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. 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. 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.
ROM isn't a part of Main memory. It is a separate chip, which is most of the time built-in in a bigger IC. Those are built in your mother board. This is confusing, because typically Main Memory refers to the memory of kinds which are volatile, such as RAM. Modern system use two stage boot loading.
In the first step a tiny program is loaded from a sector called boot-sector more often of Hard disk. This tiny program in turn load a program from some where in the disk, which is called bootloader. And finally bootloader loads the OS. Then it checks for a specific sector in the defined first Boot device typically Hard disk. This sector is boot-sector, which is bytes in size. The program in the boot-sector is loaded in memory 1st stage. This tiny program has information which programs should it load into memory next and where that program is located in Disk or Boot device.
It loads that program. Then the kernel runs and loads all of the necessary programs such as display manager, Gui's etc. So, we can clearly say, that the bootloader is neither stored in ROM, nor in RAM, It is actually stored on Hard disk or other Boot device, such as bootable CDROM, USB drives etc , precisely speaking the first sector of the hard disk, which is of size bytes and often referred to as the boot-sector. And this bootloader loads the OS-loader in Ubuntu, it is grub which also resides in the hard disk i.
As a test, Remove the hard disk and all other boot device and try to boot. You can go up to the BIOS step, but after that step, you can't boot anything. An xcompatible processor always starts in so-called "real" mode, which is a bit mode with 1 megabyte of addressable memory available. From that address space, K are available for programs, and addresses above that are mapped to different devices. For example, addresses starting from 0xAx are mapped to the video RAM, so, writing data there would actually write data to the video adapter's memory displaying pixels on the screen.
From Wikipedia:. When the PC starts up, the first job for the BIOS is the power-on self-test, which initializes and identifies system devices such as the CPU, RAM, video display card, keyboard and mouse, hard disk drive, optical disc drive and other hardware. The BIOS firmware is responsible for reading the first sector from the disk into memory and passing the control to a small program which is, again, located at a specific address there.
Bootloaders which use the multi-stage approach can be quite complex with text or graphical interface which allows user to select from which disk or partition to load an operating system. So if, as Uri suggests, you're interested whether the Windows bootloader and GRUB can co exist together, the answer is: the actual MBR can only contain a single first-stage bootloader come on, the whole sector is just bytes , but the second stage of a bootloader may be able to "chain-load" operating systems from different partitions.
Windows bootloader is only able to recognize and load Windows, while GRUB is able to load Linux or pass control to another bootloader stored in a volume boot record of one of the partitions, which allows to boot Windows or other OS. The latter process is called chain-loading. The conflict between what you say about the bootloader being in ROM and it being in the MBR is perhaps due to bootloader being used for any code that works out how to do the minimum to load in code to make the computer do something useful, including each state in a multi-stage boot.
So, the starting state is to have a computer, which is a programmable device, but doesn't know how to load software to run because it doesn't have any software loaded.
And hence boot from pull itself up from its bootstraps. Historically, there were a few different solutions to this problem, but these days we start with some code in ROM mostly likely strictly EEPROM , which is enough to get it to look at different devices and try them in turn until it finds one that's bootable.
Incidentally, this explains why some OSes - like Windows - can only be installed on a primary partition, the details of those partitions are in the MBR and that's the only partition information their bootloader has read, and it doesn't load the EBR to learn about the logical partitions, as far as it's concerned those partitions don't even exist yet. That executable code, is also called a bootloader. When we care to distinguish between this and what comes next, it's called a primary boot loader because unless we're making our own BIOS we ignore the ROM bit as out of our control.
That code will be very small as there's only around bytes for it to fit in, so to do anything real, it will load some more code, that can be larger as it doesn't have to deal with this constraint. This code, is also known as a bootloader.
When we care to distinguish between this and what came before, it's called a secondary boot loader. That code could perhaps be the final stage in the process. It would if you've only one OS, or if all the OSs on your system use compatible boot-loaders e. In the case where you've an OS that isn't compatible with that bootloader, it may chainload. Google Green Messages. Use Your iPhone as a Webcam. Hide Private Photos on iPhone. All Microsoft's PowerToys for Windows.
Take Screenshot by Tapping Back of iPhone. Windows 11 Default Browser. Browse All Windows Articles. Windows 10 Annual Updates. OneDrive Windows 7 and 8. Copy and Paste Between Android and Windows. Protect Windows 10 From Internet Explorer.
Mozilla Fights Double Standard. Connect to a Hidden Wi-Fi Network. Change the Size of the Touch Keyboard. Reader Favorites Take Screenshot on Windows. Mount an ISO image in Windows. Boot Into Safe Mode. Where to Download Windows Legally. Find Your Lost Product Keys. Clean Install Windows 10 the Easy Way. Computer RAM is used only during operation. It's called "volatile memory", meaning that every time the computer is turned off, everything that has been stored on RAM is deleted.
Computer disk is a "non volatile" storage medium, meaning that programs and data will hopefully be available next time you turn on the computer.
RAM is necessary for normal operation of the computer. Programs and data that are essential to the immediate operations of the computer are loaded into RAM as the computer starts and when you start applications. Insufficient RAM may cause the computer to run very slow, if at all. Since nothing is stored on RAM when the computer is turned off, increasing the amount of RAM should not negatively affect any data that is currently stored on your computer.
Random access memory RAM is the machine's working memory. Start-up instructions - are stored on the computer's ROM chip. This performs a system check and loads the operating system into RAM. All other programs are usually stored on the computer's hard-drive - and loaded into RAM as, and when needed. Operating system is not stored in ROM. The software resides in the nonvolatile memory when it is not being run, and a copy is loaded into main memory when it is being run.
Log in. Computer Memory. Study now. See answer 1. Best Answer. In modern computers, programs are not stored on a ROM chip, but on the hard drive. Study guides. Computer Memory 21 cards. How many parts are there in the brain. REM sleep refers to. Perception is the ability to process information. What part of the brain processes visual information. Write your answer Related questions. Where are programs stored on a computer?
A place in the computer system where data and programs are temporarily stored?
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