The Intel Microprocessors

Real Mode Memory Addressing Real mode, also called real address mode, is an operating mode of and later x86-compatible CPUs. Real mode is characterized by a 20 bit segmented memory address space (giving exactly 1 MB of addressable memory) and unlimited direct software access to all memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels

Real Mode Memory Addressing Segment and offsets Segment address located in one of the segment registers defines the beginning address of any 64K memory segments. Offset address selects any location within the 64K memory segments. Offset sometimes referred to as displacement. Ending address is found by adding FFFFH with the beginning address.

Default Segment and Offset Registers CS:IP Instruction Address SS: SP or BP(base pointer) Stack Address DS: BX, DI Data address. ES :DI String destination address.

Protected Mode Memory Addressing In computing, protected mode, also called protected virtual address mode, is an operational mode of x86- compatible central processing units (CPU). It allows system software to utilize features such as virtual memory, paging, safe multi-tasking, and other features designed to increase an operating system's control over application software.

Protected Mode Memory Addressing Descriptor describes the location, length and access rights of the segment of memory. Segment register contains a selector that selects a descriptor from a descriptor table.

There are two descriptor tables used with segment registers. Global Descriptor(System descriptor): Contain segment definitions that apply to all programs. Local Descriptors(application descriptor): Unique to an application.

Base address: Indicates the starting location of the memory segment. Segment Limit: Contains the last offset address found in a segment.

9 Page Tables Internal operation of MMU with 16 4 KB pages