from the svrmgr prompt
svrmgr>show sga
it shows
Total system global area: 715053084
fixed size: 75804
variable size: 244789248
Database buffer: 459694080
Redo Buffers: 10493952

I want to decrease my SgA size:

sga size should not be greater than 2/3 of physical memory. my server windows Nt meory is 1 GB.
what includes fixed size,vraibale size. and database buffer size. my database buffer size is also high.

pls tell me how to find each and every thing for sga details.