1U is equal to 1.75". Rack mounted servers are measured in U (stands for unit) and therefore most colo providers measure colocation space in a U.
Colocation means you send your server to a professional (hopefully) data center to host. This provides you with redundant power backed up by UPS and generator and a connection to the Internet. Different providers handle the connection differently. Usually the data centers don't sell less than a cabinet or half cabinet. Some sell bandwidth, some just provide a connection to the providers cabinet or router.
Do your homework before choosing a provider. Pay attention to several things...
1. Quality of the data center. Some are definately better than others.
2. If you need a small amount of bandwidth, go with a provider who offers such connections.
3. Do they provide support? If so, how do they charge for the support?
4. Who are their bandwidth providers? Again, some are much better than others.
5. Do they offer a SLA? (Service Level Agreement) (Typically a guarantee of minimum service)
Price is always important but shouldn't be the only criteria. Once you determine your needs, you can then pick the provider who fits your needs the best.
Colocation isn't always expensive (guess that really depends upon your definition of expensive). The reason for the cost is data centers are very expensive to build and maintain.
Brad @ Xiolink
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