AMD64 Architecture Programmer’s Manual. Volume 2: System Programming
www.amd.com/system/files/TechDocs/24593.pdf
1.1.2 Memory Organization
...
Physical Memory. Physical addresses are used to directly access main memory. For a particular computer system, the size of the available physical-address space is equal to the amount of main memory installed in the system. The maximum amount of physical memory accessible depends on the processor implementation and on the address-translation mode. The AMD64 architecture supports varying physical-memory sizes using the following address-translation modes:
• Real-Address Mode—This mode, also called real mode, supports 1 megabyte of physical-address space using 20-bit physical addresses. This address-translation mode is described in “Real Addressing” on page 10. Real mode is available only from legacy mode (see “Legacy Modes” on page 14).
• Legacy Protected Mode—This mode supports several different address-space sizes, depending on the translation mechanism used and whether extensions to those mechanisms are enabled. Legacy protected mode supports 4 gigabytes of physical-address space using 32-bit physical addresses. Both segment translation (see “Segmentation” on page 5) and page translation (see “Paging” on page 7) can be used to access the physical address space, when the processor is running in legacy protected mode. When the physical-address size extensions are enabled (see “Physical-Address Extensions (PAE) Bit” on page 121), the page-translation mechanism can be extended to support 52-bit physical addresses. 52-bit physical addresses allow up to 4 petabytes of physical-address space to be supported. (Currently, the AMD64 architecture supports 40-bit addresses in this mode, allowing up to 1 terabyte of physical-address space to be supported.
• Long Mode—This mode is unique to the AMD64 architecture. This mode supports up to 4 petabytes of physical-address space using 52-bit physical addresses. Long mode requires the use of page-translation and the physical-address size extensions (PAE).
Последнюю строку я даже выделю и повторю для самых внимательных:
«Long mode requires the use of page-translation and the physical-address size extensions (PAE)».
Про реальную разрядность адресации памяти реальных устройств сами ищите в текстах да читайте, мне для ленивых искать недосуг.
|
