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# Little Man Computer, Clustering models, Main Memory Update

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Describe what the following LMC program does.

Mailbox Contents
00 901
01 309
02 207
03 902
04 708
05 602
06 000
07 1
08 000
09 DAT

b) The contents in memory occasionally have to be moved to another area of memory. When that happens, the mailbox references must be adjusted so that the program continues to function properly. Rewrite the LMC code in a) so that it occupies mailboxes 05 through 14 only; mailboxes 01 through 04 will be used by another program, so they can't be used. Assume that instruction 605 remains in mailbox 00.

Mailbox Contents
00 605
01 used by other program
02 used by other program
03 used by other program
04 used by other program
05 ???
06 ???
07 ???
08 ???
09 ???
10 ???
11 ???
12 ???
13 ???
14 ???

If a cache block is altered, what methods are used to update main memory? Of the various methods, which is faster?

Explain the basic differences between the shared-nothing model and shared-disk model in clustering computers.

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https://brainmass.com/computer-science/coding-and-information-theory/little-man-computer-clustering-models-main-memory-update-601628

#### Solution Preview

1a) Given LMC program accepts a number from user and then counts down from (number - 1) to 0. For example if user inputs 5, program will output 4, 3, 2, 1, 0 and halt.

I am giving explanation of different instructions to help you understand it.

Mailbox Contents Explanation
00 901 Accept input from user and store it in the accumulator.
01 309 Store the value from the accumulator in mailbox 09.
02 207 Subtract the value stored in mailbox 07 from current value of the accumulator.
03 902 Output the value of the accumulator.
04 708 Jump to mailbox location 08 if content of accumulator is 0.
05 602 Unconditionally jump to mailbox location 02.
06 000
07 1
08 000 Halt the program.
09 DAT

1b) When above LMC code occupies mailboxes 05 through 14 only (as mailboxes 01 through 04 will be used by another program), it will be rewritten as shown below. It is already given that instruction 605 remains in mailbox 00.

Mailbox Contents Explanation
00 605 Unconditionally jump to location 05.
01 used by other program
02 used by other program
03 used by other program
04 used by other ...

#### Solution Summary

Solution provides detailed explanation of LMC code. In case of comparison between shared-nothing and shared-disk clustering models, solution gives salient features of both the models in separate paragraph (for each) form. Student should be able to use that information to create point-wise comparison table easily.

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