How do OS installers works if there isn’t any OS that could manage applications in an empty computer?
In: Technology
You insert a boot medium (optical disk, USB drive, SD card, whatever) and tell the computer to load that OS during its UEFI/BIOS startup. It is loaded into memory and runs the computer from there. You then use that to install the permanent OS on the computer’s durable storage so you don’t need the boot medium every time.
A full OS isn’t needed to install the OS. The installer program contains the necessary code for the computer to comprehend.
You load an OS from a removable storage device. Today it is USB most of the time in the past CD/DVD or floppy disk was common.
You do need some initial software on a computer that is the EFI/BIOS on PC. So you have code stored in the motherboard that was put there when they are made. The information is simply written to the chip by another computer. In the past, they were ofter chips on sockets so you could switch them out by hand.
But you can also make the chip that contains the code as ROM where the data it the output depends on the physical structure of the chip. So the code is put there in the manufacturing process of the chip and ultimately by a human that designed the chip. History the masked used was made by drawing by hand and then shrunk down with optical methods. Stuff like woven rope core memory has also been used in the past as well as holes in papers. So it go back to information human put there.
All CPUs are designed to initially read a specific memory address and execute the instruction there. So you build the surrounding hardware to send the correct instruction.
So a computer will contain the initial code from the manufacture or can be attached to it.
There actually is something *kind of* like a very rudimentary OS built into an empty PC, called the BIOS. It’s stored on a permanent storage chip on the motherboard. The BIOS is the very first program the CPU starts executing once it’s powered up, and it only has a few jobs. Its main job is to scan the computer for internal hard drives or other storage media, and then look at the “boot sector” (a short block near the beginning) of those drives, to see if there’s any OS code there to run. If there is, then it loads and runs that code, and that’s how Windows or Linux or whatever starts running.
A computer has a thing called the BIOS built into its ROM. One of the jobs this has is to boot the machine–it can do this from the built-in hard drive, or a DVD-ROM, or USB key. Once it’s booted from one of those sources it turns over control to whatever code it just loaded and stays mostly out of the way.
So, the OS installer just has to be set up as something the BIOS can boot from and it will then run quite happily.
Once upon a time, in the early days of PCs when you might not even have a disc drive attached, the computer would boot into a ROM-resident version of the BASIC programming language if it didn’t find any other boot source, but they removed that a long time ago.
The BIOS doesn’t serve any more of a role during installation than it does any other boot.
The OS installer actually runs a slim version of the same OS it is installing, but loaded from the CD/DVD/thumb drive, instead of the hard drive.
After the excellent answers, it only remains to say that BIOS means Basic Input/Output System
There is a program that’s built into the computer itself called BIOS. When you turn on your computer it’s the BIOS’s job to load your operating system.
It can also load an OS from a disk or USB drive, which allows you to install them.
To explain it a different way, the installer itself acts as a temporary OS. The BIOS activates it and then it’s able to build a more permanent one.
Kinda like when they put up a construction crane, they build it as a small version, then use it to build itself up to full height.
You need that temporary small OS with no features other than the ones needs to install a bigger OS to make said larger OS happen.
Back in the old days you used to have to boot into a hard drive formatting tool to format it otherwise Windows didn’t know it existed.
When 2Gb disks arrived you had to tell it there was data that could exist
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