A web page can contain text, image files, multimedia clips and so on. When the size of all these elements present on a web page is added you get the total number of kilobytes a visitor will have to download to open that particular page of your website. Simply, it is known as page size.
If a person has to wait for more than 10 seconds to download your page then chances are that he/she will move on to the next option he/she has. Though high speed Internet is gaining popularity steadily, yet there are many users who still use orthodox 56-k dial up modems. Thus, it is advisable that you keep your web page under 60 K in size to make it downloadable by maximum number of visitors.
Again, there are many people around the world who still use the old 800 x 600 resolution and you will amazed to know that they comprise around 40% of the net surfers! Thus, even if you have a high-resolution setup, you should still try to design your pages according to 800 x 600 resolution. Otherwise, the visitor will have to scroll though your page horizontally, which can be very frustrating.