问cs-sub 91test的一些问题，请headlong帮忙
12.Which of the following statemengts describe properties of a purely segmented memory system?
1 O7 W; }; j3 ?! L/ FI.It divides memory into units of equal size.
5 |# u( D3 m# L3 |II.It permits implementation of virtual memory.
% \+ T' E* ]9 f8 \III.It suffers from internal fragmentation6 S' @/ O" M! A6 u2 H# S
(A) I only/ \& L6 k7 v0 H
(B)II only
& A O- N2 A2 d* D. U2 R(C)III only
) p7 d3 w3 o' d. R3 w& Z(D)I and III4 r) j; Q Y/ ]* A) X% q
(E)II and III% `# C0 j9 a. N2 H
答案是(B),可是III为什么不对呢，如果段的长度不是任意的，我觉得III也是有可能的 q/ `! K+ @$ D2 y& q7 c
################################################################################! b& \8 m& y- k4 M1 h/ q
14.procedure Insert(s:SetType;i:integer);
) [' b; X) V9 D/ l# o% z(* Precondition i不属于s0,where s0 denotes the value of s *)! @; x" ?' E: S* Y
(* Postcondition:s is the union of s0 and the single set {i} *)/ u5 ]2 r: l6 o$ G4 N- e" U
Which of the following statements is true concering the call Insert(s,i)?
8 X0 _' W7 M- o. B1 p. X% L7 fI if the precondition is met,then,upon return from the call to Insert,the size of s will have increased by 1.
5 Z! u4 f3 E0 @9 VII The writer of any code that includes a call to Insert can assume i is not in s prior to the call- y2 t* _7 S: Q: y
III The writer of any code for the body of Insert can assume i is not in s upon entrance to the procedure.% V- o) @% R' y% ?
(A) I noly (B)II only (C) III only (D) I and II (E) I and III0 v7 z% F" N$ f `0 ~" d
答案是(E),这道题的题意我不明白( G- T3 }' g/ z- _
###########################################################################* C; r8 E" ]3 q; I, r+ M
20 A sequential circuit emits a 1 if and only if a 1 has just been received and the system has received an even number of 0's and an even number of 1's since it was reset.The system resets on emiting a 1.Which of the following is a possible state diagram for this circuit,where A is the initial(start)state
7 z/ g; Z! k+ V) u/ v4 r" v(图我就不画了)0 n& [, _$ s5 P4 y& K- w9 o
答案是(E),我不懂它的题意，这种题应该怎么做呢？) A6 U0 X! e- c5 F7 s
#########################################################################
/ `6 V$ @' o0 C9 ?3 d21.Which of the following statemengts about circuits is true?4 }7 c% f0 U* U7 ?; \# p
I.Combinational circuits may have feedback;sequential circuits do not3 q9 c- o J! W: T' L: b
IICombinational circuits have a "memoryless" property;sequential circuits do not
5 U0 x2 g$ P5 O3 N1 Z3 m4 Q; T5 \III Both sequential and combinational circuits must be controlled by an external clock
% }5 x6 C! R, _7 y(A)I only
6 \% }+ f9 f. R# j- }(B)II only. P0 l$ {5 b3 Y5 B- ?; d/ O+ u: A+ N
(C)I and II only' ?$ Q! {3 O9 h5 G- Q/ h
(D)II and III only
6 ^/ w% e: @$ T. ^) { b(E)I,II,and III
2 E( O1 e o. T$ V; {答案是(B)
$ `, m9 Y/ k6 y$ a- O- \3 jI为什么不对阿？II中的"memoryless""property是什么意思？
6 Y& I% w2 M! K0 y做这种题需要复习数电么？可是我觉得数电好像也没有这些内容阿？
% Q, f1 `! L$ z9 j& d+ u#############################################################################/ |6 y& U% ^. _9 M6 m$ j s
24.Suppose sharing of files in a multilevel directory structure is achieved with directory entries that are links pointing to a node containing information about a shared file.Information in this node include (1)the owner of the file(2)a count of the number of links to the file,and (3)the disk block numbers of the file.What is a primary drawback to this approach to sharing?2 h2 r) Z3 u" l# H" v4 o. ?
(A) If the owner modifies the file,another user who does not share will see the changes
! g4 t% A/ y4 M" x4 ?) u. b(B)If the owner renames the file,other users will not be able to access it$ V- j, o/ E+ ^/ v" I
(C)If the owner is allowed to delete a file,dangling links may result# F: \' E# o: y, W
(D)If any user who shares the file appends to it,others who share it will not be able to access the new disk blocks./ s( P g5 @2 k6 D/ Z
(E)The system cannot know when blocks of a file can be reclaimed.
+ y2 F+ H5 T4 ~3 @7 O5 O$ c答案选(C),我不太明白，这道题怎么做，需要哪些知识？
3 k' }# K7 [) U5 H###########################################################################! ]% T. h# w3 G% `0 g C
25.Which of the following considerations applies(apply) to choosing the page size in a paging system?7 Q9 M, j. k4 ?. b& k# G
I An advantage of larger pages is that they lead to smaller page tables, n9 Y! ?* p( d; S0 d, d4 d
II An advantage of smaller pages is that they lead to less waste due to internal fragmentation! ^" _6 `( l2 r9 J8 i4 B+ T
III Normally,the dominant factor in disk access time is not dependent on page length,so longer pages can be used advantageously.
/ ], f, V/ i/ s \(A)I only (B)II only (C)I and III only (D) II and III only (E) I,II,and III
" a3 I, e' H8 ~. H5 M) R6 a# H7 M答案是(E),我不明白为什么III是对的
1 w$ n: t+ [! q' E/ A! ^# t
