What means for 'memory used' in sp_configure output?

I use sp_configure 'max memory' and got the result:

1> sp_configure 'max memory'

2> go

Parameter Name                 Default     Memory Used Config Value

         Run Value   Unit                 Type

------------------------------ ----------- ----------- ------------

         ----------- -------------------- ----------

max memory                           45056     8000000     4000000

             4000000 memory pages(2k)     dynamic

(1 row affected)

(return status = 0)

the max memory is configured as 4000000( roughly 7.6G). but there is one 'Memory Used' is 8000000. what' it? it is double of 'max memory' value and run value.  it's 15G memory used?