A major problem in model-checking timed systems is the<br />huge memory requirement. In this paper, we study the memory-block<br />traversal problems of using standard operating systems in exploring the<br />state-space of timed automata. We report a case study which demonstrates<br />that deallocating memory blocks (i.e. memory-block traversal)<br />using standard memory management routines is extremely time-consuming.<br />The phenomenon is demonstrated in a number of experiments by<br />installing the Uppaal tool on Windows95, SunOS 5 and Linux. It seems<br />that the problem should be solved by implementing a memory manager<br />for the model-checker, which is a troublesome task as it is involved in<br />the underlining hardware and operating system. We present an alternative<br />technique that allows the model-checker to control the memory-block<br />traversal strategies of the operating systems without implementing<br />an independent memory manager. The technique is implemented in the<br />Uppaal model-checker. Our experiments demonstrate that it results in<br />significant improvement on the performance of Uppaal. For example, it<br />reduces the memory deallocation time in checking a start-up synchronisation<br />protocol on Linux from 7 days to about 1 hour. We show that the<br />technique can also be applied in speeding up re-traversals of explored<br />state-space.