v$sgainfo - What means Startup overhead in Shared Pool = 496.76039886474609375

Hi

I executed this select:

select name||' = '||(bytes/1024/1024) as M from v$sgainfo;  

And the output is this:

Fixed SGA Size = 2.1639556884765625

Redo Buffers = 52.68359375

Buffer Cache Size = 12672

Shared Pool Size = 6464

Large Pool Size = 192

Java Pool Size = 448

Streams Pool Size = 512

Shared IO Pool Size = 0

Granule Size = 64

Maximum SGA Size = 30582.84765625

Startup overhead in Shared Pool = 496.76039886474609375

Free SGA Memory Available = 10240

What means Startup overhead in Shared Pool = 496.76039886474609375?

Thanks.

Regards,

Marco Cambronero Barrios