![]() It does this by going around and interrogating various devices until it finds one that can boot. It's literally the first code that runs when your computer is turned on.Īfter BIOS has performed its work and initialized the hardware it needs to initialize, it starts to look for the OS to boot. When your computer is turned on, the motherboard loads this code in RAM and then sets the CPU to start executing it. BIOS is a bunch of code that is stored in a special chip on your motherboard (you can update this code with "BIOS updates" from your motherboard manufacturer). If anyone can correct errors in my text, I'd be happy!įirstly, BIOS and bootloader aren't the same thing. My own understanding of these things is a bit rough as well, but hopefully I'll be able to shed a little light that will enable you to continue on your path. what thing defines the number 0xaa55 magic number should be 0xaa55. like if someone makes own bootloader or edit grub code then one can consider any number as magic number let say 0xabcd. I like know how OS starting address is found if there are multiple OSes and single disk with multiple partitionsĪlso is 0xaa55 considering without partitions on same disk is it same for all CPU architectures(is 0xaa55 is magic number for both x86 and x86-64) and hard disks dependent? Or it a bios or bootloader dependent. The above led me to think that magic number may be one for every disk but not anymore after concept of disk partition there may be some other number too. Cylinder 0, Head 0, Sector 0),Īn unsophisticated means is adopted here by BIOS, whereby the last twoīytes of an intended boot sector must be set to the magic number 0xaa55 The author says So, the easiest place for BIOS to find our OS is in the first sector of one of theĭisks (i.e. Since I can make partition ,divided the disk into multiple parts let say Linux-A and Linux-B partitions. as the boot sector magic number location for only disk is taken by first OS magic number: present at Cylinder 0, Head 0, Sector 0. where the magic number stored of second OS if I only had one hardware disk device but multiple partitions. ![]() so let say I have two or three OS installed and at boot option I can select which one to boot from. So it means that its written in the hard disk(s). ![]() from the tutorial I read that The way bootloader/bios (these two terms are used interchangbly by the writer I think) differentiates to find executable of OS and data and things is by using loop and check for a thing called magic number which is stored once in every disk at specific address location. Which lead to a lengthy tutorial from a university professor. I was trying to study bootloader and OS and bios do.
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