Subtitles of the Movie

One of the um, additions to the processor that really made higher speeds happen was the cache. And I want to talk just a second here about the processor cache. The processor cache is really just a waiting room for commands that are headed to the CPU. As the ah processor manufacturers began to try to push the speeds up on the CPU they found that a, a couple of things were hindering them. And I want to kind of draw you a little diagram here, and show you. I want you to think about ah, there's four basic tasks that have to be carried out on, on, on every task that gets sent in to the processor. And the problem is that when you send these tasks in, okay, this one can be completed, this one can be completed, but this one's going to take a while, and this one can be completed. So this entire process had to sit still until this one could be completed. Okay, so you would go through a number of clock cycles, and this slowed things down. And also, in the meantime, you might have other commands or, or other tasks backed up back here, waiting for this one to ah, to be carried out, right. And so what they did was with the processor cache, they did all kinds of cool things. Number one they would, they would put these things in cache very fast because, number one the processor's the fastest running piece of hardware on the machine. It's running faster than the RAM, it's running faster than the clock because the system clock is pulsing, but the processor's adding a multiplier to it. So, again, like I was, ah I mentioned in another video, it's almost like a, a drummer playing thirty-second notes to everybody else's whole notes, and so, or quarter notes, and so it allowed pipelining to be used, and so what's basically what's happening they just stack the commands up in this cache and it would actually rearrange those. And so, if it saw one that was going to be pretty complex and take a while, it would submit it, but it would get the other ones in order. So it actually ran some of the commands out of order because they were quick tasks and they could be taken care of and so forth, and so it basically allowed a lot more complex and more efficient use of clock cycles. Basically I said, You know what, if there's going to be a tick, we want to make sure that we're passing as much work into and out of the CPU as we possibly can. And this was the key to many of the CPU improvements. Now what's been interesting through the years is what's happened to these processor caches. The first one we saw was an L1 cache, and this was an S-RAM memory chip located inside the CPU. Now, it wasn't really part of the CPU per se, it wasn't an internal part, it was just simply located inside the CPU, it was, it was on the same board as the CPU if, if you will. And this thing's job was to simply hold data. It was the first place that the CPU put it and it's the first place the CPU looks for the data. Now, interestingly what they found out was, is that making this cache larger didn't make it more efficient, it actually made it less efficiently, because it was harder to look through the data and, and keep up with it, and so, they went to an L2 cache, and this cache was located on the motherboard, and so what would happen is, is the CPU would look here second for data and they found that having small amounts of data in two places was more efficient than a large amount in one place. Now what's, something that most people have never heard about, and is really interesting, is there is also an L3 cache, or level 3 cache, and this is found on high-end specialized CPUs and most techs never see these things. But when you're talking about really high end servers that are doing you know massive heavy lifting, you, these, these guys will also have an L3 cache. Now down through the years these caches have gotten larger and they've gotten fancier, but the bottom line, they're still doing the same thing. They're simply parking information. It's almost like a staging area where the commands for the processor go into these caches and then there's a little manager inside there that's reorganizing these things, it's getting them in line, you know single file, tight line, no spaces, you know, suck in that gut, all that kind of stuff. And then they're running these, these commands through in the most efficient ah, fast as possible way. So, on the exam just remember the L1 cache is on the CPU and it's going to check it first, the numbers give it away. The level two cache, or L2, is the next one that checks, and then L3 is on the high end PCs and you'll never see that in a normal ah desktop workstation type computer.