2--x86 Processor

It runs on a processor that supports task switching

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Unformatted text preview: hile a computer program is running. A bus is a series of parallel wires that transmit data among various parts of the computer. The execution of a single machine instruction can be divided into a sequence of individual operations called the instruction execution cycle. The three primary operations are fetch, decode, and execute. Each step in the instruction cycle takes at least one tick of the system clock, called a clock cycle. The load and execute sequence describes how a program is located by the operating system, loaded into memory, and executed by the operating system. A multitasking operating system can run multiple tasks at the same time. It runs on a processor that supports task switching, the ability to save the current task state and transfer control to a different task. x86 processors have three basic modes of operation: protected mode, real-address mode, and system management mode. In addition, virtual-8086 mode is a special case of protected mode. For More BS-IT Books, Notes & Assignments visit: www.bsit.zxq.net 56 Chapter 2 • x86 Downloaded From: www.bsit.zxq.net Processor Architecture Intel64 processors have two basic modes of operation: Compatibility mode and 64-bit mode. In Compatibility mode they can run 16-bit and 32-bit applications. Registers are named locations within the CPU that can be accessed much more quickly than conventional memory. Following are brief descriptions of register types: • The general-purpose registers are primarily used for arithmetic, data movement, and logical operations. • The segment registers are used as base locations for preassigned memory areas called segments. • The EIP (instruction pointer) register contains the address of the next instruction to be executed. • The EFLAGS (extended flags) register consists of individual binary bits that control the operation of the CPU and reflect the outcome of ALU operations. The x86 has a floating-point unit (FPU) expressly used for the execution of high-speed floatingpoint instructions. The Intel 8086 processo...
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