The browser executes a system call to request the file-save operation. This triggers a hardware interrupt, causing a transition from user mode to kernel mode. The kernel performs the file-write operation, and then returns control to the user program, switching back to user mode.

The browser directly accesses the hard drive to save the file. There is no need to switch to the kernel mode because all operations are handled by the program itself.

The browser saves the file to a temporary location in its own memory space. The kernel periodically scans all user programs' memory and automatically saves any new files it finds to the hard drive in a background process.

The user program sends a message to the kernel. The kernel then switches to a separate "device mode" to communicate with the hard drive. After the operation is complete, the kernel switches back to user mode and notifies the user program.