False-colour scanning electron micrograph of part of a 256-kilobyte (DRAM) Dynamic Random Access Memory integrated circuit, or silicon chip. The colours distinguish the layers of electronic pathways which cover the surface of the chip. The half-sunken pad on each light blue pathway is a single transistor memory cell. Each DRAM will have 2-4 million such transistors. DRAMs do not store information on a permanent basis; instead their memory cells are refreshed every 2 milliseconds. A mainframe computer may contain 400-1000 DRAMs. The orange particles at far right are contaminants. Magnification: x1300 at 35mm size, x3100 at 6x6cm size.