Question: I run Windows on my home computer, and I noticed that my Linux dedicated server is always using a lot of RAM. Why?
Answer: Windows and Linux utilize RAM in different ways. Someone new to Linux might be alarmed to see that the amount of free RAM Linux leaves available is very small. Like Windows, Linux has virtual memory functionality, but there are two main differences:
1. Windows uses a single file, called a page file, which can grow and shrink, while Linux uses a swap partition of a fixed size.
2. Linux caches applications. For example, if Postfix, a mail server program, starts and sends some email messages, Linux will remember it even after the program shuts down. The next time it is used, it will start faster since it is cached in the memory.
Linux will keep remembering and caching applications until most of the RAM is used. Otherwise, your RAM just sits there with no purpose. But when more applications need the RAM, Linux will automatically flush the cache to make room. Therefore, if you have enough RAM, you will hardly ever need to use your swap partition.