1000BASE-X is a group of standards for Ethernet physical layer standards, specified within the IEEE 802.3.z standard.It is used for gigabit Ethernet connections that transmit data mainly over fiber optic cable, and sometimes over copper-shielded cable.

The range of 1000BASE-X starts at 25 meters for copper and can be extended to 70 km with a single-mode fiber channel. All of these standards use an 8b/10b encoding scheme, in which 8 bits are used for data transmission and 2 for error correction.

The first letter tells us which kind of wire we are talking about: 

“T” means twisted-pair cable (e.g. the common Cat5 in use today)

“K” means a copper backplane

“C” means balanced copper cable

“F” means optical cable

“B” uses two wavelengths over a single optical cable

“S” means short-range multi-mode optical cable (less than 100 m)

“L” means long-range single- or multi-mode optical cable (100 m to 10 km)

“E” means extended-range optical cable (10 km to 40 km)

“Z” means long-range single-mode cable at a higher wavelength

Next is the coding scheme for data on the wire 

“X” means 4B/5B block coding for Fast Ethernet or 8B/10B block coding for Gigabit Ethernet

“R” means 64B/66B block coding

Finally, we have a number representing the number of parallel “lanes” for data 

“1” would mean serial (non-parallel) but is omitted instead

“4” or “10” are available for copper wire

Just about any other number could be used for optical lanes or wavelengths

Ethernet was the result of the research done at Xerox PARC in the early 1970s. Ethernet later evolved into a widely implemented physical and link layer protocol. Fast Ethernet increased speed from 10 to 100 megabits per second (Mbit/s). Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. The initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE 802.3z, and required optical fiber. 802.3z is commonly referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or (non-standard) -ZX. IEEE 802.3ab, ratified in 1999, defines Gigabit Ethernet transmission over unshielded twisted pair (UTP) cabling, and became known as 1000BASE-T. With the ratification of 802.3ab, Gigabit Ethernet became a desktop technology as organizations could use their existing copper cabling infrastructure.IEEE 802.3ah, ratified in 2004 added two more gigabit fiber standards, 1000BASE-LX10 (which was already widely implemented as vendor specific extension) and 1000BASE-BX10. This was part of a larger group of protocols known as Ethernet in the First Mile.Initially, Gigabit Ethernet was deployed in high-capacity backbone network links (for instance, on a high-capacity campus network). In 2000, Apple's Power Mac G4 and PowerBook G4 were the first mass-produced personal computers featuring the 1000BASE-T connection. It quickly became a built-in feature in many other computers.

There are five physical layer standards for Gigabit Ethernet using optical fiber (1000BASE-X), twisted pair cable (1000BASE-T), or shielded balanced copper cable (1000BASE-CX).