![where is it? where is it?](https://www.ladybirdeducation.co.uk/wp-content/uploads/2019/01/LR_SPT_WhereisitSpot_65472_WEB-pdf.jpg)
Then it checks for a specific sector in the defined first Boot device (typically Hard disk).
WHERE IS IT? PC
In term of Ubuntu system, the process is as following:Īfter you turn on your PC, BIOS (which is stored in ROM) automatically runs and initializes various parts of PC hardware. This tiny program in turn load a program from some where in the disk, which is called bootloader. In the first step a tiny program is loaded from a sector (called boot-sector more often) of Hard disk. Modern system use two stage boot loading.
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You should note that, generally Main Memory exclude memory of kinds as ROM. But yes, If you use Main Memory term for the entire memory space of a PC, then ROM is a part of that memory space. This is confusing, because typically Main Memory refers to the memory of kinds which are volatile, such as RAM. You mentioned that, You read an article where author said, "ROM is a part of Main memory". Where the program of very low level booting and initializing hardware are stored A typical example of ROM is BIOS chip.ROM are used to store permanent programs, which are very essential your hardware to perform correctly.These memory is non-volatile, in the sense, the program stored in ROM don't get erased with power shut down. More example, Your PC can consists of several ROM. It is a separate chip, which is most of the time built-in in a bigger IC. The EFI firmware used on Intel Macs and becoming available as a replacement to BIOS on most recent PC motherboards requires a dedicated partition that holds boot loader files, and the firmware is smart enough to find those files and load one instead of just loading and executing whatever is in the first sector of the disk.
WHERE IS IT? PLUS
The grub core image contains the base grub code, plus any modules needed to access /boot/grub so that it can load additional modules there, and the grub config file that describes what operating systems can be booted, and where they can be found. Normally a copy of this file is placed in the sectors following the MBR, but before the first partition, and that is actually what the MBR loads, since finding the location of /boot/grub/core.img is too difficult to do properly in the very limited space available in the MBR.
WHERE IS IT? CODE
Ubuntu uses the GRUB boot loader, which places enough code in the MBR to load and execute /boot/grub/core.img. By convention the first sector of a hard disk, called the Master Boot Record, contains a DOS partition table listing the locations of the partitions on the disk, and and leaves some space for the boot loader. With PC BIOS, it simply loads and executes the first sector off the disk it decides to boot from, which typically is the first hard disk detected. All firmware performs initialization of the hardware, typically provides some diagnostic output, and provides a way for the user to configure the hardware, then locates and loads the boot loader, which in turn locates and loads the OS.
WHERE IS IT? SOFTWARE
This is the software that the CPU first starts executing at power on. The motherboard has some type of ROM chip that holds the firmware, which in PC parlance is usually called the BIOS, or Basic Input Output System, though it is being replaced these days with EFI firmware.
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ROM generally is still used to refer to all of these types generically. These chips have a special software procedure to erase them so they can be reprogrammed. These were then replaced with EEPROM, or Electrically Erasable Programmable Memory. These chips had a little window on them and if you shined ultraviolet light into them, could be erased, allowing them to be programmed again. This was then replaced with EPROM, or Eraseable Programmable Memory. These chips came blank from the factory, and could be written to once using a special procedure that essentially burned out bits of the chip causing their state to change. Later PROM, or Programmable Read Only Memory replaced true ROM. It does not require power to retain its contents, and originally could not be modified by any means, but came hard wired from the factory.