Assess your understanding of memory access time, performance optimization techniques, and key concepts such as latency, caching, and memory hierarchies. This quiz is designed to reinforce the fundamentals of minimizing memory delays and improving computer system performance.
Which component of memory access time refers specifically to the delay between requesting data and its arrival, regardless of transfer speed?
Explanation: Latency refers to the time delay between a data request and the start of data transfer, regardless of how fast data moves afterward. Bandwidth measures how much data can be transferred per unit of time, not the delay. Throughput is the total work completed per time, and parity is related to error checking, not access time. Only latency captures the initial wait for data.
In a computer's memory hierarchy, which level typically offers the fastest access time but the smallest storage capacity?
Explanation: CPU registers provide the fastest possible access for the processor but hold only a tiny amount of data. Main memory is slower and larger, solid-state drives are used for non-volatile storage, and disk cache manages data for disks, which are slower. Only registers combine the fastest speed with minimal size.
When a computer program repeatedly accesses the same few memory addresses, which technique helps reduce average memory access time?
Explanation: Caching stores recently used data in faster memory so repeated access is quicker. Paging handles memory allocation but does not speed up access to a specific address, swapping manages memory for inactive processes, and hashing helps with data lookup, not memory speed. Caching is the correct optimization.
Which event forces the processor to fetch data from slower main memory, increasing the total memory access time?
Explanation: A cache miss occurs when needed data is not found in the cache, causing the processor to access slower main memory. A page fault involves virtual memory, cache hit means data is already in the cache, and a bit flip is a data error. Only cache misses directly add to access delay in this context.
What memory optimization technique arranges related data items close together to increase the chance of accessing them quickly during a loop?
Explanation: Data locality takes advantage of temporal and spatial patterns by grouping frequent or consecutive memory accesses closely, speeding up access within loops. Data fragmentation scatters items, increasing access time. Address randomization is used for security. Swap partitions manage virtual memory swaps. Only data locality improves sequential access times.
If your computer's RAM has a latency of 15 nanoseconds, what does this value represent?
Explanation: Latency measures the delay before data from RAM becomes available after a request. It does not define how much data RAM stores, which relates to capacity. Disk speed is unrelated to RAM latency. The memory address bus size determines the range of addresses, not the timing of access.
Which strategy is used by some CPUs to load data into the cache before it is actually needed by running programs, potentially reducing memory access time?
Explanation: Prefetching anticipates which data will be needed soon and loads it into cache ahead of time, reducing potential wait times. Buffering temporarily holds data during transfers but does not anticipate needs. Mirroring involves copying data for redundancy, and throttling slows processes to avoid overloading. Prefetching addresses proactive cache loading.
In which cache write policy is data written to main memory only when the cache line is replaced, rather than every time it is updated?
Explanation: Write-back cache delays writing to main memory until the cache line is replaced, reducing memory traffic. Write-through updates memory on every cache update, increasing consistency but also access times. Write-ahead is used for logs, not cache memory, and write-miss is not a standard cache policy.
What happens to memory access time if a program heavily relies on virtual memory and causes frequent page faults?
Explanation: Frequent page faults stall the program while data is retrieved from slow storage, greatly increasing memory access time. Slight decreases are unrealistic as faults always cause delays. Access time cannot remain unchanged or negligible since disk or SSD accesses introduce major latencies.
How does increasing a processor's cache size typically affect average memory access time for most programs?
Explanation: A larger cache can store more frequently accessed data, reducing the number of cache misses and improving average access times. Increasing cache size does not increase access time or corrupt memory. While extremely large or poorly managed caches could have diminishing returns, in most cases, increased cache size improves performance.