lec4 -L1 and L2 cache

L1 and L2 cache
Cache memory, in its various forms, plays a particularly important role in a processor’s performance. Cache can improve a processor’s efficiency by offering it access to the data it needs more quickly than regular memory would. Not only are cache memory chips (typically Static Random Access Memory, or SRAM) faster than regular memory chips, but they also have a faster connection to the processor.
The way cache works

Because of the way most software works, processors tend to spend a lot of their time either performing the same operations over and over or performing several different operations on the same set of data. Well, one day, somebody realized that if a processor could access used instructions and data more quickly, it could run much more efficiently. So, a clever designer came up with the idea to create a special "work area" right alongside the processor, called a cache, that temporarily stores the data and instructions the processor used most recently. The idea was (and is) that once the processor finishes what it is working on, it can "fetch" what it needs next from this nearby area instead of getting it from regular memory, which is further away and takes longer to get to.
Processors aren’t the only computer-related component to use a cache. Many software programs, such as Web browsers, also use a cache. While a processor’s cache and a browser’s cache are not the same thing, they are conceptually similar. For both components, a cache speeds up access to recently used information.
Web browsers, for example, set up memory and/or disk caches (which use RAM or space on the hard disk, respectively) to store recently used files. The thinking is that you probably will want to use the files you’ve accessed recently again. If they’re stored either in RAM, or on disk, the browser will be able to get to them much more quickly than if it had to go out to the Internet again. For example, when you hit the Back button on your browser, the Web page loads almost instantly because the files the browser needs are nearby. If there wasn’t a cache (or if you empty or clear the files in the cache), going back to the previous page would take just as long as when you called it up in the first place. This is similar to what happens with processors and their specialized cache; if the information the processor needs is close by in the cache, the processor operates quickly without waiting, but if the information isn’t close by, the processor has it to request it from main memory. (The main memory isn’t as slow as the Internet, of course, but it is a lot slower than getting it from the cache.)