What is the function of the address lines in the system bus?

The function of the address line is to select the main memory unit and I/O port. The full name of the address line is the address bus. It is a CPU or a unit with DMA capabilities. It is used to communicate that these units want to access (read/write) the physical address of the computer memory component/place; simply speaking, the address line is specifically used to transmit addresses. , determines where the information is sent.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

The system bus (English: System Bus) is a separate computer bus and is the main component connecting the computer system. This technology was developed to reduce costs and promote modularity. The system bus combines the functions of the data bus to carry information, the address bus determines where to send the information, and the control bus determines how to act.

The address line can be used to select both the main memory unit and the I/O port; the disk is connected to the host through the disk controller, so the address line in the system bus can only be used to select a port in a disk controller, not a disk block.

Address Bus (also known as: Address Bus) is a type of computer bus (part), which is used by CPU or units with DMA capabilities to communicate that these units want to access ( Read/write) the physical address of a computer memory element/place.

The width of the data bus varies with the size of the addressable memory component and determines how much memory can be accessed.

For example: a 16-bit width address bus (commonly used in 8-bit processors in the 1970s and early 1980s) reaches 2 to the 16th power = 65536 = 64 KB of memory address, and a 32-bit unit address bus (usually in a PC processor like today's 2004) can address 4,294,967,296 = 4 GB of addresses. But now many computer memories are larger than 4G (windows XP x32-bit system can only recognize a maximum of 3.29G, so if you want to use more than 4G of memory, you must use windows x64-bit system). Therefore, mainstream computers all have 64-bit processors, which means they can address 2^64=16X10^18=16EB addresses. This number will not be used up for a long time.

In most microcomputers (microcomputers), addressable components are 8-bit "bytes" (so "K" in this case is equivalent to "KB" or kilobyte), There are many examples of computers that use larger data blocks as their smallest physically addressable components, such as mainframes, supercomputers, and some workstation CPUs.

The address bus AB is specially used to transmit addresses. Since the address can only be transmitted from the CPU to the external memory or I/O port, the address bus is always one-way three-state, which is different from the data bus. The number of bits in the address bus determines the size of the memory space that the CPU can directly address. For example, if the address bus of an 8-bit microcomputer is 16 bits, its maximum addressable space is 2^16=64KB, and the address bus of a 16-bit microcomputer is 2^16=64KB. 20 bits, its addressable space is 2^20=1MB. Generally speaking, if the address bus is n bits, the addressable space is 2^n bits.

Technical indicators

1. Bus bandwidth (bus data transmission rate)

The bus bandwidth refers to the data transmitted on the bus per unit time Data volume, that is, the maximum steady-state data transfer rate of MB per clock. Two factors closely related to the bus are the bit width of the bus and the operating frequency of the bus.

2. The bit width of the bus

The bit width of the bus refers to the number of binary data bits that the bus can transmit simultaneously, or the number of bits of the data bus, that is, 32 bits, 64 bits, etc. The concept of bus width. The wider the bit width of the bus, the greater the data transfer rate per second, and the wider the bandwidth of the bus.

3. Bus operating frequency

The bus operating clock frequency is in MHZ. The higher the operating frequency, the faster the bus operating speed and the wider the bus bandwidth.

Calculation method of bus bandwidth: bus bandwidth = bus operating frequency * bus bit width / 8.

For example: For a 64-bit, 800MHz front-side bus, its data transfer rate is equal to 6.4GB/s=64bit×800MHz÷8(Byte); the data transfer rate of a 32-bit, 33MHz PCI bus is 132MB /s=32bit×33MHz÷8(Byte), etc.

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