𝗧𝗛𝗘 𝗖𝗢𝗡𝗡𝗘𝗖𝗧𝗜𝗢𝗡 𝗕𝗘𝗧𝗪𝗘𝗘𝗡 𝗨𝗦𝗘𝗥 𝗣𝗥𝗢𝗚𝗥𝗔𝗠𝗦 𝗔𝗡𝗗 𝗢𝗦 𝗞𝗘𝗥𝗡𝗘𝗟

The relation between the user mode and the OS kernel is a heavily guarded process. User mode is basically where the user program runs and does the basic things with limited privileges and kernel mode is unrestricted access to the whole system and hardware. By default, user programs can’t enter kernel mode to ensure the safety of the system. 𝗦𝗬𝗦𝗧𝗘𝗠 𝗖𝗔𝗟𝗟 - 𝗧𝗛𝗘 𝗕𝗥𝗜𝗗𝗚𝗘 As user programs are not directly given access to the Kernel. There is a bridge that is called sytem call where the OS is the guard who decides who gets to enter and where to go inside the kernel. System call is just an abstract concept, behind the scene this is just a instruction called “Trap” (syscall). 𝗧𝗥𝗔𝗣 𝗟𝗜𝗙𝗘 𝗖𝗬𝗖𝗟𝗘: 𝗧𝗛𝗘 𝗥𝗘𝗤𝗨𝗘𝗦𝗧: If a program wants to do something it does not have the privilege. It calls a standard library function to make this request. 𝗧𝗛𝗘 𝗧𝗥𝗔𝗣: Inside the library function, there is a machine instruction called trap or syscall. Which is executed. 𝗦𝗔𝗩