设计高质量的软件是软件设计追求的一个重要目标。可移植性、可维护性、可靠性、效率、可理解性和可使用性等都是评价软件质量的重要方面。可移植性反映出把一个原先在某种硬件或软件环境下正常运行的软件移植到另—个硬件或软件环境下，使该软件也能正确地运行的难易程度。为了提高软件的可移植性，应注意提高软件的(47)。可维护性通常包括(48)。通常认为，软件维护工作包括改正性维护、(49)维护和(50)维护。其中(49)维护则是为了扩充软件的功能或提高原有软件的性能而进行的维护活动。(51)是指当系统万一遇到未预料的情况时，能够按照预定的方式做合适的处理。

(127)

(128)

(126)

(125)

The　"main　storage"　normally　means　that　part　of　internal　storage　into　which　instructions　and　other　data　must　be　loaded　for　subsequent　execution　or　processing.　In　large　computing　systems,　the　term　"main　storage"　is(71) to　"memory".　"Buffer"　mainly　indicates　a　special-purpose　storage　or　storage　area　allowing,　through(72) storage,　the　data　transfer　between　two　functional　units　having　different　transfer　characteristics.　A　buffer　storage　is　used　between　non-synchronized　devices　or　where　one　is(73) and　the　other　is　parallel　or　between　those　having　different　trans　far　rates.　"(74) (memory)"　is　also　a　special-purpose　buffer　storage,　smaller　and　faster　than　main　storage,　used　to　hold　a　copy　of　instructions　and　data　obtained　from　main　storage　and　likely　to　be　needed　next　by　the　processor.　"Register"　is　commonly　composed　of　a　part　of　internal　storage　having　a　specified　storage(75) and　usually　intended　for　a　specific　purpose.

(123)

(122)

(121)

(120)

(66) program　propagates　itself　by　modifying　other　programs　to　include　a　possibly　changed　copy　of　itself　and　that　is　executed　when　the　infected　program　is(67).　A　virus　often　causes　damage　or　annoyance　and　may　be　triggered　by　some　event　such　as　the　occurrence　of　a　predetermined　date.Worm　is　a　self-contained　program　that　can　propagate　itself　through　data　processing　systems　or　computer　networks.　Worms　are　often　designed　by　hackers　to　use　up(68) resources　such　as　storage　space　or　processing　time.Trojan　horse　implies　by　the　name　an　apparently　harmless　program　containing(69) logic　that　allows　the　unauthorized　collection,　falsification　or　destruction　of　data.　Logic　bomb　causes　damage　to　a　data　processing　system　when　triggered　by　some　specific　system　condition.　Time　bomb　is　also　a　malicious　program　being　activated　at　a(70) time.