Segment registers are called selectors when operating in protected mode. In protected mode, segment registers simply point to data structures called segment descriptors that contain the information needed to access a physical memory location.
What is the purpose of segment registers?
A segment register changes the memory address accessed by 16 bits at a time, because its value is shifted left by 4 bits (or multiplied by 16) to cover the entire 20-bit address space. The segment register value is added to the addressing register’s 16-bit value to produce the actual 20-bit memory address.
What is segment register in a computer?
Segment registers are basically memory pointers located inside the CPU. Segment registers point to a place in memory where one of the following things begin: Data storage. Code execution.
What is the use of code segment register in 8086?
8086 Segment Registers
These registers are all 16 bits wide. They deal with selecting blocks (segments) of main memory. A segment reg- ister (e.g., cs) points at the beginning of a segment in memory. Segments of memory on the 8086 can be no larger than 65,536 bytes long.
What is the purpose of IP register?
A special-purpose register, usually called the instruction pointer (IP) or program counter (PC), keeps track of what instruction is being executed.
Why extra segment is used?
The es (Extra Segment) register is an extra segment register. 8086 programs often use this segment register to gain access to segments when it is difficult or impossible to modify the other segment registers. The ss (Stack Segment) register points at the segment containing the 8086 stack.
What is difference between real and protected mode?
The major difference between 80386 Real and Protected mode is the way that segment selectors are interpreted. When the processor is operating in Virtual Mode the segment registers are used in an identical to Real Mode.
|Real Mode||Protected Mode (PVAM)|
|No virtual memory support||Supports up tp to 64TB of virtual memory|
Are segment registers still used?
Every process access its own memory (4GB) in linear fashion, so basically the segment registers are not needed. They are still registers, so they can of course be used for various other assembly operations. FS points to the exception handling chain, CS and DS are filled from the OS with code and data segment.
What is the use of SI register?
SI – This is the source index register. It is of 16 bits. It is used in the pointer addressing of data and as a source in some string related operations. It’s offset is relative to data segment.
What do you mean by segment?
Definition of segment
(Entry 1 of 2) 1 : a portion cut off from a geometric figure by one or more points, lines, or planes: such as. a : the area of a circle bounded by a chord and an arc of that circle. b : the part of a sphere cut off by a plane or included between two parallel planes.
What are the three aspects of segments in memory?
- Data segment − It is represented by . data section and the . bss. The . …
- Code segment − It is represented by . text section. This defines an area in memory that stores the instruction codes. …
- Stack − This segment contains data values passed to functions and procedures within the program.
What is the difference between segment register and general purpose register?
Segments are specific areas clear in a program for containing data, code and stack. There are 3 main segments − Code Segment − It contains all the instructions to be executed. A 16-bit Code Segment register or CS register supplies the starting address of the code segment.
Which of the following is the segment register?
Explanation: The segment descriptor register is used to store the descriptor information like attributes, limit and base addresses of segments. Sanfoundry Global Education & Learning Series – Microprocessors.