Subject: What is bitmap(in FORTRAN & C++) and the meaning of BITMAPFILEHEADER?

Could you please tell me what the statement BITMAPFILEHEADER stands for in 
the Fortran language from the below structure:
     structure /tagBITMAPFILEHEADER/
        integer*2 bfType 
        integer*4 bfSize
        integer*2 bfReserved1
        integer*2 bfReserved2
        integer*4 bfOffBits
        end structure
From the above structure can you please tell me the meaning of bfType, 
bfSize, bfReserved1, bfReserved2 and  bfOffBits and what do they stand 
for? What is the similar structure for C++?

Another problem I would like to ask is about double precision, 
    X = DCOS(PI)
D here is a double precision. What about the below statement
    A = 0.D0   &    B = 1.D0
    PI = X * B 

What does D (in 0.D0 & 1.D0) stands for. If it is a double precision, then 
could you please explain the numerical meaning of 0.D0 and 1.D0.

Re: What is bitmap(in FORTRAN & C++) and the meaning of BITMAPFILEHEADER?