CPU Modes and Memory Models

Question 1

Real Mode

Answer 1

Happens at power up or reset. 1 MB of addressable memory, no memory protection, no privilege levels.

Question 2

Protected Mode

Answer 2

Main mode. 4 GB of addressable memory on 32 bit. Memory protection, privilege levels, and multitasking. Supports virtual 8086 mode.

Question 3

System Management Mode

Answer 3

Used for power management tasks.

Question 4

Flat Memory Model

Answer 4

Linear address space. IA-32 Linux uses this. Segment registers point to segment descriptors GDT/LDT/IDT.

Question 5

Segmented Memory Model

Answer 5

Specific memory location addressed with segment selector and offset within segment.

Question 6

Real-Address Mode Memory Model

Answer 6

Special case of segmented memory model with equal segment sizes.

Question 7

Virtual Memory Model

Answer 7

1 GB kernel, 3 GB user space (approx). From kernel space downward the segments are stack, shared libs & mappings, heap, BSS (unitialized data), data (initialized data), and text.