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S5 ICT Paper: Data Representation, Networks and Security (100 marks)
S5 ICT – data, networks and security
S5 ICT mock: 6 questions, 24 parts, 100 marks, 75 min. Binary and hex conversion, file sizes, CPU speed, subnetting, encryption and cloud backup, with full answers.
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Paper details S5 ICT practice paper on data representation, networks and security with marking scheme
Section 1: Data representation and file size (16 marks)
Four parts, 4 marks each. Show your working.
| # | Question | Answer and marking notes |
|---|---|---|
| 1 | Convert the binary number 11011011 to a denary number. | Answer: 219. (Marking: 2 marks for place-value expansion, 2 for the result.) |
| 2 | Convert the hexadecimal number 4F to denary and to an 8-bit binary number. | Answer: denary 79, binary 01001111. (Marking: 2 marks for denary, 2 for binary.) |
| 3 | Audio is sampled at 44100 Hz, 16-bit resolution, stereo, for 180 seconds. Taking 1 MB as 1000000 bytes, what is the uncompressed file size in MB? | Answer: 31752000 bytes, about 31.75 MB. (Marking: 2 marks for samples x bits x channels, 2 for the conversion.) |
| 4 | An uncompressed image is 1024 by 768 pixels at 24-bit colour. What is its size in MiB? (1 MiB = 1048576 bytes) | Answer: 2359296 bytes, that is 2.25 MiB. (Marking: 2 marks for total pixels, 2 for the byte conversion.) |
Section 2: Computer systems and hardware (16 marks)
Four parts, 4 marks each.
| # | Question | Answer and marking notes |
|---|---|---|
| 5 | A processor runs at 3.2 GHz and needs 4.0 clock cycles per instruction on average. Find the instructions per second and express it in MIPS. | Answer: about 800000000 instructions per second, that is 800 MIPS. (Marking: 2 marks for clock divided by cycles, 2 for MIPS.) |
| 6 | A memory has 20 address lines and each location stores 1 byte. Find the number of addressable locations and the total capacity in MiB. | Answer: 1048576 locations, total capacity 1 MiB. (Marking: 2 marks for 2 to the power 20, 2 for capacity.) |
| 7 | A computer has 4 GiB of main memory. Express this capacity in bytes. (1 GiB = 1073741824 bytes) | Answer: 4294967296 bytes. (Marking: 2 marks for the conversion factor, 2 for the multiplication.) |
| 8 | Following the previous part, the processor must run 2400000000 instructions. Using the speed in the first part, how many seconds are needed? | Answer: 3.0 seconds. (Marking: 2 marks for using the rate, 2 for the division.) |
Section 3: Networks and data transmission (16 marks)
Four parts, 4 marks each. Ignore overheads.
| # | Question | Answer and marking notes |
|---|---|---|
| 9 | A 45 MB file is sent over a 128 Mbps link (1 MB is 1000000 bytes). How many seconds does it take? | Answer: 2.81 seconds. (Marking: 2 marks for converting the file to bits, 2 for dividing by the bit rate.) |
| 10 | The network 192.168.20.0 uses a /26 subnet mask. State the total addresses per subnet, the usable host addresses and the subnet mask. | Answer: 64 addresses in total, 62 usable host addresses, mask 255.255.255.192. (Marking: 2 marks total addresses, 1 usable hosts, 1 mask.) |
| 11 | Send 4 GB over a 100 Mbps link (1 GB is 1000000000 bytes). How many seconds are needed? Give the answer in minutes and seconds. | Answer: 320 seconds, that is 5 minutes 20 seconds. (Marking: 2 marks for bits, 1 for seconds, 1 for the minute form.) |
| 12 | A network carries 1000 packets per second and each packet is 1500 bytes. Find the effective throughput in Mbps and in MB/s. | Answer: 12 Mbps, that is 1.5 MB/s. (Marking: 2 marks for bits per second, 1 mark for each unit.) |
Section 4: Network security and encryption (20 marks)
Four parts, 5 marks each.
