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The 8086 [3] (also called iAPX 86) [4] is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, [5] is a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting ICs), [note 1] and is notable as the processor used in the original IBM PC design.
32-bit interrupt return. Differs from the older 16-bit IRET instruction in that it will pop interrupt return items (EIP,CS,EFLAGS; also ESP [j] and SS if there is a CPL change; and also ES,DS,FS,GS if returning to virtual 8086 mode) off the stack as 32-bit items instead of 16-bit items.
In real mode, code may also modify the CS register by making a far jump (or using an undocumented POP CS instruction on the 8086 or 8088). [4] Of course, in real mode, there are no privilege levels; all programs have absolute unchecked access to all of memory and all CPU instructions.
x86 (also known as 80x86 [3] or the 8086 family [4]) is a family of complex instruction set computer (CISC) instruction set architectures [a] initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088.
In 8086, the main stack register is called "stack pointer" (SP).The stack segment register (SS) is usually used to store information about the memory segment that stores the call stack of currently executed program.
To use virtual 8086 mode, an operating system sets up a virtual 8086 mode monitor, which is a program that manages the real-mode program and emulates or filters access to system hardware and software resources. The monitor must run at privilege level 0 and in protected mode. Only the 8086 program runs in VM86 mode and at privilege level 3.
The Intel 8086 trap flag and type-1 interrupt response make it quite easy to implement a single-step feature in an 8086-based system. If the trap flag is set, the 8086 will automatically do a type-1 interrupt after each instruction executes. When the 8086 does a type-1 interrupt, it pushes the flag register on the stack.
8086 first x86 processor; initially a temporary substitute for the iAPX 432 to compete with Motorola, Zilog, and National Semiconductor and to top the successful Z80. The 8088 version, with an 8-bit bus, was used in the original IBM Personal Computer. 186 included a DMA controller, interrupt controller, timers, and chip select logic. A small ...