AMD were once one of the few known CPU manufacturers back in the 1990's when the K6 series of processors saw the light of day; this era saw their development teams simply not being able to keep up with the might of Intel. Not only did Intel have a larger R&D team, but also a much larger capital to put into marketing and advertising as well as striking deals with companies to use their own technologies; all of these things enabled Intel to stay in front. It wasn't until AMD acquired some licensing agreements that it was able to start using some of the Intel Multimedia Extensions that managed to help accelerate 3D rendering on the early 3D graphics cards.
It wasn't till AMD brought forth its K7 architecture that it became a real threat, and AMD was hammered by Intel in the beginning for it too. Companies were put on notice that if they went ahead and supported AMD by producing boards compatible with their original Slot A designs, they could expect to pay a price premium on the now failed i820 chipset. When Intel dropped the ball with the i820, companies soon dropped the Intel threats and started to mass produce boards for AMD Athlon processors, thus began the CPU war, which AMD managed to win. Athlon's architecture managed to simply kill the Pentium III processor at a clock for clock speed, and it was also capable of beating Intel to the 1GHz CPU barrier by three days, a definite milestone.
When Pentium 4 was first introduced, big things were expected from it. However, sadly Intel again dropped the ball. The Netburst architecture while able to give clock speeds well ahead of anything AMD was able to produce at the time, it simply couldn't outperform the K7 architecture that matured onto the Socket A market and increased by adding in some of Intel's own SSE instruction sets, making it a much more efficient processor.
When K8 made its appearance, Intel was simply spinning their wheels in the mud. K8's integrated memory controller and its highly efficient SOI production process managed to outperform any Intel CPU, including the dual core HT Extreme Edition CPUs Intel released (also known as heaters due to their 130watt TDPs). It seemed as if AMD couldn't be beat.
However, Core 2 managed to show up and quickly turn things around. From here on, AMD went downhill very quickly. AMD's aging K8 architecture couldn't keep up with the performance on a clock for clock basis with the Core 2 series, and the new TDP's from Intel's Core 2 managed to knock AMD off the top rung.
It has since taken some time for AMD to come up with a new addition to its CPU portfolio. Already attempted once, AMD had to re-design some of the CPU's due to a hardware problem that results in errors if the additional cache memory is used; today AMD has corrected this and released what is now known as the "B3" stepping revision of its Phenom Processors, the first series of CPUs to support the K10 architecture.