Memory and Primary Storage Worksheets, Questions and Revision

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GCSE · Computer Systems (Memory and Storage)

P1.2 Memory and Primary Storage

OCR J277/01 - 1.2 Memory and Storage · Calculators not allowed · about 90 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

1

Identify which type of memory is volatile, meaning its contents are lost when the power supply is removed.

A) RAM
B) ROM
C) Hard disk drive (HDD)
D) Solid state drive (SSD)

(Total for Question 1 is 1 mark)

2

Table 1 shows four statements about memory in a desktop computer. For each statement, state whether it describes RAM, ROM, or Both.

(a)Its contents are lost when the power supply is switched off.(1)

(b)It stores the start-up instructions (bootstrap program) needed when the computer is first switched on.(1)

(c)It can be read from and written to while applications are running.(1)

(d)It is a type of primary storage that the CPU can access directly.(1)

(Total for Question 2 is 4 marks)

3

Explain why a computer requires both RAM and ROM, rather than just one type of memory.

(Total for Question 3 is 3 marks)

4

Order these four memory types from fastest access speed to slowest access speed: RAM, Registers, Cache, Secondary storage (SSD).

(Total for Question 4 is 2 marks)

5

Describe the purpose of cache memory in a computer system.

(Total for Question 5 is 2 marks)

6

A gaming computer's CPU cache size is increased from 4 MB to 8 MB. Explain the likely effect this will have on the performance of the CPU.

(Total for Question 6 is 3 marks)

7

Virtual memory is a technique used by operating systems to manage limited RAM.

(a)Define the term virtual memory.(1)

(b)Explain why an operating system uses virtual memory when RAM becomes full.(3)

(Total for Question 7 is 4 marks)

8

Explain one disadvantage of a computer relying heavily on virtual memory rather than RAM.

(Total for Question 8 is 2 marks)

9

This question is about units used to measure the amount of data stored in a computer.

(a)State how many bits are in one byte.(1)

(b)State how many bytes are in one kibibyte (KiB).(1)

(c)A photo file is 2.5 MB in size. Calculate the size of the file in kilobytes (KB). Use 1 MB = 1000 KB.(1)

(d)Calculate the size of the same photo file in bytes. Use 1 KB = 1000 bytes.(1)

(Total for Question 9 is 4 marks)

10

This question is about converting between binary, denary and hexadecimal, as used to represent memory contents and addresses. Show your working for each conversion.

(a)Convert the 8-bit binary number 01011010 to denary.(2)

(b)Convert the same binary number, 01011010, to hexadecimal.(2)

(c)Convert the hexadecimal value 3F into an 8-bit binary number.(2)

(d)Convert the denary number 200 into hexadecimal.(2)

(Total for Question 10 is 8 marks)

11

This question is about the use of hexadecimal to represent memory addresses.

(a)A memory location is addressed using the hexadecimal value 2C. Calculate this address in denary.(2)

(b)State why programmers often use hexadecimal, rather than binary, when writing or reading memory addresses.(2)

(Total for Question 11 is 4 marks)

12

A laptop has 8 GB of RAM installed. Calculate the maximum number of 4 MB photo files that could be held in this RAM at one time, if no other data were stored in RAM. Use 1 GB = 1000 MB.

(Total for Question 12 is 3 marks)

13

A CPU's cache has a hit rate of 90%. During a task, the CPU makes 5000 requests for data. Calculate the number of these requests that were cache hits, and the number that were cache misses.

(Total for Question 13 is 3 marks)

14

A programmer wants to estimate how much memory (in bytes) a program will need to store some simple variables. Every INTEGER variable takes up 4 bytes and every CHAR variable takes up 1 byte.

Write an algorithm, using pseudocode, that:
- asks the user to input the number of INTEGER variables needed
- asks the user to input the number of CHAR variables needed
- calculates and outputs the total number of bytes required.

(Total for Question 14 is 5 marks)

15

A programmer writes the following algorithm to check whether some file sizes (in bytes) count as 'Large' or 'Small'.

fileSizes = [500000, 2000000, 15000000]
FOR i = 0 TO 2
    sizeInMB = fileSizes[i] / 1000000
    IF sizeInMB >= 1 THEN
        OUTPUT "Large"
    ELSE
        OUTPUT "Small"
    ENDIF
NEXT i

Complete the trace table to show the values of i, fileSizes[i] and sizeInMB, and the output produced, as the algorithm executes.

