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GCSE Computer Science · 1.2.1

Primary Storage: RAM, ROM and Virtual Memory

Section A: 10 multiple choice questions, 10 marks. Section B: 5 written questions, 18 marks. Total 28 marks.

Name

Class

Date

Mark  / 28

Section A

Circle the letter of the correct answer. One mark each.

  1. 1Which statement about RAM is correct?1
    1. AIt is read only
    2. BIt is a type of secondary storage
    3. CIt is non volatile and holds the boot program
    4. DIt is volatile and holds programs and data currently in use
  2. 2Why does a computer need ROM as well as RAM?1
    1. AROM is faster than RAM
    2. BROM has a larger capacity than RAM
    3. CRAM cannot be written to
    4. DRAM is volatile, so at switch on it is empty and cannot hold the start up instructions
  3. 3What happens immediately after the boot program in ROM completes its hardware checks?1
    1. AThe CPU shuts down
    2. BThe operating system is copied from secondary storage into RAM
    3. CVirtual memory is disabled
    4. DThe operating system is copied into ROM
  4. 4Virtual memory is best described as:1
    1. AAn area of secondary storage used as if it were RAM when RAM is full
    2. BA faster form of cache
    3. CExtra RAM chips added to the motherboard
    4. DMemory built into the CPU
  5. 5Why does heavy use of virtual memory slow a computer down?1
    1. AThe operating system stops multitasking
    2. BSecondary storage is much slower than RAM, so constant swapping wastes time
    3. CThe RAM is physically removed
    4. DThe CPU clock speed is reduced
  6. 6A user complains that their computer becomes very slow when many applications are open. What is the most effective upgrade?1
    1. AInstall a larger monitor
    2. BInstall a faster network card
    3. CInstall more RAM
    4. DInstall more ROM
  7. 7Which of these is non volatile?1
    1. AROM
    2. BCache
    3. CRAM
    4. DRegisters
  8. 8Where must a program be before the CPU can execute it?1
    1. AIn RAM
    2. BOn the hard disk
    3. CIn ROM
    4. DIn the swap file
  9. 9Which is the correct ordering from fastest to slowest?1
    1. ARAM, registers, cache, secondary storage
    2. BCache, registers, secondary storage, RAM
    3. CSecondary storage, RAM, cache, registers
    4. DRegisters, cache, RAM, secondary storage
  10. 10Disk thrashing occurs when:1
    1. AA hard disk is physically damaged
    2. BThe CPU overheats
    3. CThe system spends more time swapping data between RAM and disk than doing useful work
    4. DToo many files are deleted at once

Section B

Answer in the space provided. The number of marks tells you how many separate points to make.

  1. 1StateState two differences between RAM and ROM.2
  2. 2ExplainExplain the purpose of ROM in a computer system.3
  3. 3ExplainExplain what virtual memory is and describe how it is used when a computer runs out of RAM.4
  4. 4ExplainA laptop with 4 GB of RAM becomes very slow when the user has several applications open at once. Explain why this happens and recommend a solution.6
  5. 5DescribeDescribe the role of primary storage in a computer system.3

Mark scheme

Section A

1D2D3B4A5B6C7A8A9D10C

Section B

1 State two differences between RAM and ROM. 2

One mark for each of the following, to a maximum of 2.

  • RAM is volatile while ROM is non volatile
  • RAM can be read from and written to, ROM is read only in normal use

Model answer. RAM is volatile, meaning its contents are lost when the power is switched off, whereas ROM is non volatile and keeps its contents. RAM can also be both read from and written to during normal operation, while ROM is read only in normal use.

2 Explain the purpose of ROM in a computer system. 3

One mark for each of the following, to a maximum of 3.

  • Holds the boot program or BIOS
  • It is non volatile so the instructions are still present when the computer is switched on
  • The boot program checks hardware and loads the operating system from secondary storage into RAM

Model answer. ROM holds the bootstrap program, sometimes called the BIOS, which is the set of instructions the computer runs the moment it is switched on. ROM is used because it is non volatile, so unlike RAM its contents survive the computer being powered down and the instructions are guaranteed to be present at start up. The boot program checks that the hardware is working, then locates the operating system in secondary storage and copies it into RAM so that the CPU can run it.

3 Explain what virtual memory is and describe how it is used when a computer runs out of RAM. 4

One mark for each of the following, to a maximum of 4.

  • Virtual memory is an area of secondary storage used as if it were RAM
  • Used when RAM is full and more space is needed
  • Data not being used recently is moved from RAM out to the swap file
  • It is swapped back into RAM when needed again

Model answer. Virtual memory is an area of secondary storage, such as a region of the hard disk or SSD known as the swap file, that the operating system uses as though it were additional RAM. It is used when RAM becomes full but another program or piece of data needs to be loaded. The operating system identifies data in RAM that has not been accessed recently and moves it out to the swap file, freeing physical RAM for the new data. If the data that was moved out is needed again later, it is swapped back into RAM, which may require moving something else out to make room.

4 A laptop with 4 GB of RAM becomes very slow when the user has several applications open at once. Explain why this happens and recommend a solution. 6

One mark for each of the following, to a maximum of 6.

  • 4 GB of RAM fills up when several applications are open
  • The operating system starts using virtual memory on secondary storage
  • Data is repeatedly swapped between RAM and secondary storage
  • Secondary storage is far slower to access than RAM
  • The CPU spends time waiting rather than executing instructions, which the user experiences as slowdown
  • Recommends installing more RAM, so fewer programs need to be swapped out

Model answer. With only 4 GB of RAM, opening several applications at once quickly fills the available physical memory. Once RAM is full the operating system falls back on virtual memory, which is an area of the laptop's secondary storage used as if it were RAM. Data belonging to programs that have not been used recently is written out to the swap file, and when the user switches back to those programs that data has to be read back into RAM again, usually forcing something else out. Because secondary storage is thousands of times slower to access than RAM, each of these swaps takes a substantial amount of time, and the CPU sits waiting for data instead of executing instructions. When it happens continuously it is known as disk thrashing, and the user experiences it as severe slowdown. The most effective solution is to install more RAM, for example upgrading to 16 GB, because all the open applications can then be held in physical memory at once and swapping is largely eliminated. Replacing a mechanical hard disk with an SSD would reduce the penalty of each swap, but it treats the symptom rather than the cause.

5 Describe the role of primary storage in a computer system. 3

One mark for each of the following, to a maximum of 3.

  • Primary storage is directly accessible by the CPU
  • It holds the data and instructions currently in use
  • Programs are copied from secondary storage into primary storage before they can be executed

Model answer. Primary storage is the memory that the CPU is able to access directly, and it holds the data and instructions that are currently being used, including the operating system and any programs the user has open. The CPU cannot execute a program directly from secondary storage, so when a program is opened it is first copied from secondary storage into primary storage, and the CPU then fetches its instructions from there during the fetch decode execute cycle.