This ad will deliver higher click-throughs than the same ad placed at the bottom of a page.
Some sites use frames to display advertising more prominently.
Keep in mind that most sites have repeat visitors, and most visitors view more than a single page of information, so your 100,000 impressions could actually represent 10,000 to 40,000 unique visitors. In some cases, impressions are guaranteed, in others, estimated. Some sites will charge a flat rate for estimated impressions. Most popular sites offer ad agency discounts and volume or frequency discounts. A page hit, or HTML hit, is registered every time a complete HTML page, including text and graphic files is delivered.