Since Category 5e was introduced in 1999, one of the constants in structured cabling has been the 100-meter, 4-connector channel.
As data rates have increased, one of the primary differences between category systems is the frequency at which the signal is transmitted over the cable.
Category 7/7A offers a 100-meter 4-connector channel using shielded cabling, and has been designed to transmit signals at a frequency of 1000 MHz. Even though Category 7/7A operates at the higher frequency, there is no corresponding improvement in data rate over Category 6A because 10GBase-T is still the fastest twisted-pair-based data rate recognized by IEEE 802.3. Therefore, even if a Category 7/7A cabling system is installed, any available active equipment would be limited to 10-Gbit/sec performance. Category 7/7A is not a recognized category by TIA.
Category 8 is a significant departure from previous systems in that it uses a frequency of 2000 MHz, and is limited to a 30-meter 2-connector channel. Unlike Category 5e through Category 6A, which could use either unshielded twisted-pair (UTP) or shielded cable construction, Category 8 will require shielded cabling. The most likely cable construction for Category 8 will be 22-AWG S/FTP cabling.
Category 8 is also unique in that the ISO standard will recognize two different classes of product. Class I is based on the traditional RJ45 connector, while Class II will accept non-RJ45 connectors similar to Category 7/7A. While both solutions will offer backward compatibility in terms of transmitting the lower category data rates (1G or 10G), the Class I solution offers a migration path using the RJ45 connector platform. For example, a customer might install a Category 8 jack-to-jack link now, but continue to use Category 6A patch cords until the active equipment is upgraded. While the ISO standard includes both classes, the TIA Category 8 standard will only recognize a Class I solution.(from Cabling Installation & Maintenance)