I am thy DOS, thou shall have no OS before me, unless Bill Gates gets a cut of the profits therefrom.
Thy DOS is a character based, single user, single tasking, standalone operating system. Thou shall not attempt to make DOS network,multitask, or display a graphical user interface, for that would be a gross hack.
Thy hard disk shall never have more than 1024 sectors. You don’t need that much space anyway.
Thy application program and data shall all fit in 640K of RAM. After all, it’s ten times what you had on a CP/M machine. Keep holy this 640K of RAM, and clutter it not with device drivers, memory managers, or other things that might make thy computer useful.
Thou shall use the one true slash character to separate thy directory path. Thou shall learn and love this character, even though it appears on no typewriter keyboard, and is unfamiliar. Standardization on where that character is located on a computer keyboard is right out.
Thou shall edit and shuffle the sacred lines of CONFIG.SYS and AUTOEXEC.BAT until DOS functions adequately for the likes of you. Giving up in disgust is not allowed.
Know in thy heart that DOS shall always maintain backward compatibility to the holy 2.0 version, blindly ignoring opportunities to become compatible with things created in the latter half of this century. But you can still run WordStar 1.0.
Improve thy memory, for thou shall be required to remember that JD031792.LTR is the letter that you wrote to Jane Doe four years ago regarding the tax deductible contribution that you made to her organization. The IRS Auditor shall be impressed by thy memory as he stands over you demanding proof.
Pick carefully the names of thy directories, for renaming them shall be mighty difficult. While you’re at it, don’t try to relocate branches of the directory tree, either.
Learn well the Vulcan Nerve Pinch (ctrl-alt-del) for it shall be thy saviour on many an occasion. Believe in thy heart that everyone reboots their OS to solve problems that shouldn’t occur in the first place.