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My ideas are constantly changing as I learn. Sometimes they even change midway through writing a post.

Friday, September 16

Booting up

Boot is actually shorthand for "bootstrap" which is the original term. Obviously, a computer is just a hunk of iron until a program starts. Early computers, in the days before microcode and eprom, etc., had a "load" button, like the button on your PC or Mac that restarts it. The hardware action taken when the Load button was pressed was to transfer X bytes of data from a specific location on a specific disk volume into memory at location zero and then fetch the instruction at location zero and execute it. This instruction caused more data to be read into memory and the process continued until the system had pulled itself up by the bootstraps. A dual loader is simply adding a prefix to this process which lets you decide where to go to start the real bootstrapping.

I appreciate the extra information. I had this nagging feeling when I posted yesterday, that there was something missing in the explanation about a loader. It wasn't until I was talking over this idea of what a "loader" was with a friend, and he said that it wasn't the first thing that ran on a computer that I realized what it was.

I thought the system test thing (POST) was the first program to run(at least on a PC). Warning: Thing and thingy are terms I commonly use for things I can't remember the name of although I actually did remember the name this time. I looked on Wikipedia and it says that the last part of POST is the boot loader. And technically, the definition on the Gnu page said "software".

I don't know that however the BIOS and POST work is "software" or considered some other thing. Can there be hardware or firmware programs? (I learned these terms so long ago that not only is it difficult to remember, even correct memories might not be true anymore).

Anyway, it seems there are several steps before the operating system gets loaded. I suppose there could be some disagreement on the meaning of operating system.

One other little correction to the bit about Grub. Grub is apparently a second stage boot loader.

1 comment:

gon4good said...

You are absolutely right on two counts; Power On Self Test occurs at the hardware level before the bootstrap code is fetched. And in the case of a PC, most of the time, there is no Operating System at all, simply some half-baked crap from the Pacific northwest.