1. Field of the Invention
The present invention relates to a method and apparatus for controlling bus in a computer system to which an expansion unit is connectable.
2. Description of the Related Art
Conventionally, since an expansion unit for connecting an option device to a personal computer is built in a body of the personal computer, a type of a bus architecture is one and almost all architecture correspond to a standard.
However, in such a personal computer, there are the following problems.
More specifically, since the expansion unit is built in the body of the personal computer, only one type of the bus architecture can be equipped. Due to this, even if a plurality of bus architectures, for example, a 16 bus architecture and a 32 bit bus architecture exist, the option device for a bus architecture different from the bus architecture being used cannot be utilized. In a case where a 16 bit bus architecture is equipped in the personal computer, a 32 bit but architecture cannot be equipped therein. Due to this, a 32 bit option device cannot be connected to the personal computer.
Also, in a case where the bus architecture is built in the body of the computer, the performance of the computer is limited. In other words, even if the performances of a CPU, a peripheral device and the like are excellent, there is a case that these performances cannot sufficiently reflect the entire system since these performances depend on the built-in bus architecture.
For the above reason, in a case where the expansion unit is not connected in a personal computer to which the expansion unit is connectable, it is desirable that a bus control can be performed by a built-in bus controller in the personal computer. Or, in a case where the expansion unit is connected, it is desirable that the bus control can be performed by a bus controller of the expansion unit in place of the built-in bus controller.