英语翻译
In most modern computers main memory is volatile which means that it looses its memory when the power is removed.
Memory is divided into many identical storage cells.
Each cell contains a fixed number of bits.
Eight bit cells are called bytes.
Each storage cell is given a unique address,which is called the cell's location
A CPU only has two ways to access a memory location,such as Read and Write.
The I/O Subsystem provides a consistent link to the many I/O devices attached to the computer system
A CPU accesses devices via I/O ports.
There are two computer design techniques used for accessing I/O ports:
Access the port as a memory address.CPUs that implement this technique reserve a special range of memory addresses for I/O ports.
Use a separate addressing mechanism.CPUs that reserve a separate address space for I/O ports must use special instructions for accessing the ports.
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