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Unformatted text preview: sing direct mapping (paging disabled), each linear address has a one-to-one correspondence with a physical address. Linear addresses are sent out on the processor's address lines without translation. When using the IA-32 architecture's paging mechanism (paging enabled), linear address space is divided into pages which are mapped to virtual memory. The pages of virtual memory are then mapped as needed into physical memory. When an operating system or executive uses paging, the paging mechanism is transparent to an application program. All that the application sees is linear address space. In addition, IA-32 architecture's paging mechanism includes extensions that support: Page Address Extensions (PAE) to address physical address space greater than 4 GBytes. Page Size Extensions (PSE) to map linear address to physical address in 4-MBytes pages. See also: Chapter 3, "Protected-Mode Memory Management," in the Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A. 3.3.3 Memory Organization in 64-Bit Mode Intel 64 architecture supports physical address space greater than 64 GBytes; the actual physical address size of IA-32 processors is implementation specific. In 64-bit mode, there is architectural support for 64-bit linear address space. However, processors supporting Intel 64 architecture may implement less than 64-bits (see Section 18.104.22.168). The linear address space is mapped into the processor physical address space through the PAE paging mechanism. 3.3.4 Modes of Operation vs. Memory Model When writing code for an IA-32 or Intel 64 processor, a programmer needs to know the operating mode the processor is going to be in when executing the code and the memory model being used. The relationship between operating modes and memory models is as follows: Protected mode -- When in protected mode, the processor can use any of the memory models described in this section. (The real-addressing mode memory model is ordinarily used only when the processor is in the virtual-8086 mode.) The memory model used depends on the design of the operating system or executive. When multitasking is implemented, individual tasks can use different memory models. 3-10 Vol. 1 BASIC EXECUTION ENVIRONMENT Real-address mode -- When in real-address mode, the processor only supports the real-address mode memory model. System management mode -- When in SMM, the processor switches to a separate address space, called the system management RAM (SMRAM). The memory model used to address bytes in this address space is similar to the realaddress mode model. See Chapter 24, "System Management," in the Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3B, for more information on the memory model used in SMM. Compatibility mode -- Software that needs to run in compatibility mode should observe the same memory model as those targeted to run in 32-bit protected mode. The effect of segmentation is the same as it is in 32-bit protected mode se...
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This note was uploaded on 10/01/2013 for the course CPE 103 taught by Professor Watlins during the Winter '11 term at Mississippi State.
- Winter '11