Last updated: $Date: 2007/01/09 14:53:57 $
Perform Some Calculations
First, let's look at the specification for a computer system that you might consider buying:
Processor type: Intel Core
Processor speed: 3 GHz
Hard drive: 80 GB, 10 ms access time
RAM: 512 MB
Additional peripherals: CD-RW
1. If you buy some 640 MB CD-R disks, how many would you need to back up a full hard drive once (assume no compression)? At 7 cents per disk, how much would a full backup cost? At 10 minutes per disk, 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 stored for all 295 million people in the United States
Name: 40 characters
Phone Number: 10 characters
Library Card Number: 9 characters
Unpaid Fines: one 4-byte number
Assume that each character is stored in one byte.
2. Would all of this 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. Assume that you access the data in a random order, and that you start a new disk access for each person. How long would it take to add up the library fines for all 295 million people? Could this be done in a second? In a minute? In an hour? In a day? In a month? In a year?
Assume for the sake of comparison that all of this data could fit in RAM (it won't; you should convince yourself of that).
4. How long would it take the processor to perform 295 million additions if it can perform one addition instruction for every two clock cycles? Could this be done in a second? In a minute? In an hour? In a day? In a month? In a year?
From these answers, you should be able to conclude that the processor is much faster than the hard drive. Review your notes and read the section in the book about "virtual memory". Think about how virtual memory helps to accommodate this mismatch.
Now let's see how long it would take to move the bits around.
5. How long would it take to move the contents of your entire hard drive to your friend's computer in California over a modem? Over DSL? Over a dedicated T1 line? Overnight mail?
Last updated: $Date: 2007/01/09 14:53:57 $