University of Maryland, College of Information Studies

LBSC 690: Assignment #1

This assignment is due to the TA by email before the start of the class session indicated on the syllabus. Please put "LBSC 690 assignment #1" in the subject line of your message. Either type your answers in the message body or attach a document that contains the answer. Show your work, as it may provide an opportunity to receive partial credit. Receipt of all email will be acknowledged within 24 hours.

Consider the specifications of a computer system that you might consider buying:

Processor type: Intel Core 2 Duo
Processor speed: 2.5 GHz
Hard drive: 200 GB, 10 ms access time
RAM: 2 GB, 50 ns access time
Peripherals: DVD-RW

To simplify calculations, you may assume that 1 megabyte is 1,000,000 (one million) bytes, 1 gigabyte is 1,000,000,000 (one billion) bytes, etc. (or you may use the exact values if you prefer).

Answer the following questions:

  1. If you buy some 4.7 GB DVDs, how many would you need to back up a full hard drive to DVDs (assuming no compression)? At 30 cents per DVD, how much would a full backup cost? At 10 minutes per DVD, how long would a full backup take?

    Now let's see how much stuff that hard drive can hold. Assume you have access to the following information for all 300 million people in the United States:

    Name: 40 characters
    Phone Number: 10 characters
    SSN: 9 characters
    taxes owed: one four-byte number

    Assume that each character is stored in one byte.

  2. Would all of these data fit on the hard drive of the computer described above? If not, how big a hard drive would you need? If so, what fraction of the disk would this fill?

    Now let's see how long it would take to read that much data off the disk. Assume you have a hard drive large enough to store all the data.

  3. Suppose you wanted to add up the taxes owed by all 300 million people. Assume that you access the data in a random order, and that you start a new disk access for each person (the specifications above provided the latency of disk access). How long would it take to access all the data? Could this be done in a second? In a minute? In an hour? In a day? In a month? In a year?

    Now assume instead for the sake of comparison that all of this data could fit in RAM.

  4. How long would it take to access all the data from RAM? The specifications above included the latency of RAM access. Could this be done in a second? In a minute? In an hour? In a day? In a month? In a year?

    5. Comparing those results, ...

  5. Which is faster, the RAM or the hard disk?

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