Let's look at some specs, do some math, and make an analogy to help us relate!
First, let's compare the retrieval time from different media types:
- RAM: 3 nanoseconds
- Mobile Disk = 12 milliseconds = 12,000,000 ns
- Standard Disk - 9 milliseconds = 9,000,000 ns
- Server Class HDD = 3 milliseconds = 3,000,000 ns
- Server Class SSD = 0.1 milliseconds = 100,000 ns
When we compare these media, we see that RAM is at least a 1 million (and likely 4 million) times faster than HDD and 33,333 times faster than SSD. But how do you even conceive what those kinds of numbers mean?
Let's play a game where nanoseconds become regular seconds just to get an idea of comparative speeds.
Imagine you are at a restaurant, and you ask the server for some ketchup (or catsup if you prefer) for your meal. The server looks at the adjacent empty table, grabs the available bottle of ketchup, and hands it to you at RAM speed: total time = 3 seconds.
Now if your server was operating like a standard High Speed Server HDD, it would take them... 3,000,000 seconds = 34.7 days = over a MONTH to get you the ketchup!
Heaven forbid your sever is using a Standard HDD because that would be 9,000,000 seconds = 104 days = 3.4 months!
And if your server is grabbing your "ketchup" from a Mobile HDD, it would be even worse: 12,000,000 seconds = 139 days = 4.6 months!
Even optimized with a Server class SSD your server is probably going to be slower than you would want to wait: 100,000 seconds = 1.15 days.
Hopefully the lesson is not lost on all of you:
Cache is KING!
Invest in your RAM - and look for options in your software to optimizes RAM and cache usage!
That is all.