To maintain optimal performance, one typical recommendation suggests that when the memory usage associated with a particular cpu-based system averages % or more over prolonged periods, you should consider adding more memory.

60

Explanation:

One of the most important part of the computer is the memory. Computer memory generally refers to the RAM, ROM and Cache. The CPU depends entirely on the memory for access to instructions and data, as this must first be loaded into the memory before the CPU can use. The RAM is that temporary memory that holds operational data and running applications and sits in-between the hard disk and the CPU. The implication of this is that for a PC to maintain stable operation, it requires sufficient memory space for usage, and when memory usage goes beyond over 60% over an extended period of time, the PC's performance will be affected leading to freezing as a first symptom.