Debugger support is part of the operating system kernel. This allow reading memory belonging to another process. Debugger has the ability to identigy itslef as a debugger and its intent to debug other process. It has the ability to query and set values of debugger and debuggie's registers. To start debugger must be attaching to a certain process. Debugging allows Breakpoints which work on assembler level useing the INT 3 instruction. Debuggers mostly operate on CPU instruction level.