Organic SEO vs. PPC Advertising

i don't have any idea about weak nesses in Search Engine Optimization (SEO).i.e organic SEO and Search Engine Marketing (SEM).i.e. PPC advertising. SEO and SEM are two different terms but then also both have a direct effect on each other. Search Engine Optimization is what is done to our site to ensure that the end users have a friendly easy to use web site with the help of SE like Google, Yahoo, MSN Ask,etc.and those SE crawl go through your site content. Search Engine Marketing is doing the advertising and marketing of our site. Basically SEM is done "offsite" and SEO is mostly done "onsite". SEO is more inclined towards technical process than SEM .
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