It has been noted in the industry that Dell could advertise itself more. However, there is a clear marketing strategy covering the four crucial Ps. Dell uses TV, print media, online ads and distributes brochures through newspapers, e.g.
Star In-Tech in Malaysia, a popular issue of IT consumers and tech enthusiasts. It also gives online promotions through contests and sends user newsletters providing latest information to increase customers' interest.
Dell isn't one to advertise much but when they do, they go all out. They spent 3.5 million on Spider Man ads and there were only a couple of them. But for the most part, they rely on word of mouth. Some say that they don't need to spend their money advertising but should spend advertising money on making better products. Others think their products are so good, they don't need to advertise.
Why Dell doesn't advertise has never been really been said, just speculated on. Perhaps they don't feel they need to but the company sure has had some lean times that extra sales could have possibly solved. All in all though, everyone does seem to know who they are across the entire world and people already have formed an opinion, good or bad, so advertising might be pointless.