Note: This API calls are shared between DOS and Win16 personality.

DPMI is a shared interface for DOS applications to access Intel 80286+ CPUs services. DOS DMPI host provides core services for protected mode applications. Multitasking OS with DOS support also provides DMPI in most cases. Windows standard and extended mode kernel is a DPMI client app. Standard and extended mode kernel differs minimally and shares common codebase. Standard Windows kernel works under DOSX extender. DOSX is a specialized version of 16-bit DPMI Extender (but it is standard DPMI host). Standard mode is just DPMI client, exnhanced mode is DPMI client running under Virtual Machime Manager (really, multitasker which allow to run many DOS sessions). Both modes shares DPMI interface for kernel communication. The OS/2 virtual DOS Protected Mode Interface (VDPMI) device driver provides Version 0.9 DPMI support for virtual DOS machines. Win16 (up to Windows ME) provides Version 0.9 DPMI support.

DPMI host often merged with DPMI extender. Usually DPMI extender provide DPMI host standard services and DOS translation or True DPMI services.

2021/08/05 12:15 · prokushev

Int 31H, AH=05H, AL=07H




Set Page Attributes


AX = 0507H
ESI = memory block handle
EBX = offset within memory block of page(s) whose attributes are to be modified
ECX = number of pages
ES:EDX = selector:offset of a buffer containing page attributes, 1 word (16-bits) per page (see Note)


if function successful
Carry flag = clear

if function unsuccessful
Carry flag = set
AX = error code
8001H	unsupported function (16-bit host)
8002H	invalid state (page in wrong state for request)
8013H	physical memory unavailable
8014H	backing store unavailable
8021H	invalid value (illegal request in bits 0-2 of one or more page attribute words)
8023H	invalid handle (in ESI)
8025H	invalid linear address (specified range is not within specified block)
ECX = number of pages that have been set


Sets the attributes of one or more pages within a linear memory block previously allocated with Int 31H Function 0504H. This function can be used to change a committed page or a mapped page to an uncommitted page, change an uncommitted page or a mapped page to a committed page, or modify the read/write bit and optionally the accessed and dirty bits on a committed or mapped page.

A DPMI 1.0 host that is 16-bit only will not support this function.

A 16-bit client of a 32-bit DPMI 1.0 host can use this function.

If EBX is not aligned, it will be rounded down to the next lower page boundary.

An uncommitted page can be created from:

  a committed page, by releasing the physical memory or backing store allocated to the page;
  a mapped page, by marking it uncommitted; or an uncommitted page, by doing nothing. 

A committed page can be created from:

  an uncommitted page or mapped page, by allocating physical memory or backing store (with undefined, or zero-filled contents) for the page; or
  a committed page, by doing nothing (page contents unmodified). 

The attribute word (16-bits) specified for a page has the following format (bits 3-6 are only relevant if page is being created committed or its attributes are being modified, i.e. the value in bits 0-2 of the page attribute is 1 or 3):

Bits Significance
0-2 page type (0-7)
Value Meaning
0 create page uncommitted
1 create page committed
2 not allowed
3 modify attributes without changing page type
4-7 not allowed
3 0 = page is read-only 1 = page is read/write
4 0 = don't modify accessed/dirty bits for page 1 = set accessed/dirty bits as specified in bits 5-6
5 0 = mark page as not accessed (if bit 4=1) 1 = mark page as accessed (if bit 4=1)
6 0 = mark page as not dirty (if bit 4=1) 1 = mark page as dirty (if bit 4=1)
7-15 reserved, should be zero

This function, and the optional Map Device and Map Conventional Memory functions (Int 31H Functions 0508H and 0509H), are the only means of changing the type of a page within an existing memory block.

The page read/write bit, and optionally the accessed and dirty bits, can be modified on an existing committed or mapped page, or on a committed page when it is initially created from an uncommitted page or a mapped page. However, the accessed and dirty bits are ignored if the host does not support the Page Accessed/Dirty capability. See Int 31H Function 0401H.

Visible page faults (page faults that can be serviced by a client-installed exception handler) can only occur for uncommitted pages or read-only pages (for definitions of transparent page fault and visible page fault, see Appendix A: Glossary).

See also


Process manager INT 2FH 1680H, 1687H
Memory manager
Misc INT 2FH 1686H, 168AH
2021/08/13 16:23 · prokushev

en/docs/dpmi/api/int31/05/07.txt · Last modified: 2021/08/27 06:56 by prokushev