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Assignment Three: Whole Course OS SP15

Q1:- Break the following monoalphabetic cipher. The plaintext, consisting of letters only, is
a well-known excerpt from a poem by Lewis Carroll.
kfd ktbd fzm eubd kfd pzyiom mztx ku kzyg ur bzha kfthcm
ur rnfudm zhx mftnm zhx mdzythc pzq ur ezsszcdm zhx gthcm
zhx pfa kfd mdz tm sutythc fuk zhx pfdkfdi ntcm fzld pthcm
sok pztk z stk kfd uamkdim eitdx sdruid pd fzld uoi efzk
rui mubd ur om zid uok ur sidzkf zhx zyy ur om zid rzk
hu foiia mztx kfd ezindhkdi kfda kfzhgdx ftb boef rui kfzk

Q2:-Are critical regions on code sections really necessary in an SMP operating system toavoid race conditions or will mutexes on data structures do the job as well?

Q3:-What happens if two CPUs in a multiprocessor attempt to access exactly the same
word of memory at exactly the same instant?

Q4:- RAID level 3 is able to correct single-bit errors using only one parity drive. What isthe point of RAID level 2? After all, it also can only correct one error and takes moredrives to do so.

Q5:- A computer whose processes have 1024 pages in their address spaces keeps its page tables in memory. The overhead required for reading a word from the page table is 5 nsec. To reduce this overhead, the computer has a TLB, which holds 32 (virtual page,physical page frame) pairs, and can do a look up in 1 nsec. What hit rate is needed toreduce the mean overhead to 2 nsec?



  • Questions are taken from Modern Operating Systems book ed 3
  • Deadline Wed 10 June 1630 hours

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