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 <TITLE>INT 15h, AX=E820h - Query System Address Map</TITLE>
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 <H1>INT 15h, AX=E820h - Query System Address Map</H1>
 <HR>

 Real mode only.<P>

 This call returns a memory map of all the installed RAM, and of physical
 memory ranges reserved by the BIOS.  The address map is returned by making
 successive calls to this API, each returning one "run" of physical address
 information.  Each run has a type which dictates how this run of physical
 address range should be treated by the operating system.<P>

 If the information returned from INT 15h, AX=E820h in some way differs from
 <A HREF="#int15e801">INT 15h, AX=E801h</A> or
 <A HREF="#int1588">INT 15h AH=88h</A>,
 then the information returned from E820h
 supersedes what is returned from these older interfaces.
 This allows the BIOS
 to return whatever information it wishes to for compatibility reasons.<P>

 <HR>

 Input:<P>

 <pre>
 	EAX	Function Code	E820h
 	EBX	Continuation	Contains the "continuation value" to get the
 				next run of physical memory.  This is the
 				value returned by a previous call to this
 				routine.  If this is the first call, EBX
 				must contain zero.
 	ES:DI	Buffer Pointer	Pointer to an  Address Range Descriptor
 				structure which the BIOS is to fill in.
 	ECX	Buffer Size	The length in bytes of the structure passed
 				to the BIOS.  The BIOS will fill in at most
 				ECX bytes of the structure or however much
 				of the structure the BIOS implements.  The
 				minimum size which must be supported by both
 				the BIOS and the caller is 20 bytes.  Future
 				implementations may extend this structure.
 	EDX	Signature	'SMAP' -  Used by the BIOS to verify the
 				caller is requesting the system map
 				information to be returned in ES:DI.
 </pre>

 Output:<P>

 <pre>
 	CF	Carry Flag	Non-Carry - indicates no error
 	EAX	Signature	'SMAP' - Signature to verify correct BIOS
 				revision.
 	ES:DI	Buffer Pointer	Returned Address Range Descriptor pointer.
 				Same value as on input.
 	ECX	Buffer Size	Number of bytes returned by the BIOS in the
 				address range descriptor.  The minimum size
 				structure returned by the BIOS is 20 bytes.
 	EBX	Continuation	Contains the continuation value to get the
 				next address descriptor.  The actual
 				significance of the continuation value is up
 				to the discretion of the BIOS.  The caller
 				must pass the continuation value unchanged
 				as input to the next iteration of the E820
 				call in order to get the next Address Range
 				Descriptor.  A return value of zero means that
 				this is the last descriptor.  Note that the
 				BIOS indicate that the last valid descriptor
 				has been returned by either returning a zero
 				as the continuation value, or by returning
 				carry.
 </pre>

 <HR>

 <H3>Address Range Descriptor Structure</H3>

 <pre>
 Offset in Bytes		Name		Description
 	0	    BaseAddrLow		Low 32 Bits of Base Address
 	4	    BaseAddrHigh	High 32 Bits of Base Address
 	8	    LengthLow		Low 32 Bits of Length in Bytes
 	12	    LengthHigh		High 32 Bits of Length in Bytes
 	16	    Type		Address type of  this range.
 </pre>

 The <I>BaseAddrLow</I> and <I>BaseAddrHigh</I> together are the 64 bit
 <I>BaseAddress</I> of this range.  The <I>BaseAddress</I>
 is the physical address of the
 start of the range being specified.<P>

 The <I>LengthLow</I> and <I>LengthHigh</I> together are the 64 bit
 <I>Length</I> of this range.
 The <I>Length</I> is the physical contiguous length in bytes of a range being
 specified.<P>

 The <I>Type</I> field describes the usage of the described address range as
 defined in the table below.<P>

 <pre>
 Value	Pneumonic		Description
 1	AddressRangeMemory	This run is available RAM usable by the
 				operating system.
 2	AddressRangeReserved	This run of addresses is in use or reserved
 				by the system, and must not be used by the
 				operating system.
 Other	Undefined		Undefined - Reserved for future use.  Any
 				range of this type must be treated by the
 				OS as if the type returned was
 				AddressRangeReserved.
 </pre>

 The BIOS can use the AddressRangeReserved address range type to block out
 various addresses as "not suitable" for use by a programmable device.<P>

 Some of the reasons a BIOS would do this are:<P>

 <UL>
 <LI>The address range contains system ROM.
 <LI>The address range contains RAM in use by the ROM.
 <LI>The address range is in use by a memory mapped system device.
 <LI>The address range is for whatever reason are unsuitable for a
 standard device to use as a device memory space.
 </UL>

