System address space, PCI address space

System address space, PCI address space
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1




System address space and
PCI



Address Space

1.1



PCI



Address Space

PCI

Bus has
32

Bit Data
/

Address reuse bus, so its storage address space is
Power 32 of 2 = 4 GB

. That is
PCI

All devices on are mapped to this
4 GB

, Each
PCI

The device occupies a unique segment.
PCI

Address to facilitate
PCI

Unified bus addressing. Each
PCI

Device pass
PCI

The base address register in the Register to specify the first address of the ing.
PCI

The address space corresponds
PCI

Bus.

 

One
PCI

Device possession
PCI

Part of the bucket,
PCI

The decoding of the memory address is distributed on the device. Each device is responsible for its own decoding and selects signals from the external input device after the central decoding is not required.

1.2




System address space

If the processor has
32

The theoretical addressable space of the bit address bus is
Power 32 of 2 = 4 GB

. But this does not mean that the memory can be
4 GB

Size, in fact
XP

The maximum system memory is approximately
2 GB

, Which corresponds
CPU

The method of accessing the memory of other devices in the system (for example
CPU

Access
PCI

Memory on the bus ).

There are different devices in different physical locations in the computer system, and different devices have their own memory.
CPU

How to access these memories?
CPU

Maps the storage space of each device in the system to a unified storage space.
4 GB


CPU

You can access all the memory. For example
PCI

Memory ing to from
0xfff80000

The starting address space is mapped to the video card
0xfff00000

In addition, the operating system will occupy some space, and there will be no space left.
2G

It can be actually allocated to the physical memory. (The specific value is an interpreted value, which does not represent the actual situation)

The system address space corresponds to the front-end bus (
FSB

).

Visible,
PCI
Address Space (
4 GB
) Cannot be fully mapped to the system address space (
4 GB
), And the system address space occupied by the ing cannot be too large. Otherwise, it will occupy the system address space of the physical memory, and some physical memory cannot be accessed.