A Brief Overview of the Evolution of Partitioning: From A: and B: to the Prevalent Use of C: as the System Partition


Over the years, computer systems have undergone significant transformations, including changes in data storage and partitioning. In the early days of personal computing, the A: and B: partitions were commonplace, primarily used for floppy disk drives. However, with the advent of modern systems, particularly hard drives, the usage and significance of these partitions have evolved. Today, the C: partition is predominantly allocated as the system partition, and this article aims to explore the reasons behind this transition and the benefits it brings.

A: and B: Partitions: A Nostalgic Throwback

In the early days of computing, floppy disk drives were the primary means of data storage. These drives were commonly assigned the drive letters A: and B: to differentiate them from the primary hard drive (if present), which typically received the letter C:. The A: partition was usually reserved for the primary floppy drive while the B: partition designated an additional floppy drive if one was connected. In those days, although HDDs existed they were barely used due to their hefty price. However, technological advancements largely reduced the price of HDDs and rendered these partitions largely obsolete, and the need for C: as the system partition arose. It is interesting to note that the pre-Microsoft DOS version initially didn't even support hard drives, they will gain this support after Microsoft's acquisition with MS-DOS 2.0.

The Rise of Hard Drives and C: as the System Partition

With the reduction of cost and increasing popularity and capacities of hard drives, the role of partitions expanded. The C: partition became the default system partition to store the operating system and other essential files required for the proper functioning of the computer. This shift was driven by several factors, including convenience, familiarity, and compatibility. With MS-DOS 5.0 the C: partition is always assigned to the hard drive.

Benefits and Reasons for Using C: as the System Partition

• Convenience: By designating the C: partition as the system partition, users can benefit from a streamlined experience. The operating system automatically boots from this primary partition, simplifying the implementation and usage of various software and applications.

• Familiarity: The extensive usage of C: as the system partition has created a widespread familiarity among users. This standardization allows for easier troubleshooting, support, and software development, as most configurations and software installations assume a C: system partition.

• Compatibility: Many legacy applications and utilities, both commercial and open source, have hardcoded references to the C: drive. These references assume that the operating system resides on the C: partition. Deviating from this convention may lead to compatibility issues, rendering some software inoperable or requiring manual adjustments, thus increasing complexity.

Alternative Uses for A: and B: Partitions

While A: and B: partitions are largely considered outdated for hard drives, they still serve a purpose in some niche scenarios. For instance, in systems with multiple physical disks or when using external storage devices, these partitions can be allocated to different drives, enabling faster data transfers or easy access to specific files. However, for most average users, the C: partition remains the optimal choice as the system partition.


From the nostalgia-inducing A: and B: partitions used in the early days of personal computing to the modern dominance of the C: partition as the system partition, the world of computer partitioning has undergone significant changes. The shift to C: as the system partition has brought with it numerous benefits, including convenience, familiarity, and compatibility. By understanding this evolution, users can better appreciate the reasons behind this transition and make informed decisions regarding their computer systems.