Buffers are often used in real time data operations to help allow for timing inconsistencies between the device supplying the data and the device requesting the data. However, there are limits to how much a buffer can… well… buffer. Its size and the data rate determine the limit. If the supply of data stops or slows down the buffer can only feed the destination device until it is empty. When it runs out of data a fault in the data will occur, the consequences of which depend upon the equipment in question. This fault is known as buffer under-run, which simply means the buffer was not able to supply data to the destination because it ran out of its supply. In the early days of CD burning this was a very common problem due to a combination of small (or no) buffers in the burners and slow disk access times, not to mention slower computers. Nowadays, CD burning technology has advanced to the point where buffer under-runs are fairly easily avoided; though they are not gone completely.