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PENTIUM MEMORY MANAGEMENT The memory-management unit within the Pentium is upward-compatible with the 80386 and 80486 microprocessors. Many of the features of these earlier microprocessors are basically unchanged in the Pentium. The main change is in the paging unit and a new system memory- management mode. Paging Unit The paging mechanism functions with 4K-byte memory […]
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SPECIAL PENTIUM REGISTERS The Pentium is essentially the same microprocessor as the 80386 and 80486, except that some additional features and changes to the control register set have occurred. This section highlights the differences between the 80386 control register structure and the flag register. Control Registers Figure 18–8 shows the control register structure for the […]
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THE PENTIUM AND PENTIUM PRO MICROPROCESSORS INTRODUCTION The Pentium microprocessor signals an improvement to the architecture found in the 80486 microprocessor. The changes include an improved cache structure, a wider data bus width, a faster numeric coprocessor, a dual integer processor, and branch prediction logic. The cache has been reorganized to form two caches that […]
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QUESTIONS AND PROBLEMS 1. The 80386 microprocessor addresses bytes of memory in the protected mode. 2. The 80386 microprocessor addresses bytes of virtual memory through the memory-management unit. 3. Describe the differences between the 80386DX and the 80386SX. 4. Draw the memory map of the 80386 when operated in the (a) protected mode (b) real […]
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SUMMARY 1. The 80386 microprocessor is an enhanced version of the 80286 microprocessor and includes a memory-management unit that is enhanced to provide memory paging. The 80386 also includes 32-bit extended registers, and a 32-bit address and data bus. A scaled-down version of the 80386DX with a 16-bit data and 24-bit address bus is available […]
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THE MEMORY PAGING MECHANISM The paging mechanism allows any linear (logical) address, as it is generated by a program, to be placed into any physical memory page, as generated by the paging mechanism. A linear memory page is a page that is addressed with a selector and an offset in either the real or protected […]
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VIRTUAL 8086 MODE One special mode of operation not discussed thus far is the virtual 8086 mode. This special mode is designed so that multiple 8086 real-mode software applications can execute at one time. The PC operates in this mode for DOS applications using the DOS emulator cmd.exe (the command prompt). Figure 17–25 illustrates two […]
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MOVING TO PROTECTED MODE In order to change the operation of the 80386 from the real mode to the protected mode, several steps must be followed. Real mode operation is accessed after a hardware reset or by changing the PE bit to a logic 0 in CR0. Protected mode is accessed by placing a logic […]
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80386 MEMORY MANAGEMENT The memory-management unit (MMU) within the 80386 is similar to the MMU inside the 80286, except that the 80386 contains a paging unit not found in the 80286. The MMU performs the task of converting linear addresses, as they appear as outputs from a program, into physical addresses that access a physical […]
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THE 80386 AND 80486 MICROPROCESSORS INTRODUCTION The 80386 microprocessor is a full 32-bit version of the earlier 8086/80286 16-bit microprocessors, and represents a major advancement in the architecture—a switch from a 16-bit architecture to a 32-bit architecture. Along with this larger word size are many improvements and additional features. The 80386 microprocessor features multitasking, memory […]
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