A further problem with bigger disks is the large amount of wasted space or “slack”. Since there are a fixed number of clusters available, larger disks mean that the cluster size has to be increased in order to fill the available space. However, this results in more and more unutilized disk space since a typical file is rarely close to an even multiple of a cluster size. For example, a FAT32 system uses 16 KB clusters for partition sizes between 16 and 32 GB. A 20 KB file would require two 16 KB clusters actually occupying 32 KB of space. A mere 1 KB file still requires 16 KB of space. A typical large disk might have 30% or even 40% of its space wasted this way. Making smaller partitions alleviates slack but with 200 GB disks now common, and ever-bigger ones on the way, partitioning is no longer a practical solution.
Another problem is file fragmentation. Although a file may require several clusters, the clusters need not be in close physical proximity on the disk. When a file is loaded to the disk the operating system chooses unused clusters wherever it finds them. If many files consist of widely separated parts, the time required to retrieve them for program use inevitably slows the system (hence the need for defragging).
It has to be remembered that the FAT system was first devised when the computer environment was very different from what it is today. Indeed, the PC as we know it did not even exist. FAT was intended for systems with very little RAM and small disks. It required much less in the way of system resources than did the file systems in Unix and other big computer systems and did its job well when systems were small. NTFS and Windows XP are practical for consumer PCs today only because the available resources of RAM and hard drive size have reached levels far exceeding anything imagined when FAT was first put into use.
Actually, the FAT system has been enjoying something of a come-back. Thumb or flash drives have become very common and these are of a size that makes the FAT system useful. The smaller sizes are even formatted in FAT16.