3. Describe each of the three categories of operating systems.

Sure, there are three categories of operating systems:

1. Single-user single-tasking operating system - This type of operating system only allows one user to work on one task at a time. Examples of such operating systems include MS-DOS and older versions of Mac OS.

2. Single-user multi-tasking operating system - This type of operating system allows a single user to work on multiple tasks simultaneously. The tasks are executed one at a time by the CPU, and the operating system switches between them using a scheduling algorithm. Examples of such operating systems include Windows, macOS, and Linux.

3. Multi-user operating system - This type of operating system allows multiple users to use the computer simultaneously. It provides features like access control and resource sharing, allowing users to access files, data, and other resources owned by other users. Examples of such operating systems include Unix, Linux, and mainframe OS like IBM's z/OS.