 <HR>

 <H3>Assumptions and Limitations</H3>

 <UL>
 <LI><B>1.</B> The BIOS will return address ranges describing base board
 memory and ISA or PCI memory that is contiguous with that baseboard memory.
 <LI><B>2.</B> The BIOS WILL NOT return a range description for the memory
 mapping of PCI devices, ISA Option ROM's, and ISA plug & play cards.  This
 is because the OS has mechanisms available to detect them.
 <LI><B>3.</B> The BIOS will return chipset defined address holes that are not
 being used by devices as reserved.
 <LI><B>4.</B> Address ranges defined for base board memory mapped I/O devices
 (for example APICs) will be returned as  reserved.
 <LI><B>5.</B> All occurrences of the system BIOS will be mapped as reserved.
 This includes the area below 1 MB, at 16 MB (if present) and at
 end of the address space (4 gig).
 <LI><B>6.</B> Standard PC address ranges will not be reported.  Example video
 memory at A0000 to BFFFF physical will not be described by this
 function.  The range from E0000 to EFFFF is base board specific
 and will be reported as suits the bas board.
 <LI><B>7.</B> All of lower memory is reported as normal memory.  It is OS's
 responsibility to handle standard RAM locations reserved for
 specific uses,  for example: the interrupt vector table(0:0) and
 the BIOS data area(40:0).
 </UL>

 <HR>

 <H3>Example address map</H3>

 This sample address map describes a machine which has 128 MB RAM, 640K
 of base memory and 127 MB extended.  The base memory has 639K
 available for the user and 1K for an extended BIOS data area.  There
 is a 4 MB Linear Frame Buffer (LFB) based at 12 MB.  The memory hole
 created by the chipset is from 8 M to 16 M.  There are memory mapped
 APIC devices in the system.  The IO Unit is at FEC00000 and the Local
 Unit is at FEE00000.  The system BIOS is remapped to 4G - 64K.<P>

 Note that the 639K endpoint of the first memory range is also the base
 memory size reported in the BIOS data segment at 40:13.<P>

 Key to types: "ARM" is AddressRangeMemory, "ARR" is AddressRangeReserved.<P>

 <pre>
 Base (Hex)	Length	Type	Description
 0000 0000	639K	ARM	Available Base memory - typically the same
 				value as is returned via the INT 12 function.
 0009 FC00	1K	ARR	Memory reserved for use by the BIOS(s).
 				This area typically includes the Extended
 				BIOS data area.
 000F 0000	64K	ARR	System BIOS
 0010 0000	7M	ARM	Extended memory, this is not limited to
 				the 64 MB address range.
 0080 0000	8M	ARR	Chipset memory hole required to support the
 				LFB mapping at 12 MB.
 0100 0000	120M	ARM	Base board RAM relocated above a chipset
 				memory hole.
 FEC0 0000	4K	ARR	IO APIC memory mapped I/O at FEC00000.  Note
 				the range of addresses required for an APIC
 				device may vary from base OEM to OEM.
 FEE0 0000	4K	ARR	Local APIC memory mapped I/O at FEE00000.
 FFFF 0000	64K	ARR	Remapped System BIOS at end of address space.
 </pre>

 <HR>

 <H3>Sample operating system usage</H3>

 The following code segment is intended to describe the algorithm needed when
 calling the Query System Address Map function.  It is an implementation
 example and uses non standard mechanisms.<P>

 <pre>
     E820Present = FALSE;
     Regs.ebx = 0;
     do {
         Regs.eax = 0xE820;
         Regs.es  = SEGMENT (&Descriptor);
         Regs.di  = OFFSET  (&Descriptor);
         Regs.ecx = sizeof  (Descriptor);
 	Regs.edx = 'SMAP';

         _int( 0x15, Regs );

         if ((Regs.eflags & EFLAG_CARRY)  ||  Regs.eax != 'SMAP') {
             break;
         }

         if (Regs.ecx < 20  ||  Regs.ecx > sizeof (Descriptor) ) {
             // bug in bios - all returned descriptors must be
             // at least 20 bytes long, and can not be larger then
             // the input buffer.

             break;
         }

 	E820Present = TRUE;
 	.
         .
         .
         Add address range Descriptor.BaseAddress through
         Descriptor.BaseAddress + Descriptor.Length
         as type Descriptor.Type
 	.
         .
         .

