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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)...

VIRTUAL MEMORY

Virtual Memory
* Virtual memory is a characteristics of an operating system that allows a computer to be adept to compensate shortages of physical memory by transferring pages of data from random access memory to disk storage
* In practice, most real processes do not require all their pages, or at least not all at once, for several reasons:
 • Error handling code is not required unless that specific error occurs, some of which are quite rare.
• Arrays are often over-sized for worst-case schemes, and only a small fraction of the arrays are actually used in practice.
• Definite features of definite programs are rarely used, such as the routine to balance 
the federal budget. 
*The potential to load only the portions of processes that were actually needed (and only when they were needed) has several benefits:
•Programs could be written for a much longer address space(virtual memory space) than physically exists on the computer.
• Because each process is only using a fraction of their overall address space, there is more memory left for other programs, increasing CPU utilization and system throughput.
• Small I/O is needed for swapping  in and out of RAM, speeding things up.
* Figure below shows the general layout of virtual memory, which can be much longer 
than physical memory:
Fig: Diagram showing virtual memory is larger than physical memory
* Figure below conveys virtual address space, which is the programmer’s logical view of process memory storage. The actual physical layout is managed by the process's page table.
* Note that the address space shown in Figure is sparse - A great hole in the middle of the address space is never used, unless the stack and/or the heap grow to fill the hole.
Fig: Virtual address space
* Virtual memory also permits the sharing of files and memory by multiple processes, with several benefits:
• System libraries can be divided by mapping them into the virtual address space of more than one process.
• Processes can also divides virtual memory by mapping the same block of memory to more than one process.
• Process pages can be divided during a fork( ) system call, eliminating the need to 
copy all of the pages of the actual(parent) process.



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