These are preventive and remedial services that physically repair or optimize hardware, including basic installation, contract maintenance and per-incident repair — both on-site and at a centralized repair depot. Hardware support also includes telephone technical troubleshooting and assistance for setup and all fee-based hardware warranty upgrades. Exclusive of parts bundled into maintenance contracts, sales of all parts used to repair high-tech equipment in carry-in, mail-in or per-incident on-site delivery models, or purchased by the internal staff to perform the repair, are included. There are four types of maintenance, namely, corrective, adaptive, perfective, and preventive. Corrective maintenance is concerned with fixing errors that are observed when the software is in use. Adaptive maintenance is concerned with the change in the software that takes place to make the software adaptable to new environment such as to run the software on a new operating system.