     } while (Regs.ebx != 0);

     if (!E820Present) {
 	.
         .
         .
 	call INT 15h, AX=E801h and/or INT 15h, AH=88h to obtain old style
 	memory information
 	.
         .
         .
     }
 </pre>

 <HR>

 <A NAME="int15e801"><H1>INT 15h, AX=E801h - Get Memory Size for
 Large Configurations</H1></A>

 <HR>

 Real mode only (as far as I know).<P>

 Originally defined for EISA servers, this interface is capable of
 reporting up to 4 GB of RAM.  While not nearly as flexible as E820h, it
 is present in many more systems.<P>

 Input:<P>

 <pre>
 	AX	Function Code	E801h
 </pre>

 Output:<P>

 <pre>
 	CF	Carry Flag	Non-Carry - indicates no error
 	AX	Extended 1	Number of contiguous KB between 1 and 16 MB,
 				maximum 0x3C00 = 15 MB.
 	BX	Extended 2	Number of contiguous 64 KB blocks between
 				16 MB and 4 GB.
 	CX	Configured 1	Number of contiguous KB between 1 and 16 MB,
 				maximum 0x3C00 = 15 MB.
 	DX	Configured 2	Number of contiguous 64 KB blocks between
 				16 MB and 4 GB.
 </pre>

 Not sure what this difference between the "Extended" and "Configured"
 numbers are, but they appear to be identical, as reported from the BIOS.<P>

 NOTE:  It is possible for a machine using this interface to report a memory
 hole just under 16 MB (Count 1 is less than 15 MB, but Count 2 is
 non-zero).<P>

 <HR>

 <A NAME="int1588"><H1>INT 15h, AH=88h - Get Extended Memory Size</H1></A>

 <HR>

 Real mode only.<P>

 This interface is quite primitive.  It returns a single value for
 contiguous memory above 1 MB.  The biggest
 limitation is that the value returned is a 16-bit value, in KB,
 so it has a maximum saturation of just under 64 MB even presuming
 it returns as much as it can.  On some systems, it won't return
 anything above the 16 MB boundary.<P>

 The one useful point is that it works on every PC available.<P>

 Input:<P>

 <pre>
 	AH	Function Code	88h
 </pre>

 Output:<P>

 <pre>
 	CF	Carry Flag	Non-Carry - indicates no error
 	AX	Memory Count	Number of contiguous KB above 1 MB.
 </pre>

 <HR>

 <A HREF=mailto:erich@uruk.org><I>erich@uruk.org</I></A><P>

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	<HEAD>
	<TITLE>INT 15h, AX=E820h - Query System Address Map</TITLE>
	</HEAD>

	<BODY>

	<H1>INT 15h, AX=E820h - Query System Address Map</H1>
	<HR>

	Real mode only.<P>

	This call returns a memory map of all the installed RAM, and of physical
	memory ranges reserved by the BIOS. The address map is returned by making
	successive calls to this API, each returning one "run" of physical address
	information. Each run has a type which dictates how this run of physical
	address range should be treated by the operating system.<P>

	If the information returned from INT 15h, AX=E820h in some way differs from
	<A HREF="#int15e801">INT 15h, AX=E801h</A> or
	<A HREF="#int1588">INT 15h AH=88h</A>,
	then the information returned from E820h
	supersedes what is returned from these older interfaces.
	This allows the BIOS
	to return whatever information it wishes to for compatibility reasons.<P>

	<HR>

	Input:<P>

	<pre>
	EAX Function Code E820h
	EBX Continuation Contains the "continuation value" to get the
	next run of physical memory. This is the
	value returned by a previous call to this
	routine. If this is the first call, EBX
	must contain zero.
	ES:DI Buffer Pointer Pointer to an Address Range Descriptor
	structure which the BIOS is to fill in.
	ECX Buffer Size The length in bytes of the structure passed
	to the BIOS. The BIOS will fill in at most
	ECX bytes of the structure or however much
	of the structure the BIOS implements. The
	minimum size which must be supported by both
	the BIOS and the caller is 20 bytes. Future
	implementations may extend this structure.
	EDX Signature 'SMAP' - Used by the BIOS to verify the
	caller is requesting the system map
	information to be returned in ES:DI.
	</pre>

