Chapter 2 Organization of Computers 2.1.1 System Buses The system shown in Figure 2-l has three buses. The uppermost bus in this figure is the address bus. When the cPu reads data or instructions from or writes data to memory, it must specify the address of the memory location it wishes to access. It outputs this address to the address bus; memory inputs this address from the address bus and use it to access the proper memory location. Each l/o devices such as a keyboard, monitor, or disk drive, has a unique address as well.When accessing an I/O device, the CPu places the address of the device on the address bus. Each device can read the address off of the bus and determine whether it is the device being accessed by the cPu. Unlike the other buses the address bus al ways receives data from the CPU; the CPu never reads the address bus 图2-1所示的系统包括三组总线。最上面的是地址总线。当CPU从存储器读取数据或 指令,或写数据到存储器时,它必须指明将要访问的存储器单元地址。CPU将地址 输出到地址总线上,而存储器从地址总线上读取地址,并且用它来访问正确的存储 单元。每个IO设备,比如键盘、显示器或者磁盘,同样都有一个唯一的地址。当访 问某个O设备时,CPU将此设备的地址放到地址总线上。每一个设备均从总线上读 取地址并且判断自己是否就是CPU正要访问的设备。与其他总线不同,地址总线总 是从CPU上接收信息,而CPU从不读取地址总线 计算机专业英语 2-8Chapter 2 Organization of Computers 计算机专业英语 2-8 The system shown in Figure 2-1 has three buses. The uppermost bus in this figure is the address bus. When the CPU reads data or instructions from or writes data to memory, it must specify the address of the memory location it wishes to access. It outputs this address to the address bus; memory inputs this address from the address bus and use it to access the proper memory location. Each I/O devices, such as a keyboard, monitor, or disk drive, has a unique address as well. When accessing an I/O device, the CPU places the address of the device on the address bus. Each device can read the address off of the bus and determine whether it is the device being accessed by the CPU. Unlike the other buses, the address bus always receives data from the CPU; the CPU never reads the address bus. 图2-1所示的系统包括三组总线。最上面的是地址总线。当CPU从存储器读取数据或 指令，或写数据到存储器时，它必须指明将要访问的存储器单元地址。CPU将地址 输出到地址总线上，而存储器从地址总线上读取地址，并且用它来访问正确的存储 单元。每个I/O设备，比如键盘、显示器或者磁盘，同样都有一个唯一的地址。当访 问某个I/O设备时，CPU将此设备的地址放到地址总线上。每一个设备均从总线上读 取地址并且判断自己是否就是CPU正要访问的设备。与其他总线不同，地址总线总 是从CPU上接收信息，而CPU从不读取地址总线。 2.1.1 System Buses