Cache what is block size

Email Required, but never shown. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. Now live: A fully responsive profile. Related 1. Hot Network Questions. Question feed. Accept all cookies Customize settings. Then the tag is all the bits that are left, as you have indicated.

Asked by: I? In the example the cache block size is 32 bytes , i. How many bits is a word? How is a block found in a cache?

When the CPU tries to read from memory, the address will be sent to a cache controller. What are cache misses? Cache miss is a state where the data requested for processing by a component or application is not found in the cache memory. It causes execution delays by requiring the program or application to fetch the data from other cache levels or the main memory. What is miss penalty? The fraction or percentage of accesses that result in a miss is called the miss rate.

The difference between lower level access time and cache access time is called the miss penalty. What happens when a private and shared items are cached? Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Concept of "block size" in a cache Ask Question. Asked 10 years ago. Active 1 year, 9 months ago. Viewed 47k times. Improve this question. Add a comment. Active Oldest Votes. Let's say you want a 1-MiB 2 20 bytes cache.

What do you do? You have 2 restrictions you need to meet: Caching should be as uniform as possible across all addresses. How do you do this? Use remainder! With mod, you can evenly distribute any integer over whatever range you want. You want to help minimize bookkeeping costs.

That means e. How do you do that? You store blocks that are bigger than just 1 byte. You now have a few options: You can design the cache so that data from any memory block could be stored in any of the cache blocks. This would be called a fully-associative cache. The benefit is that it's the "fairest" kind of cache: all blocks are treated completely equally.

So a larger block size means we'll be using the SRAM more efficiently. Since there are 16 bytes of data in each cache line, there are now 4 offset bits. The cache uses the high-order two bits of the offset to select which of the 4 words to return to the CPU on a cache hit.

There are 4 cache lines, so we'll need two cache line index bits from the incoming address. And, finally, the remaining 26 address bits are used as the tag field.

Note that there's only a single valid bit for each cache line, so either the entire 4-word block is present in the cache or it's not. Would it be worth the extra complication to support caching partial blocks? Locality tells us that we'll probably want those other words in the near future, so having them in the cache will likely improve the hit ratio. What's the tradeoff between block size and performance?

We've argued that increasing the block size from 1 was a good idea. Is there a limit to how large blocks should be? Let's look at the costs and benefits of an increased block size.

With a larger block size we have to fetch more words on a cache miss and the miss penalty grows linearly with increasing block size. Note that since the access time for the first word from DRAM is quite high, the increased miss penalty isn't as painful as it might be.