Maximum Memory Capacity - NEC Express5800 User Manual

9-46 Upgrading Your Server

Maximum Memory Capacity

The available memory capacity depends on the basic architecture of the server (x86 architecture)
and specifications of supported operating systems.
Memory hole
– The x86 architecture (IA-32) adopts Memory Mapped I/O method which reserves the
fixed memory area (memory hole) for controlling various I/O devices (e.g., onboard
device and PCI devices).
– The memory hole reserves 4GB or less physical memory area as reserved memory area,
regardless of mounted memory capacity. The OS cannot access this reserved area, thus,
the available memory capacity may be less than the actual mounted memory capacity
due to the memory hole.
Memory Reclaim feature
– The server provides Memory Reclaim feature for complementation of memory hole.
– The Memory Reclaim feature remaps physical memory addresses in the memory hole
on hardware (chipset). By remapping, the whole capacity of mounted memory can be
used.
– Note, however, the remap memory area may not be available depending on the memory
capacity supported by OS. Accordingly, the available memory capacity depends on the
supported OS.
Memory hole
(with physical 4GB memory installed)
Physical
memory:
4GB
Physical Physical
memory:
memory
0GB
Memory capacity
Memory
unavailable for
hole
OS: (Approx.
700MB)
Memory capacity
available for OS:
Approx. 3.3GB
Memory Reclaim feature
(with physical 4GB memory installed)
Remap
memory
Physical
Memory
memory:
hole
4GB
Physical Physical
memory:
memory
0GB
Note: When the OS support memory can support the
total capacity of physical memory and memory
hole.
Memory capacity
unavailable for OS:
(Approx. 700MB)
Remaps physical
memory in the memory
hole on hardware.
The OS can use whole
physical memory
mounted.
Memory capacity
available for OS:
Approx. 3.3GB