PARTITION BASICS

It was common for early personal computers to have a single filesystem on their hard drives. Of course it was also common for their capacities to be measured in single digit megabytes. Once drives started becoming larger, people began organizing them into partitions.

Initially up to four partitions were available. When this was no longer enough, an ineloquent solution, known as extended partitions, was developed in order to allow more than four partitions to be created on a drive. People put up with this kludge for decades before a better solution was developed. All of these partitioning systems will be discussed in detail in this chapter starting with the oldest.

Hard drives are described by the number of read/write heads, cylinders, and sectors. Each platter has circles of data which are called tracks. When you stack multiple circles on top of each other they start to look like a cylinder and that is exactly what we call tracks that are on top of each other physically. Even when there is only one platter, there is a track on each side of the platter. The tracks are divided into chunks called sectors. Hard disk geometry is shown in Figure 5.1.

FIGURE 5.1

Hard disk geometry.

You will see entries for cylinders, heads, and sectors in some of the data structures discussed in this chapter. Most modern media use logical block addressing, but these remnants of an earlier time are still found. Whether or not these values are used is another story.