What is the Difference between OEM and Boxed Versions of Various Computer Products ?

This Answer has Two Perspectives --

1. For Softwares : OEM Versions are generally meant to be bought when you buy / assemble a new PC. They are locked with the system you buy, later you cannot use the same software serial number with another PC even if you have removed it from the Previous PC. They are generally lesser Price wise, You are supposed to buy a Retail Box Product of the software if you are going to install it in an existing PC. Retail Version, You may, at your wish, Switch PC's as well, i.e., You may remove the software from one pc and install it on another. This is a generic answer, to give you an idea of the differentiation points in general. For the Correct definitions and terms .. You must refer to specific "terms of use document" of the software you intend to buy or install on the vendors website or from the media you get along.

2. For Hardware Products : OEM Versions are generally the same hardware but packed in bulk to reduce the packing and shipping cost by vendors. They are preferred if you are comfortable and understand what you are buying, sure of it's authenticity and have no doubt that the product is altered or fiddled with. There is no reason to buy a retail product when OEM is cheaper since you will be removing it's packaging and then installing it anyway. At the same time, if you doubt the originality of the product or if you do not trust the vendor, it is better that you go for Retail Box product only.