(Total for Question 15 is 4 marks)

16

A student upgrades their laptop's RAM from 8 GB to 16 GB, hoping this will make their laptop run much faster.

Discuss the likely effect of this upgrade on the laptop's performance, and explain the circumstances in which further increasing the RAM would provide little or no additional benefit.

In your answer you should refer to:
- the relationship between RAM size, secondary storage use and performance
- the role of the CPU and cache in overall performance
- the idea of diminishing returns

(Total for Question 16 is 6 marks)

17

This question is about the contents of ROM.

(a)State what type of program is typically stored in ROM in a computer system.(1)

(b)Explain why it is essential that this data is not lost when the computer's power is switched off.(2)

(Total for Question 17 is 3 marks)

18

Registers inside the CPU are much faster to access than RAM. Explain why registers cannot be used to store all of the data and instructions needed by a currently running program, instead of RAM.

(Total for Question 18 is 2 marks)

19

A processor's address bus can produce 2²⁴ different addresses, and each address refers to one byte of memory. Calculate the maximum amount of RAM, in MB, that this processor can address. Use 1 MB = 2²⁰ bytes.

(Total for Question 19 is 3 marks)

20

Laptop A and Laptop B have identical CPUs and the same amount of RAM, but Laptop A has a larger CPU cache than Laptop B.

(a)Explain, using the idea of cache hit rate, why Laptop A is likely to complete most everyday tasks faster than Laptop B.(2)

(b)Explain one situation in which Laptop A's extra cache would provide little or no performance benefit over Laptop B.(2)

(Total for Question 20 is 4 marks)

21

This question is about memory addressing.

(a)A memory address is 4 bits long. State the maximum number of unique memory locations that can be addressed.(1)

(b)A system needs to be able to address 1024 unique memory locations. Calculate the minimum number of bits required for each address.(2)

(Total for Question 21 is 3 marks)

22

Identify two units of digital storage that are larger than a gigabyte (GB). Give your answer in order, smallest to largest.

(Total for Question 22 is 2 marks)

23

State one reason why ROM is described as non-volatile memory.

(Total for Question 23 is 1 mark)

24

A tablet computer has 4 GB of RAM installed. While several apps are open, 3.2 GB of this RAM is in use. Calculate the percentage of the tablet's RAM currently in use.

(Total for Question 24 is 2 marks)

25

Explain why closing applications that are not being used can improve the performance of a computer that has a limited amount of RAM.

(Total for Question 25 is 2 marks)

Mark scheme · P1.2 Memory and Primary Storage

Question 1

B1 A only oe
Answer: A) RAM

Question 2

(a) B1 RAM
(a) Answer: RAM
(b) B1 ROM
(b) Answer: ROM
(c) B1 RAM
(c) Answer: RAM
(d) B1 Both
(d) Answer: Both

Question 3

B1 ROM stores the fixed start-up instructions/BIOS needed to boot the computer, which must not be lost when the power is off
B1 RAM is needed to temporarily store data/instructions for programs that are currently running, which can change
B1 using only ROM would mean data could not be changed while the computer runs; using only RAM would mean the start-up instructions would be lost every time the power is removed (any three of these points, max 3)
Answer: ROM holds permanent, unchanging start-up instructions that survive power loss; RAM holds changeable, temporary data for running programs. Both are needed because their properties (permanent/read-only vs changeable/read-write) are needed for different jobs.

Question 4

B1 Registers placed first (fastest) and Secondary storage (SSD) placed last (slowest)
B1 Cache placed between Registers and RAM, giving the full order: Registers, Cache, RAM, Secondary storage (SSD)
Answer: Registers, Cache, RAM, Secondary storage (SSD)

Question 5

B1 stores instructions/data that the CPU has recently used or is likely to need again soon
B1 so the CPU can access this data much faster than fetching it from (the slower) RAM each time, improving performance oe
Answer: Cache stores frequently/recently used instructions and data close to the CPU, so the CPU can retrieve it faster than from RAM, improving overall speed.

Question 6

B1 a larger cache can store more frequently/recently used instructions and data at once
B1 this increases the cache hit rate (more of the CPU's requests are found in the cache rather than needing RAM)
B1 so the CPU spends less time waiting for data from the slower RAM, increasing overall processing speed/performance
Answer: Doubling the cache size is likely to increase the cache hit rate, meaning the CPU less often has to wait for the slower RAM, so overall performance improves.

