About main memory
Main memory refers to random access memory or RAM for short and read only memory or ROM for short.
RAM is where all currently running programs are stored along with any data that they're using. When a program is opened, its code is transferred from secondary storage into main memory where it can be accessed by the
processor. RAM is volatile, meaning data in RAM is lost if the power is lost.
ROM is called read only memory because you can't write over it once it is created. It is non-volatile and its purpose is to help the computer get started. It needs to load the files from your HDD/SSD with your operating
system on it. Before it can do this it needs BIOS or information about the basic input output system so it can get the data it needs. Once the operating system is running it takes over. The software that boots the computer
i.e. gets it going, is often called the bootstrap loader