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A system bus is a single computer bus that connects the major components of a computer system, combining the functions of a data bus to carry information, an address bus to determine where it should be sent or read from, and a control bus to determine its operation. The technique was developed to reduce costs and improve modularity, and ...
Four PCI Express bus card slots (from top to second from bottom: ×4, ×16, ×1 and ×16), compared to a 32-bit conventional PCI bus card slot (very bottom). In computer architecture, a bus (historically also called a data highway [1] or databus) is a communication system that transfers data between components inside a computer or between computers. [2]
Some other computer architectures use different modules with a different bus width. In a single-channel configuration, only one module at a time can transfer information to the CPU. In multi-channel configurations, multiple modules can transfer information to the CPU at the same time, in parallel.
In computer architecture, a control bus is part of the system bus and is used by CPUs for communicating with other devices within the computer. While the address bus carries the information about the device with which the CPU is communicating and the data bus carries the actual data being processed, the control bus carries commands from the CPU and returns status signals from the devices.
On the PDP-6/10, special instructions operated on a byte pointer which included a word address, a bit offset, and a bit width. The LDB / DPB instructions loaded or stored one byte, the IBP instruction incremented the byte pointer, and the ILDB / IDPB instructions incremented the byte pointer and then loaded or stored the next byte. These ...
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
[citation needed] From a software point of view, the mechanism works exactly as before, and an operating system must still program external hardware (which in-turn sends the aforementioned bus cycles to the CPU) to disable the A20 masking. [citation needed] Intel no longer supports the A20 gate, starting with Haswell. Page 271 of the Intel ...
The high-order byte of the instruction specifies the operation. Bits 9 through 15 are the op-code, and bit 8 is the value of the condition code calculation which results in the branch being taken. The low-order byte is a signed word offset relative to the current location of the program counter. This allows for forward and reverse branches in code.