When I was studying (late 00s) I worked at a large supermarket chain in the UK that had this. The system was surprisingly well designed. It was based on Window

When I was studying (late 00s) I worked at a large supermarket chain in the UK that had this. The system was surprisingly well designed. It was based on Windows NT (somehow hardened, as I never saw a checkout show a BSOD or fail to boot) and was designed before a time when you had a continuous internet connection. There was a mini-server in the back office, and every night it would sync with HQ. This meant all functionality, including taking credit card payments and loyalty, could be done offline. One time we had a electrical systems failure in the store, and everything - including chillers - went down. However each checkout had its own UPS and continued to operate without issue.