Cache memory
- 3. Cache memory is a small-sized type of volatile computer memory that provides high-speed data access to a processor and stores frequently used computer programs, applications and data. It stores and retains data only until a computer is powered up.
- 5. Logical cache (virtual cache) Stores data using virtual addresses Processor accesses cache directly, not thorough physical cache Physical cache Stores data using main memory physical addresses
- 9. Fastest Cache memory Ranges in size from 8KB to 64KB internal cache or primary cache Larger but slower in speed than L1 cache. Reduce the time needed to access data Comes between L1 and RAM(processor-L1-L2-RAM)
- 10. Memory cache that is built into the motherboard Typically faster than the system’s main memory Having more than 3 MB of storag
- 12. Cache Referenc ed By CPU Contents Of Main Memory Cache mapping is the method by which the contents of main memory are brought into the cache and referenced by the CPU. There are 3 types of cache mapping method: 1.Direct Mapping 2. Associative Mapping 3. Set Associative Mapping
- 13. Each location in RAM has one specific place in cache where the data will be held. Consider the cache to be like an array. Part of the address is used as index into the cache to identify where the data will be held. Since a data block from RAM can only be in one specific line in the cache, it must always replace the one block that was already there. There is no need for a replacement algorithm.
- 14. Direct Mapping - Advantages The tag memory is much smaller than in associative mapped cache. No need for an associative search, since the slot field is used to direct the comparison to a single field
- 15. Direct Mapping – Disadvantages Every memory reference will result in a miss, which will cause an entire block to be read into the cache even though only a single word is used.
- 16. Sadi Mohammed Omi ID: 172-15-9665
- 17. A main memory block can load into any line of cache. Memory address is interpreted as tag and word Tag uniquely identifies block of memory Every line’s tag is examined for a match Cache searching gets expensive
- 19. Any main memory block can be placed into any cache slot. How irregular the data and program references are, if a slot is available for the block, it can be stored in the cache
- 20. Hardware overhead needed for cache bookkeeping. There must be a mechanism for searching the tag memory in parallel.
- 21. Md Robin Hossain ID: 172-15-9910
- 22. Cache is divided into a number of sets. Each set contains a number of lines A given block maps to any line in a given set e.g. Block B can be in any line of set i 2 way associative mapping A given block can be in one of 2 lines in only one set
- 24. The tag memory increases only slightly from the direct mapping and only two tags need to be searched for each memory reference. The set-associative cache is widely used in today’s microprocessors
- 25. Md Mahfuzar Rahman ID: 172-15-9619
- 26. When a cache miss occurs, data is copied into some location in cache With Set Associative or Fully Associative mapping, the system must decide where to put the data and what values will be replaced. Cache performance is greatly affected by properly choosing data that is unlikely to be referenced again.
- 27. When memory write operations are performed, CPU first writes into the cache memory. These modifications made by CPU during a write operations, on the data saved in cache, need to be written back to main memory or to auxiliary memory. These two popular cache write policies (schemes) are: Write-Through Write-Back
- 28. Writing Through •In a write through cache, the main memory is updated each time the CPU writes into cache.
- 29. In a write back scheme, only the cache memory is updated during a write operation. The updated locations in the cache memory are marked by a flag so that later on, when the word is removed from the cache, it is copied into the main memory.