Platform physical memory determination

NTDEV
1

Hi all,

Is there any kernel API which allows determining platform physical
memory size available?

Thanks,
Igor Markov

2

Posted by Igor Slewsarev to this list some time ago:

***************************************************************
Hi!
ZwQuerySystemInformation proto:

NTSYSAPI
NTSTATUS
NTAPI
ZwQuerySystemInformation(
IN SYSTEM_INFORMATION_CLASS SystemInformationClass,
IN OUT PVOID SystemInformation,
IN ULONG SystemInformationLength,
OUT PULONG ReturnLength OPTIONAL
);

typedef enum _SYSTEM_INFORMATION_CLASS {
SystemBasicInformation = 0,
// there are a lot of values, see “Windows NT/2000 Native API Reference”
// by Gary Nebbet for details
}SYSTEM_INFORMATION_CLASS;

typedef struct _SYSTEM_BASIC_INFORMATION {
ULONG Unknown; // Unknown
ULONG MaximumIncrement; // Timer increment in 100 ns units
ULONG PhysicalPageSize; // Hope, you know
ULONG NumberOfPhysicalPages; // Total number of pages manged by ntoskrnl
ULONG LowestPhysicalPage; // Lowest physical page number (usually
2 on PC)
ULONG HighestPhysicalPage; // Highest physical page number (This is
exactly you need)
ULONG AllocationGranularity;
ULONG LowestUserAddress;
ULONG HighestUserAddress;
ULONG ActiveProcessors;
UCHAR NumberProcessors;
} SYSTEM_BASIC_INFORMATION, *PSYSTEM_BASIC_INFORMATION;

However NumberOfPhysicalPages field is the number of pages managed by NT OS
memory manager; so this value is lower than the ‘real’ number of MB.
Note, some amount of memory is reserved for BIOS/Option ROM shadowing, some
for ACPI tables and etc.
*****************************************************************************

Dmitriy Budko, VMware

3

NtQuerySystemInformation is (partially) documented in the Platform SDK.

=====================
Mark Roddy
Windows .NET/XP/2000 Consulting
Hollis Technology Solutions 603-321-1032
www.hollistech.com

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Dmitriy Budko
Sent: Tuesday, January 11, 2005 5:31 PM
To: Windows System Software Devs Interest List
Subject: RE: [ntdev] Platform physical memory determination

Posted by Igor Slewsarev to this list some time ago:

***************************************************************
Hi!
ZwQuerySystemInformation proto:

NTSYSAPI
NTSTATUS
NTAPI
ZwQuerySystemInformation(
IN SYSTEM_INFORMATION_CLASS SystemInformationClass,
IN OUT PVOID SystemInformation,
IN ULONG SystemInformationLength,
OUT PULONG ReturnLength OPTIONAL
);

typedef enum _SYSTEM_INFORMATION_CLASS {
SystemBasicInformation = 0,
// there are a lot of values, see “Windows NT/2000 Native API
Reference”
// by Gary Nebbet for details
}SYSTEM_INFORMATION_CLASS;

typedef struct _SYSTEM_BASIC_INFORMATION {
ULONG Unknown; // Unknown
ULONG MaximumIncrement; // Timer increment in 100 ns units
ULONG PhysicalPageSize; // Hope, you know
ULONG NumberOfPhysicalPages; // Total number of pages
manged by ntoskrnl
ULONG LowestPhysicalPage; // Lowest physical page
number (usually
2 on PC)
ULONG HighestPhysicalPage; // Highest physical page
number (This is
exactly you need)
ULONG AllocationGranularity;
ULONG LowestUserAddress;
ULONG HighestUserAddress;
ULONG ActiveProcessors;
UCHAR NumberProcessors;
} SYSTEM_BASIC_INFORMATION, *PSYSTEM_BASIC_INFORMATION;

However NumberOfPhysicalPages field is the number of pages
managed by NT OS memory manager; so this value is lower than
the ‘real’ number of MB.
Note, some amount of memory is reserved for BIOS/Option ROM
shadowing, some for ACPI tables and etc.
**************************************************************
***************

Dmitriy Budko, VMware

Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

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