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Quiz based on Digital Principles and Computer Organization

1) Base of hexadecimal number system? Answer : 16 2) Universal gate in digital logic? Answer : NAND 3) Memory type that is non-volatile? Answer : ROM 4) Basic building block of digital circuits? Answer : Gate 5) Device used for data storage in sequential circuits? Answer : Flip-flop 6) Architecture with shared memory for instructions and data? Answer : von Neumann 7) The smallest unit of data in computing? Answer : Bit 8) Unit that performs arithmetic operations in a CPU? Answer : ALU 9) Memory faster than main memory but smaller in size? Answer : Cache 10) System cycle that includes fetch, decode, and execute? Answer : Instruction 11) Type of circuit where output depends on present input only? Answer : Combinational 12) The binary equivalent of decimal 10? Answer : 1010 13) Memory used for high-speed temporary storage in a CPU? Answer : Register 14) Method of representing negative numbers in binary? Answer : Two's complement 15) Gate that inverts its input signal? Answer : NOT 16)...

Direct Memory Access

Direct Memory Access
* For devices that moves large quantities of data ( such as disk controllers ), it is wasteful to tie up the CPU transferring data in and out of registers one byte at a time.
* Instead this work can be off-loaded to a special processor, called as the Direct Memory Access, DMA, Controller.
* The host issues a command to the DMA controller, implicating the location where the data is located, the location where the data is to be moved to, and the number of bytes of data to moved. The DMA controller handles the data moved, and then interrupts the CPU when the transfer is complete.
* A simple DMA controller is a quality component in modern PCs, and many bus-
mastering I/O cards contain their possess DMA hardware.
* Handshaking between DMA controllers and their devices is fulfil by two wires called the DMA-request and DMA-acknowledge wires.
* While the DMA moves is going on the CPU does not have process to the PCI bus (including main memory ), but it does have process to its internal registers and primary and secondary caches.
* DMA can be complete in terms of either physical addresses or virtual addresses that are mapped to physical addresses. The latter method is known as Direct Virtual Memory Access, DVMA, and permits direct data transfer from one memory-mapped device to another without having the main memory chips.
* Direct DMA access by user processes can speed up operations, but is normally forbidden by modern systems for protection and security reasons. ( I.e. DMA is a kernel-mode operation. )
* Figure below shows the DMA process.

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