Operating System: BIOS

• Operating System Technology Concepts are covered in this lecture.

BIOS

• Basic Input/Output System (BIOS) is a computer program stored in EPROM.
• CPU uses BIOS to perform start-up procedures.
• BIOS determines available devices like keyboard, mouse, and video cards.
• BIOS loads the operating system (OS) into main memory.
• The BIOS program manages data flow between the OS and devices after startup.
• Neither the OS nor application programs require to know the details of hardware addresses.
• United Extensible Firmware Interface (UEFI) replaced BIOS in the early 21st century.
• UEFI handles larger drives and operates faster than BIOS.
• The boot process involves the PC turning on and BIOS initializing the hardware.
• BIOS is usually stored on an EEPROM.
• EEPROM stands for Electrically-erasable programmable ROM.
• BIOS begins the Power-On Self Test (POST) process when the PC is powered on.
• BIOS bridges all parts of the PC, interfaces between them and sets up the video display to accept basic VGA (Video Graphics Array).
• BIOS also initializes memory banks and grants the CPU access to all the hardware.
• BIOS scans the IO buses for hardware, identifies and maps access to the hard disks.

How Boot Occurs

• First the PC is turned on and the BIOS initializes the hardware.
• Next, the BIOS calls code stored in the Master Boot Record (MBR) at the start of disk 0.
• This leads to MBR loading code from the boot sector of the active partition.
• Finally the boot sector loads and runs the bootloader.

Master Boot Record (MBR)

• It loads the first 512 bytes from the hard drive of the selected boot device.
• These 512 bytes are commonly known as the MBR.
• MBR contains the partition table which is an index of up to four partitions on the same disk.
• Without a partition table, the entire disk is limited to one partition, as seen on floppy disks.
• MBR bootloaders load the OS bootloader to execute the OS.

Bootloader

• A bootloader is a computer program responsible for booting a computer, also called a boot manager or bootstrap loader.
• GNU GRUB (GNU GRand Unified Bootloader).
• NTLDR (NT loader) for Windows NT operating system.
• Windows Boot Manager (bootmgr) based on NTLDR.
• Once executed, the bootloader loads its configuration/database from files on the same partition.
• It optionally presents a boot menu with a list of operating systems.
• The bootloader locates and loads the kernel for the selected OS from the disk and hands off control of the PC to the OS.
• NTLDR is the default bootloader for Windows NT, 2000 and XP
• The BOOT.INI on the active partition contains a list of operating systems and their locations
• NTDETECT.COM is a helper application used by the NTLDR to detect hardware and identify devices.
• BOOTMGR is the Windows bootloader used from Windows Vista, 7, 8 and 10.
• List of operating systems is read from the BCD file in the BOOT directory on the active partition.
• BOOTMGR is self-contained and needs no external helper programs or routines.
• GRUB is the most-popular bootloader for Linux, but can boot numerous other OSes as well.
• GRUB's boot settings are stored in (GRUB2) or menu.lst (GRUB).
• GRUB is a modular bootloader that can load additional modules from disk.

BIOS vs UEFI

• BIOS reads the first sector of the hard drive to find the address of the next device or code to execute.
• BIOS also selects the boot device.
• BIOS works in 16-bit mode, limiting the amount of code that can be read and executed from the firmware ROM.
• Unified Extensible Firmware Interface (UEFI) stores all the information about initialization and startup in an .efi file instead of the firmware.
• This .efi file is stored on the hard drive inside a special partition called EFI System Partition (ESP).
• The ESP partition also contains the boot loader programs for the OS on the computer.
• UEFI is intended to replace BIOS.

Secured Boot

• Legacy boot BIOS starts any OS loader, malware could start before Windows.
• Modern boot uses native UEFI which only starts signed operating system loaders.
• The firmware enforces policy, only starts signed OS loaders and OS loader enforces signature verification of Windows components
• Results in malware unable to change boot and OS components

UEFI v Legacy BIOS

• BIOS uses the Master Boot Record (MBR) partitioning scheme, UEFI uses the GUID Partition Table (GPT).
• Max partition size in MBR is ~2TB, max partition size in UEFI is ~9 ZetaBytes.
• MBR can have at most 4 primary partitions, GPT can have 128 Partitions.
• MBR can store only one boot loader, GPT has a separate dedicated EFI System Partition (ESP) can store multiple bootloaders.
• Legacy BIOS do not offer secure boot, UEFI offers secure boot.
• Legacy BIOS uses VBIOS for Graphics output, UEFI BIOS uses GOP for Graphics output.
• Legacy BIOS uses Assembly language and takes long time to boot while UEFI uses C language for fast POST and boot.
• Legacy BIOS take time delay from S States while UEFI resumes faster from S states Sleep/Hibernate.

