Written by software development companies,canned software is sold on the open market to a broad range of users with similar requirements. Some companies combine software and hardware and sell them as a package. These are called turnkey systems, because the vendor installs the entire system and the user needs only to "turn the key." Many turnkey systems are written by vendors who specialize in a particular industry. For example, specific systems are geared toward doctors and dentists, automobile repair and service companies, full-service restaurants, fast-food outles, video rental businesses,and other retail stores.
A major problem with canned software is that it often does not meet all of a company's information of data processing needs. This disadvantage can often be overcome by modifying canned software. Generally, the best way to accomplish this is to have the software vendor,rather than the in-house programming staff, make the modifications. Modifications the are unauthorized by the vendor may not be supported and may make the program unreliable and unstable. Some companies have used this approach quite successfully. For examples, about 90% of Dow Chemical's softwareconsists of canned packages that have been modifies to match its business processes. The rest is custom software written in-house.