| Subject | English | Welsh |
| comp., MS | Microsoft Disk Operating System | System Weithredu Disg Microsoft (A Microsoft computer operating system with a command-line interface that is used to control many internal computer functions, such as running programs and organizing and maintaining files) |
| comp., MS | MS-DOS operating system | system weithredu MS-DOS (A Microsoft computer operating system with a command-line interface that is used to control many internal computer functions, such as running programs and organizing and maintaining files) |
| comp., MS | operating system | system weithredu (The software that controls the allocation and usage of hardware resources such as memory, central processing unit (CPU) time, disk space, and peripheral devices. The operating system is the foundation on which programs are built) |