Question 7

(a) B1 an area of secondary storage (e.g. the hard disk/SSD) that is used as an extension of RAM oe
(a) Answer: An area of secondary storage used as an extension of RAM, to store data that does not fit in RAM.
(b) B1 when RAM is full, the operating system moves data that is not currently being used out of RAM and onto secondary storage (virtual memory)
(b) B1 this frees up space in RAM for the data/programs that are currently needed
(b) B1 allowing the computer to continue running programs/multitask even though there is not enough physical RAM to hold everything at once
(b) Answer: The OS swaps out unused data from RAM to secondary storage, freeing RAM space so currently needed programs/data can be loaded, allowing the system to keep running despite insufficient physical RAM.

Question 8

B1 secondary storage (disk/SSD) is much slower to access than RAM
B1 so if data has to be swapped between RAM and virtual memory very frequently, the computer's performance slows down significantly oe (thrashing)
Answer: Virtual memory is stored on much slower secondary storage than RAM, so heavy use of it (frequent swapping) makes the computer noticeably slower.

Question 9

(a) B1 8
(a) Answer: 8 bits
(b) B1 1024
(b) Answer: 1024 bytes
(c) A1 2500 (KB) cao
(c) Answer: 2500 KB
(d) A1 2 500 000 (bytes) cao, ft from (c)
(d) Answer: 2,500,000 bytes

Question 10

(a) M1 correct place values identified/summed, e.g. 64 + 16 + 8 + 2
(a) A1 90 cao
(a) Answer: 90
(b) M1 binary split correctly into nibbles: 0101 and 1010
(b) A1 5A cao
(b) Answer: 5A
(c) M1 each hex digit correctly converted to a 4-bit nibble: 3 = 0011, F = 1111
(c) A1 00111111 cao
(c) Answer: 00111111
(d) M1 200 divided by 16 giving quotient 12 and remainder 8 (or equivalent method)
(d) A1 C8 cao
(d) Answer: C8

Question 11

(a) M1 (2 x 16) + 12 shown
(a) A1 44 cao
(a) Answer: 44
(b) B1 hexadecimal numbers are shorter/use fewer digits than the equivalent binary number
(b) B1 this makes them quicker to read and write, and less prone to human error, than long strings of binary digits
(b) Answer: Hexadecimal represents the same value in far fewer digits than binary, making addresses quicker and easier for humans to read/write accurately.

Question 12

M1 8 GB converted to 8000 MB
M1 8000 divided by 4 shown (method for number of files)
A1 2000 (files) cao
Answer: 2000 files

Question 13

M1 0.9 x 5000 shown
A1 4500 cache hits cao
B1 500 cache misses (ft: 5000 - hits)
Answer: 4500 cache hits, 500 cache misses

Question 14

1 mark correct input statement that stores the number of INTEGER variables (e.g. numIntegers = input("Enter number of integer variables: "))
1 mark correct input statement that stores the number of CHAR variables
1 mark correct calculation of total bytes: (numIntegers x 4) + (numChars x 1)
1 mark total bytes correctly output, e.g. using print()
1 mark algorithm is logically complete and would run correctly overall; award marks for any correct logic and ignore minor syntax errors

Answer:

numIntegers = input("Enter number of integer variables: ")
numChars = input("Enter number of character variables: ")
totalBytes = (numIntegers * 4) + (numChars * 1)
print(totalBytes)

Question 15

B1 row i = 0: fileSizes[i] = 500000, sizeInMB = 0.5, Output = Small, all correct
B1 row i = 1: fileSizes[i] = 2000000, sizeInMB = 2, Output = Large, all correct
B1 row i = 2: fileSizes[i] = 15000000, sizeInMB = 15, Output = Large, all correct
B1 the loop counter i shown correctly incrementing 0, 1, 2 across the three rows
Answer: i=0: fileSizes[i]=500000, sizeInMB=0.5, Output=Small | i=1: fileSizes[i]=2000000, sizeInMB=2, Output=Large | i=2: fileSizes[i]=15000000, sizeInMB=15, Output=Large

