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The simplest system bus has completely separate input data lines, output data lines, and address lines. To reduce cost, most microcomputers have a bidirectional data bus, re-using the same wires for input and output at different times. [20] Some processors use a dedicated wire for each bit of the address bus, data bus, and the control bus.
In computing, an input–output memory management unit (IOMMU) is a memory management unit (MMU) connecting a direct-memory-access–capable (DMA-capable) I/O bus to the main memory. Like a traditional MMU, which translates CPU -visible virtual addresses to physical addresses , the IOMMU maps device-visible virtual addresses (also called device ...
The 11/45 architecture expanded to allow 4 MB of physical memory segregated onto a private memory bus, 2 KB of cache memory, and much faster I/O devices connected via the Massbus. PDP–11/34 (1976 [ 15 ] ) and PDP–11/04 (1975 [ 15 ] ) – Cost-reduced follow-on products to the 11/35 and 11/05; the PDP–11/34 concept was created by Bob ...
Each device can request up to six areas of memory space or input/output (I/O) port space via its configuration space registers. In a typical system, the firmware (or operating system ) queries all PCI buses at startup time (via PCI Configuration Space ) to find out what devices are present and what system resources (memory space, I/O space ...
The name originates from the Basic Input/Output System used in the CP/M operating system in 1975. [2] [3] The BIOS firmware was originally proprietary to the IBM PC; it was reverse engineered by some companies (such as Phoenix Technologies) looking to create compatible systems. The interface of that original system serves as a de facto standard.
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.
The input/output instructions all start with bits 0 through 2 being set to 1 (decimal value 7), bits 3 through 9 containing a device number, and 10 through 12 the instruction opcode. [ 22 ] In both formats, bits 13 through 35 are used to form the "effective address", E. Bits 18 through 35 contain a numerical constant address, Y.
SBus is a computer bus system that was used in most SPARC-based computers (including all SPARCstations) from Sun Microsystems and others during the 1990s. It was introduced by Sun in 1989 to be a high-speed bus counterpart to their high-speed SPARC processors, replacing the earlier (and by this time, outdated) VMEbus used in their Motorola ...