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Page Numbers and Offsets
IRIX manages memory in units of a page. The size of a page can differ from one system to another. The size when 32-bit addressing is used is 4,096 bytes. In each 32-bit virtual address,
- the least-significant 12 bits specify an offset from 0 to 0x0fff within a page
- the most-significant 20 bits specify a virtual page number (VPN)
The page size when 64-bit addressing is used is greater than 4,096 bytes (and can differ between versions of IRIX), but the principle is the same. The less-significant bits of an address specify an offset within a page, while the more-significant bits specify the VPN.
The actual size of a page in the present system can be learned with getpagesize() as noted under "Interrogating the Memory System".
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