Explain stack structure of 8086

Answer 1

The stack in the 8086/8088 microprocessor, like that in many microprocessors, is a region of memory that can store information for later retrieval. It is called a stack, because you "stack" things on it. The philosophy is that you retrieve (pop) things in the opposite order of storing (push) them. In the 8086/8088, the stack pointer is SS:SP, which is a 16 bit pointer into a 20 bit address space. It, at any point of time, points to the last item pushed on the stack. If the stack is empty, it points to the highest address of the stack plus one. In a push operation, the SP register is decremented by two, and the data to be pushed is stored at that address, low order byte first. In a pop operation, the data to be popped is retrieved from that address, again low order byte first, and then the SP register is incremented by two. Some instructions, such as a FAR CALL, or FAR RETURN push or pop more than two bytes on the stack. It is also possible to allocate temporary storage on the stack. You simply decrement the SP register by some amount, use that memory, and then increment the SP register to release the memory. This is known as a stack frame. In fact, the BP register makes is very easy to do so. You use BP to separate arguments from local data - arguments will be above BP, and local data will be below BP. Memory reference instructions that are relative to BP, i.e. [BP+6] or [BP-48] will automatically use the SS segment register.

Answer 2

The stack in the 8085, and in many other stack oriented architectures, is a region of memory that can store and retrieve information in a last-in first-out paradigm. Primarily, the stack is used to store return addresses and register values for nested subroutine and interrupt calls.

The SP register, in the Intel architecture, points to the last item "pushed" onto the stack, or to the high end of the stack frame + 1 element for the case where the stack is empty. Pushing something on the stack involves decrementing the pointer and then storing the object at that memory location. (Well, sort of, but that's good enough for this discussion.) Popping something off of the stack involves reading the object from memory and then incrementing the pointer. Notice that decrement is second, but increment is first. This allows the stack to represent a nested structure of data.

Answer 3

The BIU in 8088 is 8-bit data bus & 16- bit in 8086.Instructionqueue is 4 byte long in 8088and 6 byte in 8086.