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A computer stores images online - Edexcel - GCSE Computer Science - Question 6 - 2019 - Paper 1
Question 6
A computer stores images online. (a) An image uses 8-bit colour and is 64 pixels wide. It uses 1MB of storage. Construct an expression to calculate the height of th... show full transcript
Worked Solution & Example Answer:A computer stores images online - Edexcel - GCSE Computer Science - Question 6 - 2019 - Paper 1
Step 1
Construct an expression to calculate the height of the image in pixels.
Answer
To calculate the height of the image in pixels, we first need to determine the total number of bits in the image based on its storage size and color depth.
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Calculate total bytes: 1 MB is equivalent to:
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Calculate total bits: Since the image uses 8-bit color, the total number of bits in the image is:
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Determine the height of the image: Given that the image width is 64 pixels, the height (h) can be calculated using the formula:
Hence,
Rearranging gives:
Step 2
Describe how the operating system uses virtual memory to manage the situation.
Answer
The operating system uses virtual memory to manage the situation where the total memory demand from applications exceeds the available physical memory. Here’s how it works:
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Memory Paging: The OS divides the memory into pages and allocates a portion of the hard disk as 'swap space' for these pages. When physical RAM is full, the OS can move some inactive pages from RAM to the swap space.
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Swapping: When an application needs more memory, the OS swaps out less frequently used pages from RAM to the disk to free up space. This allows the application to run without requiring all of its data to be in the physical RAM at the same time.
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Transparency to Applications: The applications run as if they have access to a large continuous block of memory, simplifying programming. The OS abstracts the complexity of physical memory limits, allowing more applications to run concurrently.
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Performance Considerations: Although virtual memory allows more applications to run, excessive swapping can lead to performance degradation due to increased disk I/O, known as thrashing. Therefore, the OS manages the balance between virtual and physical memory carefully to maintain optimal performance.