Before USB, what serial connector type was commonly used for communication, keyboards, mouse, or game controllers?

DB9 was the "D" format, a 9-pin serial connector type for keyboards, mice, and other portable peripherals. It was also used to communicate between a computer and some controlled switches. Small Computer Systems Interface (SCSI) is a drive connector and technology that allows up to 15 drives to be daisy-chained together. The PS/2 connector, commonly known as a mini-DIN, is newer than the DB9 connector but older than the USB connector. It has 6 pins and was used to connect mice (green color-coded) and keyboards (color-coded purple). Apple devices use Lightning ports.