计算机系统结构11

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Fetch: An instruction and the necessary data are obtained from memory. Decode: The instruction and data are separated, and the components and pathways required to execute the instruction are activated. Execute: The instruction is performed, the data is manipulated, and the results are stored.
Buses
CSE2CSA Lecture 11
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Units & Buses

A unit in Computer Architecture is a piece of electronics which is a functional component in the architecture of a computer. A bus in Computer Architecture is a set of wires (parallel rails on a PC board) to send information from one unit to another unit in the computer. The buses of a computer connect the units together for transfer of information (data and control). Units are often implemented as single chips. The buses of different sorts connect the different pins on one chip to the pins on the other chips. The CPU also contains various units and its own internal processor buses connecting them. The flow of data inside a computer CPU from unit to unit via buses is referred to as a Datapath.

This pattern is typically implemented by separating the task into two components, the control, and the datapath.
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Control &aol: – The control unit reads the instruction, and activates the appropriate parts of the datapath. Datapath: – The datapath is the pathway that the data takes through the microprocessor. – As the data travels to different parts of the datapath, the command signals from the control unit cause the data to be manipulated in specific ways, according to the instruction. – The datapath consists of the circuitry for transforming data and for storing temporary data. It contains ALUs capable of transforming data through operations such as addition, subtraction, logical AND, OR, inverting, and shifting.
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The System Bus

The general architecture of a computer consists of a CPU, MM and peripherals connected by the System Bus consisting of a Control Bus, an Address Bus and a Data Bus:
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Memory Interconnection Organization
Datapath: Describes the collection of functional units within the Processor (CPU) that perform data processing operations. These functional units can be arithmetic logic units, multipliers and a range of registers. They are all connected by an internal bus which is a subsystem (originally parallel electrical wires) that transfers data between components:The adjacent diagram gives an overview of single (internal to the CPU) bus that provides the interconnection between these functional units. Some of the named functional units of the datapath include:• • • • • •
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Memory Interconnection Organization
Operationally, we can now view the input-process-output model within a computer in terms of the following:The processor (CPU) gets instructions and data from memory, input writes data to memory and output reads data from memory. Control sends signals that determine the operations of the datapath, memory, input and output. The following diagram represents the standard organization of a computer (this organization is independent of hardware technology every piece of every computer (past and present) fits into one of these five categories.
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Von Neumann Architecture


Early computer programs were hard wired. To reprogram a computer meant changing the hardware switches manually, that took a long time with potential errors. Computer memory was only used for storing data. John von Neumann suggested that data and programs should be stored together in memory. This is now called Von Neumann architecture. Programs are fetched from memory for execution by a central unit that we call the CPU. Basically programs and data are represented in memory in the same way. The program is just data encoded with special meaning. The main criticism of this approach is, that security problems can arise when instructions can be manipulated as if they were data, and vice-versa. A Von Neumann microprocessor is a processor that follows this pattern:
Attached peripheral devices.
Control Datapath Processor (CPU)
Interface Unit
Input Output Memory
As a minimum usually consists of:Monitor: Keyboard:
Disk: Other popular devices:Mouse, CD_ROM, LAN card, Speakers, Printer, Wireless connection,… .
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Memory Interconnection Organization
Input Output (I/O) interconnections Storage Effectively MEMORY