an internal command stored in memory
  (RAM)
• FDISK is an external command used to configure
  hard disks for use

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Graphical Operating Systems

• The most familiar graphical systems are Microsoft
  Windows and the Macintosh OS
• They perform the same tasks as the command line
  system but via a different user interface e.g.
• Point and double click an icon to run an
  application
• Open a window to view the contents of a disk
  drive
• Essentially they both do the same job
• The major benefit with graphical systems is that
  they can run multiple programs concurrently

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Common Operating Systems

• MSDOS command driven
• MS Windows - GUI
• UNIX - command driven(inc Solaris GUI)
• Linux GUI/cmd, a variant of Unix
• IBM OS/2 - GUI

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MSDOS

• Developed by Microsoft on license from IBM for
  their IBM PC in 1981
• Acronym forMicro Soft Disk Operating System

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Multi Tasking OS

• Multi tasking is the term for running multiple
  applications concurrently
• We now take for granted that under Windows a user
  can run many applications concurrently and this
  was a major selling point when Windows was
  initially released
• MSDOS was not a good multi tasking environment
  but some third party developers such as
  Quarterdeck allowed a crude form of multitasking
  under DOS which needed additional expanded
  memory which was very expensive
• Unix allows multitasking and was the mainstay of
  mainframe computers in the 1980s

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The Graphical User Interface

• In the late 1980s the IBM PC relied on the MSDOS
  O/S and a command prompt
• The Apple Macintosh on the other hand had a
  graphical user interface (GUI) which was much
  more user friendly
• With the advent of 80386 and 80486 based PCs the
  Windows environment became a reality as this
  processor could now address far more memory than
  its predecessors (the 80286 could only address
  16Mb!!)

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Device Drivers for the PC

• Device drivers are an interface between the
  physical hardware and the O/S. The driver
  software is normally written and supplied by the
  hardware vendors
• DOS and WINDOWS rely on these drivers to
  communicate with the many devices now available
  (printers, modems, cameras etc)
• 16 bit DOS device drivers (real mode)
• 32 bit native windows drivers

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Editable MSDOS Config files

• Autoexec.bat - example
• Config.sys - example
• MSDOS.SYS (hidden) - example

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Windows configuration files

• Early Windows such as 3.0 and 3.11 relied on
  MSDOS drivers and configuration files
• Windows 95 and later does not rely on the DOS
  config files so heavily and uses native 32bit
  Windows drivers when available
• O/S and application settings are stored in the
  Windows Registry (introduced in 3.11) which is
  accessed using regedit.exe
• This is made up of two physical files for Windows
  95-MESYSTEM.DATUSER.DAT
• NTUSER.DAT for Windows NT/2000/XP
• Windows ME copies any config settings to the
  registry but still relies on MSDOS
• In Windows NT, 2000 and XP the MSDOS config files
  are ignored altogether.

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Regedit.exe
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Windows NT/2000

• Is not based on MSDOS like Windows 95/98 and even
  ME
• Does not use autoexec.bat and config.sys and
  ignores them at bootup
• Does use BOOT.INI to find out where the O/S has
  been installed, boot.ini is also used in dual
  boot NT systems

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PC File Systems
O/S FAT16 FAT32 NTFS
DOS lt6.22 ?
DOS gt6.22 ? ?
Windows 98/ME ? ?
Windows NT4 ? ?
Windows 2000 ? ? ?
Windows XP ? ? ?
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MS DOS - Boot Sequence

• The BIOS (Basic Input / Output System) performs a
  system check and configures logical (COM and LPT
  ports) and plug-and-play (PnP) devices.
• The BIOS searches for a disk with a boot sector
  and loads that boot sector's volume boot code.
  (All formatted hard disks, floppy disks, and Zip
  and Jaz disks and some CD-ROMs have boot sectors,
  but not all disks contain operating system
  files.)
• The volume boot code examines the structures on
  the disk it is booting. If there is a problem,
  the boot process ends in an error.
• The volume boot code searches the root directory
  of the disk being booted for operating system
  files (for DOS these are IO.SYS, MSDOS.SYS, and
  COMMAND.COM).
• If OS files are not found the volume boot code
  displays the error message "Non-system disk or
  disk error--Replace and press any key when
  ready." (At this point the computer has already
  loaded and executed any code in the boot sector,
  even if the disk contains no operating system.)
• If OS files are found, the volume boot code
  transfers control to the OS (DOS).
• DOS processes the Windows registry, which sets up
  the system configuration for Windows.
• DOS runs CONFIG.SYS, which sets up the system
  configuration for DOS.
• DOS executes the commands in AUTOEXEC.BAT
  (erasing / setting temp directory, etc.).
• DOS starts Windows.

