> It is searching and writing in the background while the user or a program is doing something else. I'm not 100% sure what this is meant to mean, but if they

> It is searching and writing in the background while the user or a program is doing something else. I'm not 100% sure what this is meant to mean, but if they mean to suggest that DOS did some sort of async disk I/O, then... yeah, no, I'm pretty sure the way I recall that working is that your program did a syscall by calling an interrupt, which caused the CPU to stop running your code and start running DOS, which ran its own code (what you might today call a filesystem driver) that in turn passed execution to the BIOS (usually, at least), which ran its code to actually do the disk access, then returned execution to DOS, which returned execution to your code.