Like Ryan said, most unis will do 3 modules in the first semester and three in the second. You still do the same amount of modules a year and receive the same amount of credits if you do joint or single. If you do joint you will do different modules to the single guys but may be in the same modules as them.
Example, I do single Linguistics. But I have course-mates doing Eng Lang & Linguistics. Therefore they are in two of my modules this semester, while I chose to be in one of theirs.