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Windows NT/2000 Boot Files

• The initial Power On Self Test (POST) initialises
  hardware components then the system BIOS
  identifies the boot device. Typically, this is a
  floppy disk or a hard disk.
• In the case of the hard disk, the BIOS reads the
  first physical sector on the disk, called the
  Master Boot Sector, and loads an image of it into
  memory. The BIOS then transfers execution to that
  image of the Master Boot Sector then called the
  Master Boot Record (MBR).
• The Master Boot Record contains the partition
  table and a small amount of executable code. The
  executable code examines the partition table and
  identifies the active (or bootable) partition.
• The Master Boot Record then finds the active
  partition's starting location on the disk and
  loads an image of its first sector, called the
  Boot Sector, into memory. The Master Boot Record
  then transfers execution to that Boot Sector
  image.
• The Boot Sector is responsible for locating the
  executable file, NTLDR.EXE, which continues the
  boot process. The following files are essential
  to boot windows NT
• NTLDR.EXE starts the boot process and reads
  BOOT.INI to build a boot loader menu
• NTLDR.EXE then loads the OS that the user chooses
• NTDETECT.COM runs if the user chooses Windows
  NT/2000 and examines available hardware then
  builds a hardware list
• NTLDR.EXE runs NTOSKRNL.EXE to begin the Windows
  NT load phases that initialise NT
• OTHER FILES
• NTBOOTDD.SYS - (Used if you are using SCSI
  disks with the SCSI BIOS disabled)
• BOOTSECT.DOS (Used if the user chooses another
  OS other than Windows NT

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Installing MSDOS

• Installation of DOS starts with the preparation
  of the hard disk using the FDISK utility.
• The PC is booted first from a (bootable) floppy
  disk
• Once the hard disk is partitioned, it is
  formatted and the necessary boot files are
  installed on it in the root directory
• All other external DOS command files and drivers
  are normally stored in the C\DOS directory
• Any configurations to the settings are made
  within the config.sys and autoexec.bat files
  (e.g. you may want to run a menu system when the
  PC boots)

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Installing Windows 98/ME

• All versions of Windows other than NT rely on
  MSDOS
• Therefore DOS needs to be installed first then
  Windows afterwards
• Later versions can be installed from a bootable
  CD without the need for DOS installation, it is
  more user friendly but still installs DOS files
  such as COMMAND.COM, IO.SYS and MSDOS.SYS
• Command line files are now stored in the
  C\WINDOWS\COMMAND directory

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Installing Windows NT/2000/XP

• The major difference is that NT and others based
  on NT do not rely on DOS although can run DOS
  programs
• To install, MS supply an install boot floppy disk
  set(4 disks)
• This boots to an NT environment and sets up your
  hard disk (like FDISK) then copies the necessary
  setup files to it
• The Windows directory is named WINNT instead of
  WINDOWS(except for XP which uses WINDOWS as
  default)
• Command.com has now gone and any command prompt
  commands such as DIR and COPY are provided from
  CMD.EXE in the C\WINNT\system32 directory which
  sets up a pseudo DOS environment
• All hard disk operations such as partitioning and
  formatting are performed within the GUI using
  disk manager

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Microsoft Windows

• Early versions of Windows were semi
  graphical/text based systems
• Windows 3.0 was the first version to get the
  industry interested in using Windows rather than
  DOS
• Windows 3.11 (for workgroups) fixed many bugs,
  was more stable and added networking features

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MS Windows versions

• Windows 286 1988/89
• Windows 3.0 - 1990
• Windows 3.1, 3.11 (for workgroups) 1991/92
• Windows 95 1994/95
• Windows 98, 98SE - 1997/98
• Windows ME 1999/2000/2001
• Windows NT 3.51, 4.0 / Workstation 1993 - 1998
• Windows 2000 Pro / Server 1999/2000/2001
• Windows XP Oct 2001/2002

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Windows XP Desktop
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XP Classic Start Menu