Question 16

Level 1 (1-2): Basic, isolated statement(s), e.g. 'more RAM makes it faster', with little or no justification. Limited or no use of appropriate technical terms. Answer is not clearly linked to the scenario.
Level 2 (3-4): Shows some understanding of how RAM size affects performance (e.g. reduces reliance on slower virtual memory/secondary storage), with some justification. The discussion may be one-sided or not fully developed, and diminishing returns/the role of the CPU and cache may be only briefly mentioned. Some appropriate technical terms used.
Level 3 (5-6): A coherent, well-developed discussion that explains how increasing RAM reduces reliance on (slower) virtual memory up to a point, and explains that once RAM is large enough to hold everything the CPU currently needs, further increases give diminishing returns because performance is then limited by other components such as the CPU and cache. The answer is logically structured and uses appropriate technical terminology throughout.
Indicative content:
- Before the upgrade, if 8 GB of RAM was often full, the operating system would have to use virtual memory (secondary storage) to store data that did not fit in RAM
- Secondary storage (HDD/SSD) is much slower to access than RAM, so relying on virtual memory slows the computer down
- Increasing RAM to 16 GB means more data/programs can be held in RAM at once, reducing how often virtual memory is needed
- This is likely to noticeably improve performance if the laptop was previously running out of RAM
- However, if the tasks the student runs never actually needed more than 8 GB, having 16 GB gives little or no extra benefit (diminishing returns)
- Overall performance also depends on the CPU (clock speed, number of cores) and cache size, not just the amount of RAM
- If the CPU itself is slow, or the cache is small, adding more RAM will not fix these bottlenecks
- Therefore performance gains from adding RAM depend on what was actually limiting performance beforehand

Question 17

(a) B1 the BIOS / bootstrap program / start-up instructions / firmware oe
(a) Answer: The BIOS/bootstrap program (start-up instructions/firmware).
(b) B1 this program must run every time the computer starts, before the operating system has been loaded from secondary storage
(b) B1 if it was lost, the computer would not be able to begin starting up / load the operating system at all
(b) Answer: The start-up program is needed at every boot, before the OS is available; without it stored permanently, the computer could never start.

Question 18

B1 registers have an extremely small capacity (each register can typically only hold one value/a very small amount of data)
B1 so RAM (with a much larger capacity) is needed to hold the full program and its data, with only small amounts moved into registers when the CPU needs them
Answer: Registers can hold only tiny amounts of data each, so RAM (far larger capacity) is needed to store the whole running program, with data moved into registers only as needed.

Question 19

M1 2²⁴ evaluated as 16 777 216 (bytes)
M1 16 777 216 divided by 2²⁰ (1 048 576) shown, or equivalent use of index laws (2²⁴ / 2²⁰ = 2⁴)
A1 16 (MB) cao
Answer: 16 MB

Question 20

(a) B1 the larger cache can hold more of the instructions/data the CPU is currently using, increasing the cache hit rate
(a) B1 so Laptop A's CPU has to wait for the slower RAM less often, allowing it to complete tasks faster
(a) Answer: Laptop A's larger cache gives a higher hit rate, so its CPU waits for RAM less often, completing tasks faster.
(b) B1 identifies a scenario where the task's working data already fits entirely within Laptop B's (smaller) cache, e.g. a simple task using very little data
(b) B1 in this case both laptops would already have a similarly high hit rate, so Laptop A's extra cache capacity would rarely be used / would give no noticeable speed advantage
(b) Answer: If the task's data already fits within the smaller cache, both laptops achieve a similarly high hit rate, so the extra cache in Laptop A gives no real benefit.

Question 21

(a) B1 16 cao
(a) Answer: 16
(b) M1 recognises that 2ⁿ must be greater than or equal to 1024
(b) A1 10 cao
(b) Answer: 10 bits

Question 22

B1 Terabyte (TB)
B1 Petabyte (PB), given after Terabyte
Answer: Terabyte (TB), then Petabyte (PB)

Question 23

B1 its contents are not lost / are retained when the power supply is switched off oe
Answer: Its contents are retained even when the power is switched off.

Question 24

M1 3.2 / 4 shown (or equivalent method)
A1 80% cao
Answer: 80%

Question 25

B1 closing unused applications frees up space in RAM
B1 so there is more room for the apps/data that are actually being used, meaning the operating system needs to use (slower) virtual memory less often, improving performance
Answer: Closing unused apps frees RAM space, reducing the need for the OS to use slower virtual memory, which improves performance.

Memory and Primary Storage - Worksheets, Questions and Revision

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