These days you can get servers with Terabytes of RAM, so a lot of people (most?) could fit their data in memory. I just took a gander to HPE's website and you

These days you can get servers with Terabytes of RAM, so a lot of people (most?) could fit their data in memory. I just took a gander to HPE's website and you can get proliant servers with up to 12 TB of RAM (you might be able to get them with more RAM, did not check in detail)