Computer Architecture 2072
Long Questions:
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Attempt any two questions. (2×10=20)
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1. Explain address mapping using pages. A virtual memory system has an address space of 8K words, a memory space of 4K words, and page and block sizes of 1K words The following page reference changes occur during a given time interval. (Only page changes are listed. If the same page is referenced again, it is not listed twice).
4 2 0 1 2 6 1 4 0 1 0 2 3 5 7
Determine the four pages that are resident in main memory after each page reference change if the replacement algorithm used is (a) FIFO (b) LRU
Address Mapping Using Pages
A physical memory is broken down into groups of equal
size called blocks or page frame and the groups of address space of the same
size as block is called pages.
Consider a computer a with address space =8K and memory space=4K
Virtual address has 13 bits. Since each page consists
of 210=1024 words, high-order 3 bits will specify one of 8 pages and
low-order 10 bits gives the line address within the pages.
In computer 2p words per page, p bits are used to specify a line address and remaining high-order bits of the virtual address specify the page number and an address for the memory page table. Line address in memory space and address space is same; only mapping required is from page number to a block number.
The memory page table consists of 8 words, one for
each page. The address in the page table denotes page number and the content of
word gives the block number where the page is stored in main memory.
Presence bit when 0 indicates page is not available in main memory and when 1 indicates that page has been transferred to main memory. Table shows that pages 1, 2, 5 & 6 are now available in main memory in blocks 3, 0, 1 & 2 respectively.
Second Part
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2. Why do computers need input-output interface? Explain the sequence of operations carried out during CPU-IOP communication with the help of suitable flowchart.
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3. What is a microprogram sequencer? With block diagram, explain the working of microprogram sequencer.
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Short Questions:
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Answer any ten questions: (10x6=60)
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4. Differentiate between address space and memory space. An address space is specified 2 bits and the corresponding memory space by 16 bits. If a page consists of 2K words, how many pages and blocks are there in the system?
Difference between address space and memory space
An address used by programmer is a virtual address and
the set of such addresses is the address space. Thus the address space is the
set of addresses generated by the programs as they reference instructions and
data. Generally, the address space is larger than the memory space.
An address in main memory is called a location or
physical address. The set of such locations is called the memory space. The
memory space consists of actual main memory locations directly addressable for
processing. Generally, the memory space is smaller than the address space.
Second Part:
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5. What do you mean by interrupt? Draw and explain the flowchart for interrupt cycle.
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6. Explain with an example, how effective address is calculated in different types of addressing modes.
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7. What the difference is between isolated and memory mapped I/O? What are the different types of I/O commands.
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8. Show the memory organization (1024 bytes) of a compute with four 128x8 RAM Chips and 512x8 ROM Chip. How many address lines are required to access memory?
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9. Show the step-by-step multiplication process using booth’s algorithm, when +14 is multiplied by -14. Assume 5-bit registers that hold signed numbers.
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10. Briefly explain fixed-point representation of numbers. What is the signed magnitude, 1’s complement and 2’s complement of -9?
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11. Explain about the basic computer instruction format. When instruction set is said to be complete.
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12. Explain Overlapped register windows with suitable example.
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13. Example the process of overflow detection with both signed and unsigned numbers.
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14. Define selective-set, selective-complement, selective-clear, mask, insert and clear operation with an example.
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15. Write short notes on the following.
a) Integer representation
b) Subroutines
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