Worksheet

F9.7 Secondary storage

Logic and computer systems · GCSE · OCR J277 1.2.2, AQA 8525 3.4.5, Edexcel 1CP2 3.1.2 · about 15 min

What this lesson is about

Magnetic, optical, solid state and cloud storage, and choosing between them.

• Why secondary storage?
• Three technologies
• Choosing storage
• Cloud storage
• Speed matters too

Questions 6 marks in all

1. [1 mark]Why do computers need secondary storage?

   1. AIt keeps programs and files when the power is off
   2. BIt is faster than RAM
   3. CThe CPU runs programs directly from it
   4. DIt holds the boot program

2. [1 mark]Which storage suits a robot that vibrates across a mat?

   1. ASolid state, because it has no moving parts
   2. BA hard disk, because it has high capacity
   3. COptical, because discs are cheap
   4. DMagnetic tape, because it is reliable

3. [1 mark]How does optical storage read data?

   1. AA laser reads pits and flat areas on a disc
   2. BA head reads magnetised areas
   3. CElectrical charges are read from chips
   4. DA camera photographs the disc

4. [1 mark]What is an advantage of a hard disk over an SSD?

   1. ALower cost per gigabyte
   2. BFaster access
   3. CNo moving parts
   4. DLighter

5. [1 mark]What is a drawback of cloud storage?

   1. AIt needs an internet connection
   2. BFiles cannot be shared
   3. CIt cannot be reached from a phone
   4. DIt has a fixed, small capacity

6. [1 mark]Copying a 3000 MB file at 150 MB per second takes how many seconds?

The task: the storage chooser

Write choose(needed_gb, no_moving_parts). It returns the name of the cheapest device in devices whose capacity is at least needed_gb, and which has no moving parts if no_moving_parts is True. A device's price in pence is its capacity times its pence per GB. Print one line for each job in jobs, in the form robot logs: SD card.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

# name, capacity in GB, pence per GB, has moving parts
devices = [
    ("hard disk", 2000, 2, True),
    ("SSD", 1000, 6, False),
    ("SD card", 256, 10, False),
    ("Blu-ray", 50, 4, True),
]
# job, GB needed, needs no moving parts
jobs = [("robot logs", 64, True), ("school backups", 1500, False), ("video editing", 500, True), ("film archive", 40, False)]

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/f9-7-secondary-storage/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Add a reading speed to each device, and let choose require a minimum speed.
2. Add magnetic tape: 12000 GB at 0.5 pence per GB. Which jobs change?
3. Write three sentences recommending storage for a school trip camera, using three different characteristics.