RAM Is Cheap So Why Don’t We Run Everything From It?

The Answer

 

There are a few reasons RAM is not used that way:

1. Common desktop (DDR3) RAM is cheap, but not quite that cheap. Especially if you want to buy relatively large DIMMs.
2. RAM loses its contents when powered off. Thus you would need to reload the content at boot time. Say you use a SSD sized RAMDISK of 100GB, that means about two minutes delay while 100GB are copied from the disk.
3. RAM uses more power (say 2–3 Watt per DIMM, about the same as an idle SSD).
4. To use so much RAM, your motherboard will need a lot of DIMM sockets and the traces to them. Usually this is limited to six or less. (More board space means more costs, thus higher prices.)
5. Lastly, you will also need RAM to run your programs in, so you will need the normal RAM size to work in (e.g. 18GiB, and enough to store the data you expect to use).

Having said that: Yes, RAM disks do exist. Even as PCI board with DIMM sockets and as appliances for very high IOps. (Mostly used in corporate databases before SSD’s became an option). These things are not cheap though.