"Do you even own pants? Oh, wait. You do. I remember now." - Azriel
Q:

Dear 100 Hour Board,
I often like to type the word "okay" as I have just spelled it, but notice that people also just use "ok". Which one is more acceptable? I know the origin of O.K. so where did "okay" come from then?
-Grammar Nazi

A: Dear Grammar Nazi,

Well, first off, from what I can tell, it is preferable to use "okay" in formal writings while "OK" seems to be an abbreviation used in notes and personal writings. This is just from observation since I can't find a definitive rule.

Okay seems to be the phonetic spelling of OK. Thus, most places I find origins for okay, they are the same origins as for OK. You can browse through several of them for yourself.

http://www.miketodd.net/encyc/...
http://c2.com/cgi/wiki?Etymolo...
http://phrases.shu.ac.uk/meani...

Hope that helped.
- CGNU Grad