Intel
®
Chipset 4 GB System
Memory Support
White Paper
February 2005
Revision 1.0
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INFORMATION IN THIS DOCUMENT IS PROVIDED IN CONNECTION WITH INTEL
®
PRODUCTS. NO LICENSE, EXPRESS OR IMPLIED, BY
ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. EXCEPT AS PROVIDED IN
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Contact your local Intel sales office or your distributor to obtain the latest specifications and before placing your product order.
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Copyright © 2004-2005, Intel Corporation. All rights reserved.
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Contents
1
Preface................................................................................................................................5
1.1 Key Takeaways ......................................................................................................5
2 Platform Memory Subsystem Usage ..................................................................................7
2.1 Definition of Address Ranges.................................................................................7
2.2 Memory Initialization and Assignment of Resources ............................................. 7
2.3 Microsoft Operating System Memory Support ....................................................... 9
3 Recommended System BIOS Updates and Documentation Changes ............................11
3.1 System BIOS Display of Available vs. Populated Memory ..................................11
3.2 Documenting Chipset Capabilities ....................................................................... 11
4 Memory Remapping..........................................................................................................13
4.1.1 Memory Re-mapping Algorithm............................................................13
4.1.2 Example: Greater than 4 GB of Physical Memory:............................... 14
4.1.3 Interaction with Other Overlapping Address Space .............................15
4.1.4 Implementation Notes...........................................................................15
4.1.5 Unmapped Addresses between TOLM and 4 GB................................15
5 Experimental Data............................................................................................................. 17
Figures
Figure 1: Example BIOS Information Screen.................................................................... 12
Tables
Table 1. E820h Table from Reference Intel
®
915G Express Chipset-Based Platform
with Internal Graphics ................................................................................................ 17
Table 2. Intel
®
915G Express Chipset-Based Platform with Microsoft Windows* XP
and Service Pack 2...................................................................................................18
Table 3. Intel
®
915G Express Chipset-Based Platform with Microsoft Windows* XP
64-Bit Edition..............................................................................................................18
Table 4. Intel
®
915G Express Chipset-Based Platform with RedHat* Enterprise Linux...19
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Revision History
Revision
Number
Description Revision Date
0.5
• Initial Release
September 2004
1.0
• Redesignated as public document
February 2005
Preface
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1 Preface
This document addresses potential customer questions that may arise when a system is populated
with the maximum memory configuration (e.g., 4 GB for an Intel
®
915G Express chipset), and the
operating system (OS) reports less available memory than that populated (OS reports
approximately 3.2 GB of available memory). It is intended for training of customer support and
field personnel at hardware system manufacturers and for software developers of applications,
operating system, and tools.
This document outlines the division and potential overlap of the addressable physical and virtual
memory ranges by system BIOS for required system and PC architectural resources and operating
system usage.
It offers background on ways that system developers may mitigate the potential overlaps and
better describe the memory usage to the end customer. The first method used to decrease potential
overlaps is memory remapping, used today by some workstation and server chipsets to maximize
the amount of populated system memory that can be allocated to operating systems. Possible
solutions that the system BIOS may incorporate to clearly delineate via setup menus include:
populated, system resource, and operating system available memory.
This document also provides experimental results using a current desktop platform as a base line
and a mid-range server platform that incorporates memory remapping to show the potential gains
with multiple operating systems and varying amounts of system memory. Experimental data is not
inclusive of all available or potentially available chipset solutions, memory sizes platform
configurations, or operating system variations.
1.1 Key Takeaways
• Due to PC architectural requirements such as motherboard resources and OS limitations,
desktop platforms using larger memory may be unable to take full advantage of all memory
populated on the system.
• When systems with chipsets that support 4 GB or less of system memory are populated with
the maximum system memory of 4 GB, the operating system (OS) may report a lower amount
of available memory
• Standard PC Architecture System Resources require addressing which overlaps physical
memory below 4 GB:
⎯ System BIOS
⎯ Motherboard Resources (I/OxAPIC)
⎯ Memory Mapped I/O
⎯ PCI Express* Configuration Space
⎯ Additional PCI Device Memory (Graphics Aperture)
⎯ VGA Memory
⎯ Others as included, etc.
• These requirements may reduce the addressable memory space available to and reported by
the operating system
