A) The main task of port device management is to complete the I/O requests made by users and classify I/O devices for users. and B) Whenever a process makes an I/O request to the system, as long as it is secure, the device allocator will assign the device to the process according to a certain policy. and C) Device management can virtualize a physical device into multiple logical devices through virtualization technology, providing multiple user processes to use. and D) In order to alleviate the problem of speed mismatch between CPU and I/O devices and improve the parallelism of CPU and I/O devices, in modern operating systems, almost all I/O devices are exchanging numbers with processors Buffers are used at all times.