Booting Up

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Booting Up
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first 64K computer address space

• what is in a PCs memory when the computer is
  off?
• most of RAM is empty when the PC first powers up
• RAM is volatile because its contents are lost
  when power goes off
• but, two small parts are different

• when the PC first powers up, where is the
  operating system?

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battery-backed RAM

• battery-backed RAM contains a simple database
• also called the CMOS
• a program called Setup is used to modify it
• you can start Setup only while booting the
  computer
• its data describes hardware parameters
• time/date
• what disk drives are present
• what kind of display is present
• how much memory is present
• how fast some components should run
• etc.

• how does the configuration data get modified?
• plug and play devices
• the Setup program

4
the EEPROM

• the EEPROM contains the programs needed to start
  the computer
• also called the BIOS, or the firmware
• because it contains only programs, it can be
  read-only
• BIOS routines (a minimal keyboard/display driver)
• POST routines (e.g., RAM parity check, keyboard
  test)
• setup program lets users view or modify
  hardware settings
• bootstrap program searches disk drives for an
  operating system

• how does the BIOS get updated if its programs
  need to change?

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add-on boards also contain BIOS chips

• the motherboard BIOS contains code to access the
  keyboard, floppy drive, ATA (IDE) hard disk
  controllers, USB devices, and disk drives
• a computer system can contain several BIOS
  firmware chips
• plug-in adapter cards such as network interface
  cards and video boards often include their own
  BIOS
• complementing or replace the system BIOS code for
  the given component
• CMOS (Setup) database maps these extra BIOS
  programs into the low memory address space

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what is a disk drive?

• a piece of physical hardware
• non-volatile storage
• programs on a disk drive must be loaded into RAM
  before they execute
• disk drives must be subdivided into partitions
• the act of writing on a disk drive to partition
  it is called partitioning
• you have to know which OS will use the partition
  before you create it
• partitions have to be formatted with a particular
  file system
• typically, each OS uses a different file system
• PC partitions have one or more logical drive
  letters associated with them
• Solaris partitions have directories associated
  with them (mounted)

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more about disk drives

• what is fdisk?
• a utility from Microsoft for partitioning disks
• part of the original DOS 6.x operating system
• a more versatile utility Partition Magic
• what is a boot sector? (master boot record, or
  MBR)
• the first accessible sector on a drive
• it contains
• a table of (up to 4) partitions
• optionally, code to bootstrap an OS from the
  active partition
• the partition table in the boot sector contains
  up to 4 entries
• primary partition
• takes up one entry in partition table, and
  contains a single logical drive
• extended partition
• takes up 1 entry in partition table, and may
  contain multiple DOS, Linux or other partitions
  (logical drives in Windows)
• Solaris partition
• takes up 1 entry in partition table
• active partition
• a primary partition that is bootable

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starting Windows on an x86-based computer

• since 1981, all x86-based computers use the
  partition style known as the master boot record
  (MBR)
• first used by MS-DOS in 1981, and continued up
  through Windows XP Pro
• when you start your computer, the first code that
  executes is the BIOS
• BIOS loads the bytes from the MBR of the boot
  device into memory
• it then transfers control to the bytes just
  loaded into memory
• the MBRs first bytes are code to start loading
  the operating system
• but first, it has to find the operating system
• It looks that up in the partition table (stored
  in the end of the MBR)
• Because MBR is the only partition style available
  on x86-based computers running Windows XP or
  earlier, it is used automatically and you do not
  need to choose this style
• Dynamic disks were introduced in Windows 2000 and
  they provide features that basic disks do not,
  such as the ability to create volumes that span
  multiple disks, including fault-tolerant mirrored
  and RAID-5 volumes.
• Requires a GPT partition style
• GPT stands for GUID Partition Table
• GUID stands for Globally Unique ID

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MBR

• the first physical sector on a disk contains a
  data structure known as the Master Boot Record
  (MBR). The MBR contains the following
• a boot program (up to 442 bytes in size)
• a disk signature (a unique 4-byte number)
• a partition table (up to four entries)
• an end-of-MBR marker (always 0x55AA)

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enter GPT partitions and EFI

• Extensible Firmware Interface (EFI) is a
  specification that defines a software interface
  between an operating system and platform
  firmware.
• EFI is intended as a significantly improved
  replacement of the old legacy BIOS firmware
  interface historically used by all IBM PC
  compatible personal computers
• the EFI specification was originally developed by
  Intel
• now managed by the Unified EFI Forum and is
  officially known as Unified EFI (UEFI)
• Used first on Itanium processor systems
• Also used by 64-bit Windows versions
• Vista can use them as data disks (but not boot
  drives)
• XP Pro cannot use them at all

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kinds of hard drives today

• basic MBR disk Windows XP systems all use this
• basic GPT disk
• dynamic MBR disk
• dynamic GPT disk
• if using EFI, there also has to be a special
  partition containing the particular EFI code your
  computer system happens to need
• what are the implications of this?

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Boot Camp

• I have a MacBook capable of running both Mac OS X
  and Windows XP
• the laptop is 2 years old
• cost was 1200 300 for Windows XP Pro license
• it only has Mac OS 10.4, Tiger
• not 10.5, Leopard, the latest
• came with 512K, not enough memory to run Leopard
• how did I get it to run Windows?
• Mac OS 10.4 let me download a special program
  called Boot Camp
• it created a Windows partition, after which, I
  installed Windows XP Pro on that partition
• coupla years went by
• recently, my Windows XP install partition got
  sick I needed to restart Windows
• it died in a way that even Mac OS X was unable to
  redo the Windows partition
• so I also had to reinstall Mac OS X (10.4)
• Boot Camp was cripple-ware
• expired could no longer download it
• what to do?

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the end of this slideset
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• I have a MacBook with Apples Boot Camp program
  on it
• What does Boot Camp do?
• Can I just run Windows on my MacBook without