When DNA sequence is obtained by any experimental method, including both Sanger and next-generation methods, the data are obtained from individual template molecules as a string of nucleotide bases (represented by the letter symbols G, A, T, C). This string of letters is called a sequence read. The length of a sequence read is determined by the technology. Sanger reads are typically 500–800 bases long, Roche 454 reads 200–400 bases, and Illumina reads may be 25–200 bases (depending on the model of machine, reagent kit, and other variables). Sequence reads produced by NGS machines are often called short reads.