# Assignment 4

#1. How many cells can be in a computer's main memory if each cell's address can be represented by two hexadecimal digits? What if four hexadecimal digits are used? Explain your answer.

Answer:

Hexadecimal digits is a base 16 number system and it ranges between 0 and F i.e. 0 - 9 and A - F (10 -15). (Table 1 below shows binary, decimal and hexadecimal representation). Two hexadecimal digits will be between 00 and FF and this will make up to 256 cells i.e. 0 – 255 (16 bits) and for four hexadecimal digits will be between 0000 – FFFF and this makes up to 65536 cells i.e. 0 – 65535 (32 bits).

BINARY NUMBERS| DECIMAL NUMBERS| HEXADECIMAL NUMBERS|

0000| 0| 0|

0001| 1| 1|

0010| 2| 2|

0011| 3| 3|

0100| 4| 4|

0101| 5| 5|

0110| 6| 6|

0111| 7| 7|

1000| 8| 8|

1001| 9| 9|

1010| 10| A|

1011| 11| B|

1100| 12| C|

1101| 13| D|

1110| 14| E|

1111| 15| F|

Table 1: Decimal and hexadecimal representation

#2. Suppose that only 50GB of your personal computer’s 120GB hard-disk drive is empty. Would it be reasonable to use CDs to store most of the material you have on the drive as a backup? What about DVDs? Explain your answer.

Answer:

With 120GB of storage and 50GB space free that amounts to 70GB of data to back up, the maximum a CD can take is 700MB (0.7GB) that amounts to 100 CDs. The size of an average DVD-R is about 4.7GB this will make up to 15 DVDs and this makes a lot sense than using 100 CDs.

#3. Suppose three values (x, y, and z) are stored in a machine's memory. Describe the sequence of events (loading registers from memory, saving values in memory, and so on) that lead to the computation of x + y + z. How about (2x) + y?

Answer:

I. To compute x + y + z, each of the values must be retrieved from memory and placed into the register, the sum of x and y must be computed placed into the registry and the value of the sum must be added to z and...

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