If access is made to the inputs and outputs via the operands "I" or "Q" in the user program, then there is no direct access to the input/output modules. In this case, access is made to a memory area in the CPU's system memory. This area is called the process image of the inputs (PII) and the process image of the outputs (PIQ). The contents of the process image (PII and PIQ) do not reflect the actual values of the inputs/outputs, but the values at the time the process image was updated. If more recent values are required for individual processes, you also have the option of direct peripheral addressing. You would only want to grab the live value from the PIW table in cases where the PLC scan time is long or the value is changing very rapidly and some action has to be taken before the next scan.
WORD and DWORD are both unsigned integer types.
Global Input is used to described a Global Memory item that is being used as an input to a Function or Function Block and is not a different type of memory.