What is co-location?
Co-location refers to the way IT equipment and resources are located or installed. This usually refers to the network hardware resources owned by an organization, such as web or database servers, that reside outside the organization's environment and are 'shared' with the hardware of another organization, usually an ISP or service provider. This is usually because the ISP might be the best candidate for web server hardware maintenance for the organization and it would be better to keep the hardware in a more convenient location as ISPs have specially built locations for network hardware.
Co-location facilities are commonly used by service providers for the storage of equipment used by their customers and, of course, their own. These facilities provide power, cooling, space, and physical security for the equipment. The reason organizations jointly locate their hardware resources is because they are unable to provide an appropriate location and maintenance for such specialized hardware on their premises.
It would be too expensive for them to create specialized facilities while the service providers already have these types of facilities due to the nature of their business.