Explain why public key encryption is more useful for securing communications on the Internet than private (shared) key encryption. 6. A certain CS professor gives 5-point quizzes that are graded on the scale 5-A, 4-B, 3-C, 2-D, 1-F, 0-F. Write a program that accepts a quiz score as an input and prints out the corresponding grade. 7. A certain CS professor gives 100-point exams that are graded on the scale 90-100:A, 80-89:B, 70- 79:C, 60-69:D, 60:F. Write a program that accepts an exam score as input and prints out the corresponding grade. 8. An acronym is a word formed by taking the first letters of the words in a phrase and making a word from them. For example, RAM is an acronym for "random access memory." Write a program that allows the user to type in a phrase and outputs the acronym for that phrase. Note: the acronym should be all uppercase, even if the words in the phrase are not capitalized. 9. Numerologists claim to be able to determine a person's character traits based on the "numeric value" of a name. The value of a name is determined by summing up the values of the letters of the name where 'a' is 1, 'b' is 2, 'c' is 3 etc., up to 'z' being 26. For example, the name "Zelle" would have the value 26 5 12 12 5 60 (which happens to be a very auspicious number, by the way). Write a program that calculates the numeric value of a single name provided as input. 10. Expand yoursolution to the previous problem to allow the calculation of a complete name such as "John Marvin Zelle" or "John Jacob Jingleheimer Smith." The total value is just the sum of the numeric value for each name. 11. A Caesar cipher is a simple substitution cipher based on the idea of shifting each letter of the plaintext message a fixed number (called the key) of positions in the alphabet. For example, if the key value is 2, the word "Sourpuss" would be encoded as "Uqwtrwuu." The original message can be recovered by "reencoding" it using the negative of the key. Write a program that can encode and decode Caesar ciphers. The input to the program will be a string of plaintext and the value of the key. The output will be an encoded message where each character in the original message is replaced by shifting it key characters in the ASCII character set. For example, if ch is a character in the string and key is the amount to shift, then the character that replaces ch can be calculated as: chr(ord(ch) + key

The table of elements should contain two columns: the first listing the elements, and the second listing the attributes that are associated with each element. The attributes should be listed one per table row, and each element name should span the rows containing its attributes. Each element and attribute name in the table should be a hyperlink to a detail page describing that element or attribute. Each detail page should use a dl style list to define the element or attribute (your description can be short?a sentence or two?but it should be accurate). The table of attributes should be similar, except that the attribute names are in the first column and each attribute name will span a set of rows containing element names associated with the attribute. All pages should have meaningful titles, and tables should include meaningful captions. (b) Modify the collection of pages in (a) to use frames. Specifically, the user should initially see a page containing three frames: upper left, lower left, and right (much like a Javadoc frames page, such as the one in Fig. 2.6). The upper left frame should contain the two-element list of two hyperlinks to the element and attribute pages. The lower left frame should initially contain the element table, but whenever the user clicks a link in the upper left frame, the lower left frame should display the appropriate table, either element or attribute. When a link is clicked in the lower left frame, the associated page should be displayed in the rightmost frame (initially, this frame should display the detail page for the first element in your element table).

[8.23] Consider a long sequence of accesses to a disk with 8 ms average seek time, 3 ms average rotational delay, and a data transfer rate of 60 Mbytes/sec. The average size of a block being accessed is 64 Kbytes. Assume that each data block is stored in contiguous sectors. (a) Assuming that the blocks are randomly located on the disk, estimate the average percentage of the total time occupied by seek operations and rotational delays. (b) Suppose that 20 blocks are transferred in sequence from adjacent cylinders, reducing seek time to 1 ms. The blocks are randomly located on these cylinders. What is the total transfer time?