Look inside the OCR GCSE Computer Science guide (J277)

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Look inside the OCR GCSE Computer Science guide

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OCR · GCSE · J277
Computer Science
Active Recall Guide
740 questions
Computer ScienceContents
Contents
11 topics, 46 subtopics
  1. Systems Architecture46
  2. Memory and Storage143
  3. Computer Networks, Connections and Protocols99
  4. Network Security51
  5. Systems Software45
  6. Ethical, Legal, Cultural and Environmental Impacts of Digital Technology64
  7. Algorithms81
  8. Programming Fundamentals99
  9. Producing Robust Programs48
  10. Boolean Logic32
  11. Programming Languages and Integrated Development Environments32
ii
Memory and StorageQuestions
Memory and Storage
RAM, ROM, cache and virtual memory
  1. What is primary storage?
  2. Why does a computer need primary storage as well as secondary storage?
  3. Which types of memory make up primary storage?
  4. What does RAM stand for, and what is its purpose?
  5. What does ROM stand for, and what is its purpose?
  6. What does it mean to say that RAM is volatile?
  7. Why must ROM be non-volatile?
  8. State three differences between RAM and ROM.
  9. A student is typing an essay when the power fails. Why is the unsaved work lost?
12
Memory and StorageAnswers
Answers
RAM, ROM, cache and virtual memory
  1. Primary storage is the memory that the CPU can access directly. Primary storage holds the data and instructions currently in use.
  2. The CPU needs very fast access to the programs and data it is running. Secondary storage is far too slow for the CPU to work from directly.
  3. Primary storage is usually made up of RAM and ROM. Cache is also a form of primary storage.
  4. RAM stands for random access memory. RAM holds the operating system, programs and data that are currently in use.
  5. ROM stands for read-only memory. ROM holds the start-up instructions, such as the BIOS, that get the computer running when it is switched on.
  6. Volatile memory loses its contents when the power is switched off. RAM needs a constant power supply to keep its data.
  7. The start-up instructions must be available every time the computer is switched on. Non-volatile memory keeps its contents without power.
  8. RAM is volatile, but ROM is non-volatile. RAM can be read and written, while ROM can normally only be read. RAM has a much larger capacity than ROM.
  9. The unsaved essay was held only in RAM. RAM is volatile, so its contents disappear as soon as the power is cut.
13
Systems SoftwareQuestions
Systems Software
Peripheral, user and file management
  1. What is a peripheral?
  2. What is a device driver?
  3. Why does an operating system need device drivers?
  4. A new printer is connected but will not print. What is the most likely software cause?
  5. Why must data transfer between peripherals and the processor be managed?
  6. How does the operating system stop a slow printer from holding up the CPU?
  7. What does user management involve?
  8. What are access rights on a shared computer?
  9. How does user management help keep a computer secure?
34
Systems SoftwareAnswers
Answers
Peripheral, user and file management
  1. A peripheral is an input, output or storage device connected to a computer, such as a printer, keyboard or webcam.
  2. A device driver is software that lets the operating system communicate with a particular hardware device. The driver translates the OS's general instructions into commands the device understands.
  3. Every model of hardware works differently, and the OS cannot know how to control them all. A driver lets the OS use a device through one standard set of instructions.
  4. The printer's device driver is probably missing, out of date or incorrect. Without the right driver the OS cannot send the printer commands it understands.
  5. Peripherals work far more slowly than the CPU, and several may need attention at once. The OS controls the order and timing of transfers so that no data is lost.
  6. The OS stores the document in a buffer, an area of memory that feeds data to the printer. The CPU carries on with other work while the printer takes the data at its own speed.
  7. The OS creates and deletes user accounts, each protected by a username and password. The OS also controls what each user is allowed to access.
  8. Access rights are permissions that set which files, folders and programs each user may open or change. An administrator can grant or remove access rights for each account.
  9. The OS requires a username and password before anyone can use the system. Access rights then stop ordinary users from changing system settings or other people's files.
35
Producing Robust ProgramsQuestions
Producing Robust Programs
Defensive design, input validation and authentication
  1. What is defensive design?
  2. What does anticipating misuse involve?
  3. Give three ways a user might misuse a program that asks for their age.
  4. What is input validation?
  5. What does a range check test?
  6. What do a presence check and a length check test?
  7. What do a type check and a format check test?
  8. Which validation check does if password.length < 8 then print("Too short") endif carry out?
  9. Why can validation not guarantee that data is correct?
56
Producing Robust ProgramsAnswers
Answers
Defensive design, input validation and authentication
  1. Defensive design means planning a program so it copes with every likely input and with misuse. The program should keep working and stay secure.
  2. A programmer predicts how users might misuse the program, by mistake or on purpose. The code is then written to handle each case safely.
  3. A user might leave the input blank. A user might type letters such as "ten". A user might enter an impossible value such as −5 or 250.
  4. Input validation is an automatic check that data follows set rules before the program accepts it. Data that fails the check is rejected and the user is asked again.
  5. A range check tests that a value lies between a lowest and a highest limit. An example is a percentage that must be from 0 to 100.
  6. A presence check makes sure a field has not been left empty. A length check makes sure the input has an allowed number of characters, such as at least 8.
  7. A type check makes sure the input is the right data type, such as a whole number. A format check makes sure the input follows a pattern, such as DD/MM/YYYY.
  8. The code carries out a length check. Any password with fewer than 8 characters is rejected.
  9. Validation checks only that data is sensible and follows the rules. A user who types 15 instead of 16 as their age still passes a range check.
57
Keep going
740
questions
46 subtopics

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740 questions
Across 46 subtopics, every one of them from specification J277.
One PDF
Print it, or work from a screen with a notebook beside you.
Answers after, not beside
Covering the answers is a matter of not turning the page, which is what makes the closed-book pass possible.

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

  1. Step 1 · Closed book

    Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.

  2. Step 2 · Open book

    Go back to the top. Read each printed answer and write it out in full, including the ones you had right.

  3. Step 3 · Closed book again

    Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.

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