What is Backward Compatibility?

R. Kayne

Backward compatibility is a feature that guarantees functionality with previous standards or versions. Backward compatibility makes it possible for technology to move ahead without making existing technology obsolete.

USB is backward compatible, so a 1.1 cable can work in a 2.0 port.
USB is backward compatible, so a 1.1 cable can work in a 2.0 port.

For example, in the fast-paced, highly competitive computer industry, manufacturers and engineers form cooperative groups to develop new standards. Once these standards are adopted, manufacturers create compatible products. This keeps the market competitive and allows consumers a broad choice of products that are guaranteed to be interoperable. If not for backward compatibility, every time a product improved, it would be incompatible with the existing infrastructure. Imagine buying a new spark plug for a three-year old car, only to find out you require a new car to use the plug!

Most devices are backward compatible, so a USB 3.0 device can be used in a USB 2.0 port.
Most devices are backward compatible, so a USB 3.0 device can be used in a USB 2.0 port.

Computer systems, software, networks, and digital devices all function with a great deal of interdependence. As each component, device, program, network, or infrastructure is improved, backward compatibility ensures the “whole” will continue to function. If other parts can only understand the language of the old standard, backward compatibility makes it possible for the new part to function using the old standard. When the system is upgraded and able to utilize the new standard, the new part uses the newer, better standard.

Backward compatibility has always been a feature of operating systems. If it weren’t, every time a consumer installed a new operating system, new software would also be required. Instead, most of our software continues to work on the new system, even though it was designed for an older operating system. It takes many years for software or a previous operating system to become legacy, giving the consumer plenty of time to upgrade.

Perhaps the first time many modern consumers became aware of backward compatibility was with the advent of the Universal Serial Bus (USB) port. This port opened the door to convenient plug and play devices, and the USB 1.1 standard was incorporated into many products. When the standard was improved to the faster 2.0, devices built to the new standard had to incorporate backward compatibility to continue to run on existing USB ports at 1.1 speeds. When the consumer updated the port to a 2.0 port, the product could run at 2.0 speeds.

Though there is no set time period, older standards eventually become legacy. In this case, current technology no longer supports them. Software designed today for Windows XP is not designed to be backward compatible to Windows 3.11, though in some cases, it is still written to be backward compatible with Windows 98.

When investing in new components, it is always a good idea to buy the newest standard available. In rare cases, a component may not be backward compatible, so if it is an issue – and it usually is – be sure to check. Backward compatibility keeps you up and running, enabling you to upgrade your system as time and the pocketbook allow.

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