When you start a new job it is not unnusual to be promised a raise at a later date depending on performance. This is the traditional carrot and stick scenario.
You're new at your job, probably on probation, and know you can be let go on a moment's notice.
Management tells you to work hard and you'll get a reward!
The sad truth is that more often than not the promise of a raise is just a platitude in order to inspire you to put in your best effort. If your 6 months are nearly over you may want to ask your manager whether you could sit down with him and ask for his opinion on your performance, and any advice he might have for you.
If he brings up a raise, then great. If he doesn't, that should tell you all you need to know.
Keep in mind that companies don't simply hand out raises willy nilly. If you're hired to do X, for $Y, and a year later you're still only doing X, then what is their motivation for paying you more? You're not bringing more value to the company.
However, if you do X really, really well, propose an improvement to the process, and have double the productivity of anyone else doing that same job, then you have a basis on which to ask for more money.
Keep all this in mind when you go speak to your manager. Raises are never implied, they're earned, and you have to prove that you've earned yours.