Page Table Entries

The page directory entries are identical to the page table entries.

Each entry is 4 bytes, making 1K entries in each page table.

Bits 31-12

Physical Address of page, or Page Frame Address
Bits 11-09
Ignored by hardware, used by OS2. See Note.
Bits 08-07
Reserved, must be zero
Bit 6
Dirty (D) 0=not changed (clean), 1=changed (dirty)
Bit 5
Accessed (A) 0=not accessed, 1=accessed
Bit 4
Page Cache Disable 0=allow cache use, 1=bypass cache
Bit 3
Page Write-Through 0=cache write-into, 1=write through to RAM
Bit 2
Supervisor (S/U) 0=Supervisor (PL=0,1,2), 1=user (PL=3)
Bit 1
Write enable (RO/RW) 0=Read Only, 1=Read/Write
Bit 0
Present (P) 0=not present, 1=present

Note: The left 5 hex digits of the entry are the left 5 hex digits of the physical page; while the right 3 hex digits are mostly flags.

Note: If Bit 0 is zero, ( page invalid ) the remaining bits are NOT inspected by the hardware. OS/2 uses them to identify the virtual page associated with this address.

Note: Bits 09 and 10 are used to track the state of the page frame. Three of the possible four combinations are used:

• Pageable

• UVirt

• Resident

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