Computer buses

The basis of any personal computer is the motherboard and processor. They are dependent on the performance of the entire system. On the motherboard for each device - the keyboard, disk drives, etc., has a control electronic circuit - adapter or controller. Some controllers can manage multiple devices.

All computer controllers interact with the processor and memory system via the data highway, which is also called the system bus

All computer controllers interact with the processor and memory system via the data highway, which is also called the system bus. In addition to the system bus on modern motherboards, there are several buses and the corresponding connectors for devices:

  1. the memory bus - for the exchange of information between the RAM and the CPU;
  2. bus AGP - to connect video;
  3. the bus cache - for the exchange of information between the cache memory and the CPU;
  4. IO bus (bus interface) - are used to connect various devices.

There are three main indicators computer bus operation: clock frequency, bit rate, data rate or bandwidth.

Operation of any computer depends on the clock frequency determined by a crystal oscillator which is a tin container placed therein quartz crystal. electrical oscillations occur under the influence of an electric voltage in the crystal. The frequency of these oscillations is called clock frequency. All changes are logical signals to any computer chip occurs at regular intervals, called cycles. Thus, the smallest unit of time for most computer devices have logical clock cycle. Each operation requires a minimum of one clock cycle, although some modern devices have time to perform multiple operations in one clock cycle. PC clock frequency is measured in megahertz (MHz or GHz). There are so-called empty cycles (wait states) when the device is in the process of waiting for a response from any other device. It is the work of memory and computer processor clock frequency is much higher clock speed RAM.

To transmit electrical signals using a plurality of channels of the bus. If you are using 32 channels, the tires are considered 32-bit if 64 channels - the 64-bit bus. In fact, any bus width have a greater number of channels. Additional channels are used to transmit specific information.

Each computer bus differs from a simple conductor that has three types of lines: data lines (data bus), the address lines (address bus), the control lines (control bus).

By bus data is exchanged between the CPU installed in the card slot expansion, and the computer's memory.

The process of data exchange is possible only in the case where the sender and recipient know these data. Each component of a personal computer and each cell has its own memory address includes the common address space. To address to any device serves as the address bus, which is transmitted by a unique address. The maximum amount of memory depends on the computer's bit address bus (number of lines) and is equal to 2n, where n - number of bus lines address. For example, computers with 80486 processor or higher have a 32-bit address bus, which can be used to address 4GB.

To successfully transmit data on the bus is not enough to set them on the data bus, and specify the address on the address bus. We need some more service signals, which are transmitted by the computer control bus.

Performance of each computer bus is characterized by its bandwidth, the maximum possible amount of information transmitted on the bus at a time, and is measured in MB/s or GB/s. The capacity of the bus is determined by the product of bit data line and the clock frequency. The higher the bandwidth, the higher the performance of the entire system.

In fact, on a computer bus bandwidth affects many kinds of factors: inefficient conductivity in materials, design and workmanship defects and more. The difference between the theoretical data transfer speed and may be practical to 25%.