(v) To divide memory or mass storage into isolated sections. In DOS systems, you can partition a disk, and each partition will behave like a separate disk drive. Partitioning is particularly useful if you run more than one operating system. For example, you might reserve one partition for Windows and another for UNIX.
In addition, partitioning on DOS and Windows machines can improve disk efficiency. This is because the FAT system used by these operating systems automatically assigns cluster size based on the disk size: the larger the disk, the larger the cluster. Unfortunately, large clusters can result in a wasted disk space, called slack space. There is an entire sector of the software industry devoted to building utilities that let you partition your hard disk.
On Apple Macintosh computers, there are two types of partitioning: hard and soft. Hard partitioning is the same as DOS partitioning -- the disk is physically divided into different sections. Soft partitioning, on the other hand, does not physically affect the disk at all, but it fools the Finder into believing that the disk is partitioned. The advantage of this is that you can partition the disk without affecting the data on it. With hard partitioning, it is usually necessary to reformat the entire disk.