What are the boot process steps?
- A power is turned on and stable power supply is established for the motherboard to reset the processor.
- Next, the processor starts with the computer fan turning on and clock cycles to start. The Computer needs to be booted.
- The reset command in the CPU triggers the instruction at a specific location of the BIOS.The specifiic location contains a Jump instruction to the actual start-up step program in the BIOS
- Booting starts with POST(Power-On-Self-Test). This checks multiple conditions such as if the system is running fine, timer is running, peripherals are checked and checking if the BIOS is not corrupted. Results of POST→ BEEP.
- Firstly, after the successful POST the video card is initialized to show the initial messages on the screen.
- Next, the BIOS/UEFI initializes the hardware as far as possible(rudimentary) such as Networking cards,RAM, soundcards, etc.
- The BIOS now searches for the Operating system through the boot drive in hardware(can be on hard disk, floppy disk, etc).
How does the BIOS search for the O.S on hard disk?
On a Master Record Record(MBR) of the first sector of the selected hard drive, the information on the boot loader(code) is executed. The MBR first loads the kernel(core) of the Operating system. Next, other device drivers are loaded.
- Once all device drivers are loaded, the GUI starts and personal setting are started .The computer is now ready for use.
What does booting the computer mean?
Booting the computer means activating the software step-by-step , one after the other.
When does booting start?
Booting really starts with the start-up process on the BIOS/UEFI.
First thing after a successful POST?
It is to initialize the video card to show the initial messages on the screen. It can only initialize rudimentary video cards, and not any 3D-level graphic video cards which would additional device drivers.
Where is the BIOS/UEFI stored?
The BIOS/UEFI is stored in the ROM of the motherboard.
What is the role of memory in the boot process?
When a computer boots, it can only access part of the storage in the ROM where the BIOS is located. The BIOS’s role is not only for the POST but it can also access the main memory. Hence, when the BIOS boots the OS, it runs it on the main memory.
What is the trusted platform module?
A TPM is a specialized chip that helps endpoint devices to be encrypted by RSA encryption for hardware authentication. It has an endorsement key(EK) private to the device. The Storage Root Key(SRK) is created when a user takes control of the device, and is created through the EK’S and user’s password.
What makes the BIOS updated?
BIOS can only boot from devices with less than 2.2 TB while the standard drive these days are 3+ TB.
BIOS runs in 16 bit processor mode with only 1 MB space to execute.
The BIOS can’t initialize multiple hardware devices at once, hence it is a slow booting process.
What makes UEFI better than BIOS for booting?
In BIOS, the Master Boot Record(MBR) searches for the first sector of the boot device. Instead, it creates a list of all bootable drives called Service Partitions. During the POST process, the UEFI scans all the valid service partitions for a valid GUID (Globally Unique Identifiers) Partition table.
What is a GUID partition table (GPT)?
A GPT is an improvement over the Master Boot Record(MBR) of the BIOS because it is a standard that creates a partition table layout on a physical storage device that is on a PC or server such as hard-drives or solid-state drive , usually globally unique identifiers(GUID). It directly loads the OS from the right partition.
What are the Advantages of UEFI over BIOS?
- Size- The UEFI can theoretically boot drives up to 9.2 zettabytes
- Speed- The processor can be in 32 or 64 bit-mode, boot process and hardware initialization is much faster.
- User-Interface- The UEFI having a higher bit mode can have greater user interfaces and a mouse cursor too.
- Security- Authentication of boot drives to only allow secure boot drives to load. The system is already authenticated before running the OS.
- Network- network access before OS starts.
What are the criticisms of UEFI?
Security boot can create restricitons for people to have the operating system of their choice.
Additional complexity can create errors and attack vectors.
