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For further information about PowerPC 64 bit processor, see PowerPC 64-bit Kernel Internals by David
Engebretson, Mike Corrigan & Peter Bergner at http://lwn.net/2001/features/OLS/pdf/pdf/ppc64.pdf. You
can find further in formation about System p hardware at
http://www-1.ibm.com/servers/eserver/pseries/linux/.
The following describes the four address types used in System p systems. They are effective, virtual,
physical, and block:
• Effective address: The effective address, also called the logical address, is a 64-bit address included
in the machine language instruction of a program to fetch an instruction, or to fetch and store data. It
consists of an effective segment ID (bits 0-35), a page offset within the segment (bits 36-51), and a
byte offset within the page (bits 52-63).
•
• Virtual address: The virtual address, which is equivalent to the linear address of System x, is a 64-bit
address used as an intermediate address while converting an effective address to a physical address.
It consists of a virtual segment ID (bits 0-35), a page offset within the segment (bits 36-51), and a
byte offset within the page (bits 52-63). All processes are given a unique set of virtual addresses.
This allows a single hardware page table to be used for all processes. Unique virtual addresses for
processes are computed by concatenating the effective segment ID (ESID) of the effective address
with a 23-bit field, which is the context number of a process. All processes are defined to have a
unique context number. The result is multiplied by a large constant and masked to produce a 36-bit
virtual segment ID (VSID). In case of kernel addresses, the high order nibble is used in place of the
context number of the process.
•
• Physical address: The physical address is a 64-bit address of a memory cell in a physical memory
chip.
• Block address: A block is a collection of contiguous effective addresses that map to contiguous
physical addresses. Block sizes vary from 128 KB to 256 MB. The block address is the effective
address of a block.
99
Figure 5-39: Effective address
Figure 5-40: Virtual address