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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)...

Stable storage implementation

Stable-Storage Implementation
* The concept of stable storage includes a storage medium in which data is never lost, even in the face of equipment failure in the middle of a write operation.
* To implement this requires two (or more) copies of the data, with separate failure modes.
* An attempted disk write results in one of three possible outputs:
• The data is successfully and completely written.
• The data is partially written, but not completely. The last block written may be 
garbled.
• No writing takes place at all.
* Whenever an equipment failure occurs during a write, the system must detect it, and return the system back to a consistent state. To do this requires two physical blocks for every logical block, and the following procedure:
• Write the data to the first physical block.
• After step 1 had completed, then write the data to the second physical block.
• Declare the operation complete only after both physical writes have completed 
successfully.
* During recovery the pair of blocks is examined.
• If both blocks are identical and there is no sign of damage, then no further action 
is necessary.
• If one block contains a detectable error but the other does not, then the damaged 
block is replaced with the good copy. (This will either undo the operation or 
complete the operation, depending on which block is damaged and which is 
undamaged.)
• If neither block shows damage but the data in the blocks differ, then replace the 
data in the first block with the data in the second block. (Undo the operation.)
* Because the sequence of operations described above is slow, stable storage usually includes NVRAM as a cache, and declares a write operation complete once it has been written to the NVRAM.

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