http://serverfault.com/questions/85470/meaning-of-the-buffers-cache-line-in-the-output-of-freehttps://serverfault.com/questions/85470/meaning-of-the-buffers-cache-line-in-the-output-of-free
Short answer: the kernel uses the buffers/cache memory for various tasks, such as caching files. This memory is available to applications if it is needed, so you are correct in saying you have 944 MB used.