UPDATE

I am using PG on windows for development. While testing some queries I found that updates are much slower as compared to other database systems. (On avarage MySQL updates 4-5 times faster than PG in a single unique index on primary key) Why?
Another thing that I noticed is when any single column in a table is updated and having no index many (in my case 7) indexes on different columns, It takes about 180-200 secs. But when any single column in a table is updated and having many (in my case 7) indexes on different columns, but does not have index on the column that is being updated, It takes about 800-900 secs. Why?
What can be done for such updates to make them faster?
Thanks
CPKulkarni