Basic Disk vs Dynamic Disk

• A basic disk uses a partition table for tracking partitions and volumes, while a dynamic disk uses a hidden logical disk manager (LDM) or virtual disk service (VDS).
• Basic disks are supported by all Windows OSs.
• Dynamic disks are only supported by Windows 2000, XP, 2003, 2008, 2011, 2012, Vista, Windows 7 and Windows 8.
• With basic disks, you can not change the capacity of a partition directly after it is created.
• You can expand the capacity of dynamic disk partitions without restarting, and no loss of data.
• Maximum capacity for a basic disk is 2TB. Partitions can be larger than 2TB in dynamic disks.
• If using MBR partition style, basic disks allow a maximum of four partitions. GPT styled basic disks can have a maximum of 128 partitions.
• Dynamic disks support unlimited number of partitions.
• Basic disks only allow primary or logical partitions, while dynamic disks allow simple, spanned, striped, mirrored, and RAID-5 volumes.
• Basic disks can be converted to dynamic disks without data loss. All volumes on the dynamic disk should be deleted to convert a dynamic disk to basic.

Partition: Basic and Logical

• Primary Partition is the hard disk location where both Windows OS and other data can be stored.
• A primary partition can be set active for BIOS to locate and must contain safe boot files.
• A logical drive is a hard disk partition created in an extended partition to install Windows or other files but is unable to be set active.

Dynamic Disk Volume

• A simple volume uses free space from a single disk that can be extended within the same disk or onto additional disks.
• A spanned value is created from the free disk space from multiple disks and cannot be mirrored.
• A mirrored volume duplicates data on two physical disks, provides data redundancy, but cannot be extended.
• Also known as RAID-1.
• A striped volume has interleaved data across two or more physical disks that cannot be mirrored or extended, also known as RAID-0.
• A RAID-5 volume is a fault-tolerant volume whose data is striped across an array of three or more disks.

File System

• The operating system keeps track of files by placing these files into a file.
• The steps involves are: Disk divided into tracks, tracks are divided into sectors, sectors are grouped into clusters and number of sectors in a cluster is determined by Size of the hard drive and File allocation system.
• These file allocation systems are FAT, FAT32, and NTFS.
• A cluster, also known as an allocation unit, consists of one or more sectors of storage space.
• Determines the minimum amount of space that an operating system allocates when saving the contents of a file to a disk.
• The number of sectors per cluster is dependent on the type of disk, version of OS, and size of the disk.
• Every sector contains 512 bytes, but NTFS allows users to change this number.
• Number of clusters per disk is determined by the filing system like FAT 16, FAT 32 and NTFS.

File Systems

• The chart shows the following file system details: File System, Max File Size and Max Partition Size.
• FAT16 = 2 GiB, 2 GiB.
• FAT32 = 4 GiB, 8 TiB.
• NTFS = 2 TiB, 256 TiB.
• ext2 = 2 TiB, 32 TiB.
• ext3 = 2 TiB, 32 TiB.
• ext4 = 16 TiB, 1 EiB.

Virtualization

• It can be checked from the Task Manager.
  • Open up the Task Manager by pressing the Ctrl + Shift + Esc keys, then go to the Performance tab.
• It can be also checked from the Systeminfo.exe program.
• Instructions to Enable Virtualization.
  • Reboot your computer.
  • Right when the computer is coming up from the black screen, press Delete, Esc, F1, F2, or F4.
  • Each computer manufacturer uses a different key.
• BIOS Buttons can be identified.
  • ASRock: F2 or DEL.
  • ASUS: F2 for all PCs, F2 or DEL for Motherboards.
  • Acer: F2 or DEL.
  • Dell: F2 or F12.
  • ECS: DEL.
  • Gigabyte / Aorus: F2 or DEL.
  • HP: ESC, F10.
  • Lenovo (Consumer Laptops): F2 or Fn + F2.
  • Lenovo (Desktops): F1.
  • Lenovo (ThinkPads): Enter then F1.
  • MSI: DEL for motherboards and PCs.
  • Microsoft Surface Tablets: Press and hold volume up button.
  • Origin PC: F2.
  • Samsung: F2.
  • Toshiba: F2.
  • Zotac: DEL.
• Enable virtualization and the setting may be called VT-x, AMD-V, SVM, or Vanderpool.
• Enable Intel VT-d or AMD IOMMU if the options are available.
• Tips to run: In run (win key + r) write MSINFO32 or msconfig.