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• To access a particular memory location, the CPU transforms an effective address into a physical
address using one of the following address translation mechanisms.
• Real mode address translation, where address translation is disabled. The physical address is the
same as the effective address.
• Block address translation, which translates the effective address corresponding to a block of 128 KB
to 256 MB size.
• Page address translation, which translates a page-frame effective address corresponding to a 4-Kbyte
page.
The translation mechanism is chosen based on the type of effective address (page or block) and settings in the
processor Machine State Register (MSR).
Settings in the MSR and page, segment, and block descriptors are used in implementing access control. The
following describes the MSR, page descriptor, segment descriptor, and block descriptor structures, and
identifies fields that are relevant for implementing access control.
5.5.2.3.1 Machine State Register
The Machine State Register (MSR) is a 64-bit register. The MSR defines the state of the processor.
• PR: Privilege Level. The Privilege Level takes the value of 0 for the supervisor level and 1 for the
user level.
• IR: Instruction Address Translation. The value of 0 disables translation, and the value of 1 enables
translation.
100
Figure 5-41: Block address
Figure 5-42: Machine state register