Data Protection and Security

VI

Operating System Security and Secure Programming

VI.II

Operating System Security

Modes of Operation:

Q: How to distinguish between OS operation and user operation?
A: A status flag can be used to this effect, allowing the system to work in different modes e.g. user mode and system (supervisor) mode.

• Motorola 68000 has one status bit and Intel 80386 has two status bits.
• These modes are useful. For instance, it becomes possible to stop users from writing directly to memory and corrupting the logical file structure.