One reason is the number of CPU cycles per second is INCREASING and the cost of processors is DECREASING. For managing the data in memory, there is five-minute rule which is based on the suggestion that it costs more to WAIT for the data to be fetched from disk than it costs to keep data in memory so it depends on how often you fetch the data.

For example: there is a table and no matter how large it is and this table is touched by a query at least once every 55 minutes, it is less expensive (in hardware costs) to keep it in memory than to READ it from memory and if it is frequently accessed it is less expensive to store it in memory.

One reason is the number of CPU cycles per second is increasing and the cost of processors is decreasing. For managing the data in memory, there is five-minute rule which is based on the suggestion that it costs more to wait for the data to be fetched from disk than it costs to keep data in memory so it depends on how often you fetch the data.

For example: there is a table and no matter how large it is and this table is touched by a query at least once every 55 minutes, it is less expensive (in hardware costs) to keep it in memory than to read it from memory and if it is frequently accessed it is less expensive to store it in memory.