Beginner Mistakes

The idea to "write your own OS" brought you here. This Wiki is about giving you help, pointers, and references in your undertaking.

However, it is quite common that newcomers make certain mistakes, or have common misconceptions about what is involved in the topic. That is not bad - many others made these BeginnerMistakes before, and many will do so in the future. This page is about making sure you know what you're about, before digging into the provided information.

Scope

I have to write an OS for my studies, deadline is in three months...

The Linux kernel took over one year of very dedicated work to get into a semblance of usefulness, and all Linus Torvalds did was mimic existing and well-documented behaviour to get an already-existing userspace to run on it.

It took Linux almost a decade to really take off and attract a developer community.

And for every project as successful as Linux, there are literally hundreds of projects that consumed a man-year or more of work without ever getting as far as hosting a functional shell.

I will build a team of people...

Don't overestimate your chances of getting people interested in your project. Even the more successful projects of people usually consist of one, perhaps two people actually working on the code.

And that is not due to a lack of need.

Design

I have designed an OS, here's a picture...

It will likely take you several years, starting from scratch, to get to the point where you actually do anything GUI-related. And, the looks of a GUI are secondary at best, as they can easily be changed retroactively; what really decides the usability of a GUI is the functionality, and that isn't expressed in mock-up graphics. If your aim is creating a better look instead of a better OS, consider implementing an X Window Manager instead of a whole OS.

My OS will emulate Mac OS, Windows, Linux, and every other OS out there!

I'm sorry to burst your bubble, but it probably won't. Emulating even just a single system takes years of work, especially when it's proprietary, such as Windows or Mac OS. (Linux is probably the easiest out of the three.) So instead of focusing on emulating other systems focus on your own. Design it, develop it, be friends with it.

Also, don't get your mind set that by building such a great OS that you'll be rich. If anything, history has shown us that the best operating systems never receive any commercial success, while the ones that have a near total lack of design and inspiration do.

I have cool ideas, but i need a cool name for it.

Naming is usually the last problem to be solved, even while we all wish for a cool name to our cool concept. Since the "coolness" of a name is a matter of taste, we cannot help you finding it. Moreover, if you tie your project name to a certain feature, you might discover somewhere down the road that no concept is perfect and that you might want to change what you initially thought a key feature. Nothing would be more stupid not to evolve just because you 'want to stick to a name'...

I want to write an OS in QBasic...

Some languages are well suited to write an OS kernel, others are less so. Read the page about using some language other than C.

Kernel Image

I have successfully loaded my kernel. It works as long as it doesn't exceed XXX bytes. My Kernel got bigger, and now I keep getting exceptions and faults. Why?

Especially in early stages and with a self-built boot loader, the reason is frequently that too few sectors are fetched from disk. Either adjust the amount of sectors you fetch from disk, or have the boot loader / second stage loader parse the file system.

When I use strings in my Kernel, it doesn't work/crashes/has a corrupt Multiboot-Header

When your Kernel is written in C, gcc puts strings and constants in a special section called "read-only data". This section needs to be in your linkscript, in the =.text= section, otherwise it can cause all sorts of weird problems (unable to print text to the screen, kernel suddenly becoming 1MB larger, GRUB giving a loading error saying "kernel too large", etc). The section is called ".rodata" in ELF and ".rdata" in COFF/PE (the output format for MinGW/Cygwin). Building a [GCC Cross-Compiler] will help you to safely assume ".rodata" everywhere.

You could also tweak your linker script to include either section:

...
.text 0x100000 {
  *(.text)
  *(.rodata*) /* <---- ELF Cross Compiler or ELF *NIX (eg. Linux) */
  *(.rdata*)  /* <---- COFF/PE MinGW or Cygwin on Windows */
}
  ...