**Some true false question ,please try to solve**

1.The operating system is the first layer of software closest to the bare machine(T/F)

2.The PCB is the indicator of whether a process exists or not(T/F)

3.The "DMA" method does not require CPU intervention in the data transfer process, but after the data transfer, it still needs to send interrupt to CPU for handling data verification.(T/F)

4.In the "P" primitive, after the operation semaphore minus 1. If the value of semaphore is greater than 0, it returns directly. If the value less than or equal to 0, the calling process enters the waiting queue.(T/F)

5.In paging system, the size of a page can vary depending on the requirements of each process.(T/F)