Fuctions reserved_pages and curunreservedpgs

Dear Colleagues,

Should these queries fetch me same results for the Data used??? I do not get , Could you pleas help me here, if I am wrong? and give me more insight?

Using reserved_pages: ( I get 186388.6 MB)

select @DataPagesUsed = sum(convert(numeric(19,5), reserved_pages(4, id))) from SID..sysobjects

Using curunreservedpgs : ( I get 187678 MB)

select "DataUsed(MB)"= str((datasize - dataunreservedpgs) / @numpgsmb, 9)

where the values are taken as follows-----

(

select "dataunreservedpgs" = sum(curunreservedpgs(4, lstart, unreservedpgs)) from master.dbo.sysusages where dbid =4 and segmap !=4

select "datasize" = sum( size ) from master.dbo.sysusages where dbid =4 and where dbid =4 and segmap !=4

select @numpgsmb = (1048576.0 / v.low) from master.dbo.spt_values v where v.number = 1 and v.type = "E"

)

and finally reserved_pages takes lots of time than compared to curunreservedpgs  to provide the output.

P.S : The database is used has a dbid = 4

Kind Regards,

Ajith Prabhakaran