Data Storage - Worksheet (gr 10)

1. The following 2 pictures are images of the letter ‘R’ stored as bitmap files:

(a) Why is picture X fuzzy? …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. (b) Even the sharp image in picture Y would become fuzzy if enlarged. Why would this happen? …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. (c) Name an output device that makes use of this imaging method. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. (d) State a drawback of storing sharp quality bitmap image files. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. 2. Identify whether the four statements about file compression are correct by writing TRUE or FALSE in the following table.

3. a) A microprocessor regularly samples the output, X. Each sample value is stored in an 8-bit register as shown below. One bit of this register is reserved as a parity bit. Five consecutive output values of 1 indicate a fault condition. Identify which of the following registers shows a fault condition.

b) When eight bytes of data have been collected, they are transmitted to a computer 100 km away. Parity checks are carried out to identify if the data has been transmitted correctly. The system uses even parity and column 1 is the parity bit. The eight bytes of data are sent together with a ninth parity byte:

4.

Check digits are used to ensure the accuracy of entered data. A 7-digit number has an extra digit on the right, called the check digit.

The check digit is calculated as follows: • each digit in the number is multiplied by its digit position • the seven results are then added together • this total is divided by 11 • the remainder gives the check digit (if the remainder = 10, the check digit is X) (a) Calculate the check digit for the following number. Show all your working.

5. Nigel wants to send a large text file electronically to Mashuda. (a) Describe how the size of the text file can be reduced. …………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. …………………………………………………………………………………………………………….. (b) This file will be transmitted to Mashuda as an email attachment. Mashuda then stores it on her computer. Explain how checksums can be used to verify that the file has not been corrupted during transmission or data storage. …………………………………………………………………………………………………………….. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. …………………………………………………………………………………………………………….. 6. Two types of compression are lossy and lossless. Choose the most suitable type of compression for the following and explain your choice. (i) Downloading the code for a computer program: Type of compression.......................................................................................................... Explanation........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... (ii) Streaming a video file: Type of compression.......................................................................................................... Explanation........................................................................................................................ ............................................................................................................................. .............. ...........................................................................................................................................

7.

Explain how ARQ is used in error detection. ............................................................................................................................. .............. ............................................................................................................................. .............. ........................................................................................................................................... ............................................................................................................................. .............. ...........................................................................................................................................