AP Computer Science Principles Unit 2

What is the best explanation for why digital data is represented in computers in binary?

• The binary number system is the only system flexible enough to allow for representing data other than numbers.

• It's easier, cheaper, and more reliable to build machines and devices that only have to distinguish between binary states.

• It typically takes fewer digits to represent a number in binary when compared to other number systems (for example, the decimal number system)

• It's impossible to build a computing machine that uses anything but binary to represent numbers

Which of the following is true about the way digital data is transmitted on the Internet?

• Bit-rate (bandwidth) is the time elapsed between the transmission and receipt of a piece of digital data.

• Latency is the amount of data (measured in bits) that can be sent in a fixed amount of time.

• Digital data can only be transmitted between two devices when they are physically connected to one another (for example by a copper wire)

• Two devices must communicate using the same bit-rate to successfully send and receive digital data.

Two students have developed a protocol in which they send 4-bit messages to each other. They decide to modify their protocol to start sending 8-bit messages instead. How many more values can be represented in an 8-bit message than a 4-bit message?

• 2¹ = 2 times as many values

• 2²= 4 times as many values

• 2³ = 8 times as many values

• 2⁴ = 16 times as many values

Under which of the following conditions is it most beneficial to use a heuristic approach to solve a problem?

• When the problem can be solved in a reasonable time and an approximate solution is acceptable

• When the problem can be solved in a reasonable time and an exact solution is needed

• When the problem cannot be solved in a reasonable time and an approximate solution is acceptable

• When the problem cannot be solved in a reasonable time and an exact solution is needed

The colors of the pixels in a digital image are often represented by red, green, and blue values between 0 and 255 (an RGB triplet). A photographer is manipulating a digital image to lighten it because all of the RGB values in the image are less than 100, making it very dark. He does this by adding 20 to the R, G, and B values of each pixel, then overwriting the original image. What type of transformation is the photographer using on the digital image?

• Lossless transformation

• Lossy transformation

• Multiband transformation

• Chrome Sampling transformation

Which of the following is a true statement about data compression?

• Data compression is only useful for files being transmitted over the Internet.

• Regardless of the compression technique used, once a data file is compressed, it cannot be restored to its original state.

• Sending a compressed version of a file ensures that the contents of the file cannot be intercepted by an unauthorized user.

• There are trade-offs involved in choosing a compression technique for storing and transmitting data.

A video-streaming Web site uses 32-bit integers to count the number of times each video has been played. In anticipation of some videos being played more times than can be represented with 32 bits, the Web site is planning to change to 64-bit integers for the counter. Which of the following best describes the result of using 64-bit integers instead of 32-bit integers?

• 2 times as many values can be represented.

• 32 times as many values can be represented.

• 2^32 times as many values can be represented.

• 32^2 times as many values can be represented.

Select the answer that lists the units of bytes in ascending order (from smallest to largest)

• gigabyte, megabyte, terabyte

• megabyte, terabyte, kilobyte

• gigabyte, terabyte, megabyte

• kilobyte, gigabyte, terabyte

An artist makes an RGB raster image in which each pixel color is encoded with 12-bits --- 4 bits each for red, green and blue.

Which of the following correctly shows the hexadecimal value for Red as a 12-bit representation.

• F00

• 00F

• FF00

• FF0000

A compression scheme for long strings of bits called run-length encoding is described as follows:

Rather than record each 0 and 1 individually, instead record "runs" of bits by storing the number of consecutive 1s and 0s that appear.

Since it's binary, any run of 0s must be followed by a run of 1s (even if the run is only 1-bit long) and vice versa. Thus, you can store a list of small numbers that represents the alternating runs of 0s and 1s. The image above is an example:

To uncompress the data back into its original binary state, you simply reverse the process. This technique is an example of what type of compression?

• Lossy compression

• Lossless compression

• Fast Fourier Transform compression

• Tailored compression