Why do CPUs Need Caches? - Computerphile

We've all heard of web browser caches, but why does a super fast modern CPU need a cache? Because it's too fast. Dr Steve "Heartbleed" Bagley explains.

This video was filmed and edited by Sean Riley.

[UltimatePerfection]

Why RAM access is so slow? Because it has to take a bus.

[Небовглазах-ны]

2:42 all my years-long confusion about cache wiped out with the 20 second animation. It's fantastic Computerphile!

[TheEulerID]

The cache is the kitchen cupboard, main memory is the corner shop and disk storage is buying on-line at a supermarket. It's a lot quicker to get the cornflakes out of the cupboard than walk to the corner shop for the same item, let along wait a couple of days for them to be delivered.

[robharwood]

Good use of animations to help visualize the explanations. Kudos to the animator(s).

[Tata-Jooma]

4:58 "You only need a relatively small amount of cash to make a significant difference". #gangsta #hollahollagetdolla

[DrRChandra]

cache hits and misses, cache consistency, cache locality, write-through vs. writeback, cache segmentation (as mentioned, instruction and data), multiple cache levels...cache is a moderatly complex and very much researched topic. This however is a great introduction to the basics.

[simonh]

Modern CPUs often have three caches, the one that is described by this video (separate for data and instructions) is the L1 cache, the fastest, and every core has it's own. L2 is larger often shared between cores (2 on my system) . L3 is the biggest and there is only one for the actual chip on which the cores are.

[jaffarbh]

Just a bit of clarification, nowadays RAM chips can be clocked faster than the CPU, but the latency remains quite high (relatively), so cach memory is here to stay indeed.

[Neeboopsh]

That cpu at 3:09 is rocking a bernie sanders look.

[DavidTurnell]

Thank you so much for not saying uuum, uuum, uuum every sentence. Remember you are the result of tens of thousands of years of recent human evolution. Be proud of this.

[davidratkay]

Glad there is a computer channel like this.

[vladislavkaras]

Really great explanation. Simple and informative!
Though, it is kinda sad, that it is impossible to disable cache, just to feel, how important it is.

[pacrat]

Always so excited to open my browser on a new computerphile video! Thanks for the quality videos.

[jsbarretto]

Can I just say now how much I appreciate you putting the DuckDuckGo logo into this video... Well done. Best search engine there is by miles.

[VickyBro]

Wow. What a clear and succinct information.

[SCB]

Best explanation about what cache is I've ever listened to.

[knaik]

Is there any major difference between the different types of Caches? I have heard of terms L1, L2, and L3, but I'm not sure what the differences between them are significant.

[ericsbuds]

I like Dr Bagley's explanations. He is great. Thanks for the interesting vid! love learning the innerworkings of computers!

[Majornerdacc]

This is the best channel in the world.

[whuzzzup]

You could have elaborated on what's going on with L1-L3 Caches. Is one for data the other for instructions, or do they have no preferences? If they can/will store the same, how does the CPU decide what to put where as they have different speeds?
I think this should be even in a beginner video, because you will be confronted with those values in most ads.