	Output:<P>

	<pre>
	CF Carry Flag Non-Carry - indicates no error
	EAX Signature 'SMAP' - Signature to verify correct BIOS
	revision.
	ES:DI Buffer Pointer Returned Address Range Descriptor pointer.
	Same value as on input.
	ECX Buffer Size Number of bytes returned by the BIOS in the
	address range descriptor. The minimum size
	structure returned by the BIOS is 20 bytes.
	EBX Continuation Contains the continuation value to get the
	next address descriptor. The actual
	significance of the continuation value is up
	to the discretion of the BIOS. The caller
	must pass the continuation value unchanged
	as input to the next iteration of the E820
	call in order to get the next Address Range
	Descriptor. A return value of zero means that
	this is the last descriptor. Note that the
	BIOS indicate that the last valid descriptor
	has been returned by either returning a zero
	as the continuation value, or by returning
	carry.
	</pre>

	<HR>

	<H3>Address Range Descriptor Structure</H3>

	<pre>
	Offset in Bytes Name Description
	0 BaseAddrLow Low 32 Bits of Base Address
	4 BaseAddrHigh High 32 Bits of Base Address
	8 LengthLow Low 32 Bits of Length in Bytes
	12 LengthHigh High 32 Bits of Length in Bytes
	16 Type Address type of this range.
	</pre>

	The <I>BaseAddrLow</I> and <I>BaseAddrHigh</I> together are the 64 bit
	<I>BaseAddress</I> of this range. The <I>BaseAddress</I>
	is the physical address of the
	start of the range being specified.<P>

	The <I>LengthLow</I> and <I>LengthHigh</I> together are the 64 bit
	<I>Length</I> of this range.
	The <I>Length</I> is the physical contiguous length in bytes of a range being
	specified.<P>

	The <I>Type</I> field describes the usage of the described address range as
	defined in the table below.<P>

	<pre>
	Value Pneumonic Description
	1 AddressRangeMemory This run is available RAM usable by the
	operating system.
	2 AddressRangeReserved This run of addresses is in use or reserved
	by the system, and must not be used by the
	operating system.
	Other Undefined Undefined - Reserved for future use. Any
	range of this type must be treated by the
	OS as if the type returned was
	AddressRangeReserved.
	</pre>

	The BIOS can use the AddressRangeReserved address range type to block out
	various addresses as "not suitable" for use by a programmable device.<P>

	Some of the reasons a BIOS would do this are:<P>

	<UL>
	<LI>The address range contains system ROM.
	<LI>The address range contains RAM in use by the ROM.
	<LI>The address range is in use by a memory mapped system device.
	<LI>The address range is for whatever reason are unsuitable for a
	standard device to use as a device memory space.
	</UL>

	<HR>

	<H3>Assumptions and Limitations</H3>

	<UL>
	<LI><B>1.</B> The BIOS will return address ranges describing base board
	memory and ISA or PCI memory that is contiguous with that baseboard memory.
	<LI><B>2.</B> The BIOS WILL NOT return a range description for the memory
	mapping of PCI devices, ISA Option ROM's, and ISA plug & play cards. This
	is because the OS has mechanisms available to detect them.
	<LI><B>3.</B> The BIOS will return chipset defined address holes that are not
	being used by devices as reserved.
	<LI><B>4.</B> Address ranges defined for base board memory mapped I/O devices
	(for example APICs) will be returned as reserved.
	<LI><B>5.</B> All occurrences of the system BIOS will be mapped as reserved.
	This includes the area below 1 MB, at 16 MB (if present) and at
	end of the address space (4 gig).
	<LI><B>6.</B> Standard PC address ranges will not be reported. Example video
	memory at A0000 to BFFFF physical will not be described by this
	function. The range from E0000 to EFFFF is base board specific
	and will be reported as suits the bas board.
	<LI><B>7.</B> All of lower memory is reported as normal memory. It is OS's
	responsibility to handle standard RAM locations reserved for
	specific uses, for example: the interrupt vector table(0:0) and
	the BIOS data area(40:0).
	</UL>

	<HR>

	<H3>Example address map</H3>

	This sample address map describes a machine which has 128 MB RAM, 640K
	of base memory and 127 MB extended. The base memory has 639K
	available for the user and 1K for an extended BIOS data area. There
	is a 4 MB Linear Frame Buffer (LFB) based at 12 MB. The memory hole
	created by the chipset is from 8 M to 16 M. There are memory mapped
	APIC devices in the system. The IO Unit is at FEC00000 and the Local
	Unit is at FEE00000. The system BIOS is remapped to 4G - 64K.<P>

	Note that the 639K endpoint of the first memory range is also the base
	memory size reported in the BIOS data segment at 40:13.<P>

