Data can be transferred in parallel or serial data streams. For example, Advanced Technology Attachment( ATA) transfers data in parallel, while Small ComputerSystem Interface( SCSI) transfers data in serial.
Serializers/deserializers (SerDes) are used to convert a parallel data stream into a serial data stream and vice versa. Serializers/deserializers are units consisting of a serializer and a deserializer. While the serializer turns a parallel 8-bit data stream into a serial one, the deserializer turns a serial bit data stream into a parallel one. By adding the clock, the parallel 8-bit data stream becomes a serial 10-bit data stream via 8B/10B encoding.
In terms of structure, the serializer of a serializer/deserializer consists of a shift register, First In First Out( FIFO), an encoder for 8B/10B coding. The deserializer consists of the serial receiving device, the 8B/10B decoding and the transmitting side shift register.
By converting the parallel transmission to a serial transmission, synchronism problems that occur with parallel transmission are eliminated. Another important aspect is the reduced number of data paths and connection points. Therefore, SerDes are used in Gigabit Ethernet and in GbE systems with higher data rates of 25 Gbit/s and 50 Gbit/s.