| # | Question | Answer and marking notes |
|---|---|---|
| 13 | A system requires an 8-character password from 62 possible characters (upper case, lower case and digits). Find the total number of combinations. | Answer: 62 to the power 8, that is 218340105584896 combinations, about 2.18e+14. (Marking: 3 marks for the expression, 2 for the value.) |
| 14 | An attacker can try 1000000000 combinations per second. Using the total from the first part of this section, how many days are needed to try every combination? | Answer: 218340105584896 divided by 1000000000 and by 86400, about 2.53 days. (Marking: 3 marks for dividing by the attempt rate, 2 for the day conversion.) |
| 15 | Compare the key spaces of a 128-bit and a 56-bit key. How many times larger is the 128-bit key space? Explain what this means in practice. | Answer: 2 to the power 72, about 4.72e+21 times. In practice a 56-bit key can be brute-forced by modern hardware in reasonable time, while 128-bit is far beyond reach. (Marking: 2 marks for subtracting exponents, 2 for the ratio, 1 for the meaning.) |
| 16 | In a phishing test of 500 staff, 12% clicked the fake link. Find the number who clicked and suggest one measure to reduce the risk. | Answer: 60 people. Measure: regular phishing drills and two-factor authentication. (Marking: 3 marks for the number, 2 for the measure.) |
Section 5: Cloud computing and information literacy (16 marks)
Four parts, 4 marks each.
| # | Question | Answer and marking notes |
|---|---|---|
| 17 | A cloud plan offers 2 TB of storage (1 TB is 1000000 MB) and each photo is 4 MB. How many photos can be stored? | Answer: 500000 photos. (Marking: 2 marks for converting to MB, 2 for the division.) |
| 18 | Upload 500 photos of 4 MB each with an upload bandwidth of 20 Mbps. How many seconds and minutes are needed? | Answer: 800 seconds, about 13.33 minutes. (Marking: 2 marks for the data volume, 1 for seconds, 1 for minutes.) |
| 19 | Under the 3-2-1 backup rule, how much total storage is needed for 100 GB of data, and how many copies must be kept off site? | Answer: three copies, so 300 GB in total, with 1 copy kept off site. (Marking: 1 mark for the copy count, 2 for the total, 1 for off site.) |
| 20 | Explain how to respect copyright when sharing other people work online, and how to protect your own digital footprint. | Answer: for copyright, obtain permission or use openly licensed material and credit the source; for the digital footprint, review privacy settings, avoid publishing personal data and search your own public record regularly. (Marking: 2 marks for copyright, 2 for the digital footprint.) |
Section 6: Integrated application (16 marks)
Four parts, 4 marks each.
| # | Question | Answer and marking notes |
|---|---|---|
| 21 | A school computer room has 30 computers, each drawing 250 W, used 6 hours a day for 20 days a month. Find the monthly energy use in kWh. | Answer: 900 kWh. (Marking: 1 mark for converting to kW, 2 for the hours, 1 for the multiplication.) |
| 22 | Following the previous part, if electricity costs 1.2 dollars per kWh, what is the monthly bill? | Answer: 1080 dollars. (Marking: 2 marks for using the energy figure, 2 for the calculation.) |
| 23 | Compress the uncompressed audio from the third part of Section 1 (31752000 bytes, 180 seconds) to a 128 kbps MP3. Find the compressed size, the compression ratio and the percentage saved. | Answer: 2880000 bytes; a ratio of about 11.03 to 1; about 90.93% saved. (Marking: 1 mark for the size, 2 for the ratio, 1 for the percentage.) |
| 24 | Suggest two security measures for the network in the computer room and give a reason for each. | Answer: first, enable two-factor authentication for staff accounts to cut the risk of intrusion after a password leak; second, separate the student network from the administrative network into different subnets to limit lateral movement. (Marking: 2 marks for each measure with its reason.) |
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