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The differences among direct mapping and set-associative mapping :Direct mapping : Each line in main memory maps onto a single cache line.Set-associative : Each line in main memory maps onto a small (collection) set of cache line.Direct mapping : A memory block is mapped into a unique cache line, depending on the memory address of the respective block.Set-associative : A memory block is mapped into any of the line of a set. The set is determined by the memory address, but the line inside the set can be any one.dont knowyet
Direct mappingA given Main Memory block can be mapped to one and only one Cache Memory line.It is Simple, Inexpensive, fastIt lacks mapping flexibilityAssociative mappingA block in the Main Memory can be mapped to any line in the Cache Memory available (not already occupied)It is slow, expensiveIt has mapping flexibility
The differences among direct mapping and set-associative mapping :Direct mapping : Each line in main memory maps onto a single cache line.Set-associative : Each line in main memory maps onto a small (collection) set of cache line.Direct mapping : A memory block is mapped into a unique cache line, depending on the memory address of the respective block.Set-associative : A memory block is mapped into any of the line of a set. The set is determined by the memory address, but the line inside the set can be any one.dont knowyet
Three types of mapping procedures are there? (1) Associative Mapping-The fastest and most flexible cache organizations uses associative mapping. The associative memory stores both the address and content of memory word. This permits any location in catche to store word in main memory. (2) Direct Mapping-Associative memories are expesive compared to RAM's because of added logic associated with each cell. (3) Set Associative Mapping-It is a more general method that includes pure associative and direct mapping as special case. It is an improvement over the direct mapping organization in that each word of cache can store two or more words of memory under the same index address. Each data word is stored together with its tag and the number of tag data items in one word of cache is said to form a set. With Regards Veer Thakur Chandigarh
Advantage: Direct mapping is simple and requires less hardware, making it cost-effective. It also provides fast access to data due to its fixed mapping of blocks to cache lines. Disadvantage: Direct mapping can lead to cache conflicts, where multiple memory blocks map to the same cache line, causing performance degradation. It also has poor cache utilization compared to other mapping techniques.
Direct mapping, associative mapping, and set-associative mapping are cache mapping techniques used in computer architecture. In direct mapping, each block of main memory maps to exactly one cache line, which can lead to conflicts if multiple blocks map to the same line. Associative mapping allows any block of memory to be placed in any cache line, providing greater flexibility but requiring more complex hardware for searching. Set-associative mapping combines both methods by dividing the cache into sets, where each set can contain multiple lines, allowing a block to be placed in any line within its designated set.
Direct mapped cache is a type of cache memory organization where each block of main memory maps to exactly one cache line. This mapping is typically determined by taking the memory address and using a portion of it, usually the lower bits, to identify the specific cache line. Although it is simple and efficient, direct mapped caches can lead to a higher number of cache misses when multiple memory addresses map to the same cache line, a phenomenon known as conflict misses. As a result, performance can be impacted if the working set of data frequently overlaps in memory.
direct mapping doesn't need replacement algorithm
consider a RAM of 64 words with a size of 16 bits.Assume that this memory have a cache memory of 8 Blocks with block size of 32 bits.Draw a diagram to show the address mapping of RAM and Cache, if 4-way set associative memory scheme is used.
I didn't quite understand your question but I'll answer you anyways :P.. It's known that the main memory is much larger that the cache memory , and we need to transfer a block of instructions to the cache memory to be frequently used by the processor to improve performance and reduce time spent in fetching instructions or data ( dealing with cache memory is much faster than RAM ). for example lets say that a main memory has a 128 data blocks and you need to place them in the cache memory which consists of 32 data blocks? then you have to have sort of technique to place them or MAPPING FUNCTION. And there are plenty of 'em (four mapping techniques as far as i know) i will just mention them without getting into details: Direct mapping , fully-associative, set-associative and n-way set associative. if you need more details just ask. greetings Can you please provide some help over Direct mapping , fully-associative, set-associative and n-way set associative Thanx
Its simply done. By connecting many lines :p
The primary disadvantage of direct-mapped cache is its potential for high conflict misses. In this cache organization, multiple memory addresses can map to the same cache line, leading to frequent evictions and reloading of data even if the cache is not full. This can significantly degrade performance, especially for workloads with access patterns that repeatedly access a limited set of memory addresses. Additionally, the simplicity of direct mapping limits flexibility, as it cannot leverage more sophisticated replacement policies available in set-associative or fully associative caches.