the Calculation about periodic system

[lifj]

Hi, Every body!

         I am a new user of cp2k. I have to ask a very superficial
question, because, I found  that I can not figure out it by myself,
finally.
         Please look at the cell section of the input file for a
periodic system:


 
&CELL
            #Mg & P6_3/mmc-D_{6h}^4 #194 & hP2 & A3 & Ashcroft and
Mermin, 77
           UNIT
SCALED_ANGSTROM
           A   1.60500000 -2.77994155
0.00000000
           B   1.60500000  2.77994155
0.00000000
           C   0.00000000  0.00000000
5.21000000
         &END
CELL
 
&COORD
           Mg  0.33333333  0.66666667  0.25000000     1.60500000
0.92664718  1.30250000
           Mg  0.66666667  0.33333333  0.75000000     1.60500000
-0.92664718  3.90750000
         &END
COORD

       Why are there six colums in &COORD section, and what does every
column means? Any words for me will be helpful. Looking forward for
your reply!

        Thank you for your time!