	Key to types: "ARM" is AddressRangeMemory, "ARR" is AddressRangeReserved.<P>

	<pre>
	Base (Hex) Length Type Description
	0000 0000 639K ARM Available Base memory - typically the same
	value as is returned via the INT 12 function.
	0009 FC00 1K ARR Memory reserved for use by the BIOS(s).
	This area typically includes the Extended
	BIOS data area.
	000F 0000 64K ARR System BIOS
	0010 0000 7M ARM Extended memory, this is not limited to
	the 64 MB address range.
	0080 0000 8M ARR Chipset memory hole required to support the
	LFB mapping at 12 MB.
	0100 0000 120M ARM Base board RAM relocated above a chipset
	memory hole.
	FEC0 0000 4K ARR IO APIC memory mapped I/O at FEC00000. Note
	the range of addresses required for an APIC
	device may vary from base OEM to OEM.
	FEE0 0000 4K ARR Local APIC memory mapped I/O at FEE00000.
	FFFF 0000 64K ARR Remapped System BIOS at end of address space.
	</pre>

	<HR>

	<H3>Sample operating system usage</H3>

	The following code segment is intended to describe the algorithm needed when
	calling the Query System Address Map function. It is an implementation
	example and uses non standard mechanisms.<P>

	<pre>
	E820Present = FALSE;
	Regs.ebx = 0;
	do {
	Regs.eax = 0xE820;
	Regs.es = SEGMENT (&Descriptor);
	Regs.di = OFFSET (&Descriptor);
	Regs.ecx = sizeof (Descriptor);
	Regs.edx = 'SMAP';

	_int( 0x15, Regs );

	if ((Regs.eflags & EFLAG_CARRY) \|\| Regs.eax != 'SMAP') {
	break;
	}

	if (Regs.ecx < 20 \|\| Regs.ecx > sizeof (Descriptor) ) {
	// bug in bios - all returned descriptors must be
	// at least 20 bytes long, and can not be larger then
	// the input buffer.

	break;
	}

	E820Present = TRUE;
	.
	.
	.
	Add address range Descriptor.BaseAddress through
	Descriptor.BaseAddress + Descriptor.Length
	as type Descriptor.Type
	.
	.
	.

	} while (Regs.ebx != 0);

	if (!E820Present) {
	.
	.
	.
	call INT 15h, AX=E801h and/or INT 15h, AH=88h to obtain old style
	memory information
	.
	.
	.
	}
	</pre>

	<HR>

	<A NAME="int15e801"><H1>INT 15h, AX=E801h - Get Memory Size for
	Large Configurations</H1></A>

	<HR>

	Real mode only (as far as I know).<P>

	Originally defined for EISA servers, this interface is capable of
	reporting up to 4 GB of RAM. While not nearly as flexible as E820h, it
	is present in many more systems.<P>

	Input:<P>

	<pre>
	AX Function Code E801h
	</pre>

	Output:<P>

	<pre>
	CF Carry Flag Non-Carry - indicates no error
	AX Extended 1 Number of contiguous KB between 1 and 16 MB,
	maximum 0x3C00 = 15 MB.
	BX Extended 2 Number of contiguous 64 KB blocks between
	16 MB and 4 GB.
	CX Configured 1 Number of contiguous KB between 1 and 16 MB,
	maximum 0x3C00 = 15 MB.
	DX Configured 2 Number of contiguous 64 KB blocks between
	16 MB and 4 GB.
	</pre>

	Not sure what this difference between the "Extended" and "Configured"
	numbers are, but they appear to be identical, as reported from the BIOS.<P>

	NOTE: It is possible for a machine using this interface to report a memory
	hole just under 16 MB (Count 1 is less than 15 MB, but Count 2 is
	non-zero).<P>

	<HR>

	<A NAME="int1588"><H1>INT 15h, AH=88h - Get Extended Memory Size</H1></A>

	<HR>

	Real mode only.<P>

	This interface is quite primitive. It returns a single value for
	contiguous memory above 1 MB. The biggest
	limitation is that the value returned is a 16-bit value, in KB,
	so it has a maximum saturation of just under 64 MB even presuming
	it returns as much as it can. On some systems, it won't return
	anything above the 16 MB boundary.<P>

	The one useful point is that it works on every PC available.<P>

	Input:<P>

	<pre>
	AH Function Code 88h
	</pre>

	Output:<P>

	<pre>
	CF Carry Flag Non-Carry - indicates no error
	AX Memory Count Number of contiguous KB above 1 MB.
	</pre>

	<HR>

	<A HREF=mailto:erich@uruk.org><I>erich@uruk.org</I></A><P>

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