No, I was talking about caching disk reads in ram. Nearly all modern operating systems do this. If you have enough ram, the data you read from disk is cached in ram. With spinning disk, especially shared 7200rpm spinning disk, for interactive use? generally speaking, you have human-noticeable latency every time you do a blocking read that isn't cached.

Because of this, having enough ram to cache all the data you read often is extremely important to system performance when you are on spinning disk. (and having a pagecache that doesn't dump all the stuff you use often when you do a one-time read of a big file.)

I was suggesting that SSD might have fast enough read-access that for some applications, the penalty for reading from ssd rather than from pagecache might be small enough to not be a big deal, meaning you could get acceptable performance out of a system with less total ram.