Legacy operating system loader is a term used to describe a program that loads an older operating system on a newer computer. There are several synonyms for this term, including boot loader, system loader, and startup loader. A boot loader is responsible for loading the operating system into memory and executing it, while a system loader is a program that loads the operating system kernel into memory. A startup loader is used to load and run applications when a computer is booted up. These synonyms are often used interchangeably in computer terminology and may refer to different types of loaders depending on the context.