PCI hole-swallowed memory

See wiki: http://en.wikipedia.org/wiki/PCI_hole

PCI Holes

PCI holes are a 32-bit hardware and 32-bit operating system, which causes the computer to display less memory than the actually installed memory. This part of memory is unavailable because the device needs address space to communicate with the CPU and system software. 32-bit hardware only has 4 GB addressable address space, so in order to make the device have space to communicate, A part of the real physical memory on a machine with enough memory has to be placed in the device address space (this varies with the machine, generally between 2.5 and GB ), this part of memory will be hidden to provide space for the installed devices.

The number of hidden system memory depends on the number of used motherboard and chipset, bios, physical memory, and video RAM on the video card, there is a big difference between the number and type of PCI cards installed on the system. After 4 GB physical memory and multiple 3D graphics cards with large memory are installed on a 32-bit system, more than 1 GB memory will be unavailable. On some motherboard, the holes will have at least 1 GB of memory, no matter what PCI Card is installed.

Physical address extension

PAE technology allows 32-bit operating systems to access 36-bit memory addresses, even if individual applications still have to use only 32-bit address space. Each program has its own 4 GB address space, and all applications add up to access 64 GB address space.

Fill in memory Holes

Memory is available on 64-bit systems at the top and bottom of the memory holes, but 500 to MB memory is not available because the device requests to use these address spaces. As the Memory price drops, this will not be a big problem, but there is still a way to re-access these lost memory.

Address mapped to a device larger than 4 GB

Omitted

Address mapped to memory above 4 GB

Omitted

 

PCI hole-swallowed memory