We obtained our first Illumina GAII Next Generation Sequencer already in 2008 and upgraded via the HiSeq2000 to the HiSeq2500 in 2013.
Surface bound, clonally amplified short DNA fragments are sequenced in cycles by a synthesis process in which a blocked fluorescent base is incorporated and then imaged. After the block is removed the next base can be incorporated and a new cycle starts. The images are analyzed and the colored spots are translated into a base sequence. The maximum length is 300 nucleotides per single read.