Suppose that a basic disk read can sometimes read values that are different from those written. State the type of failure exhibited by a basic disk read. Suggest how this failure may be masked in order to produce a different benign form of failure. Now suggest how to mask the benign failure.
What will be an ideal response?
The basic disk read exhibit arbitrary failures.
This can be masked by using a checksum on each disk block (making it unlikely that wrong values will go undetected) - when an incorrect value is detected, the read returns no value instead of a wrong value - an omission failure.
The omission failures can be masked by replicating each disk block on two independent disks. (Making omission failures unlikely).
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_________ methods can be called without the need for an object of the class to exist.
a) special b) independent c) static d) dependent
Categorize each of the following usability specifications as a performance measure or a preference measure. Justify your answers.
a. Users should be able to login in within 3 minutes, even if they forget their passwords. b. On a scale of 1 to 5 where 1 is “very difficult” and 5 is “very easy”, ninety percent of the users should rate the login process a 4 or above c. Users should hit the “back” button no more than 2 times when looking for merchandise items. d. Over 95 percent of our current users will prefer the redesigned site to the current site. e. Users should be able to find the “check out” page in one click no matter where they are in the site. f. If they have shopped online previously, users should be satisfied with the security of our site’s online transaction system.