These terms are the certain condition that must be considered when buying a broadband :
- Availability
- Speed, performance, and your browsing habits
- Bandwidth, Download Limits, and Fair Usage Policies
Availability
The first thing you should do before searching for a broadband package is perform a local availability test  to see whose services you can sign up for, as there's little point in  comparing prices and services of all the available packages if you can't  actually receive all of them.
The majority of broadband  connections in the UK are made through copper wire phone lines, and so  the availability of an ISP's broadband services will depend on if they  have installed their equipment in your local telephone exchange.  Broadband services provided over a phoneline are generally referred to  as ADSL (Asymmetric Digital Subscriber Line) services. The service is  'asymmetric' because the achievable download speeds over the phoneline  are generally faster than the upload speeds; most home internet users  download rather than upload files, which is why ADSL is marketed towards  home customers.
Most other broadband services are delivered to  households through a fibre optic cable line - again, availability will  depend on if you live in an area where a cable network has been  installed.
You can perform an availability test  by typing your postcode into the appropriate window on our main page,  which will then provide you with a list of the ISPs who are operating in  your postcode area.
Speed, performance, and your browsing habits
Once  you know which services are available in your area, you should then  consider what you use the internet for, and how important a fast  connection is. Ideally, you will want the fastest connection possible,  regardless of your browsing habits, but a fast connection speed is  especially important if you intend on playing either PC or console games  online, or downloading music and movies.
Broadband speeds are measured in 
Mbps,  a rate of data transfer equal to how many megabits per second can be  transferred to your computer from a website or another user's computer -  for example, a three and a half minute long music file in MP3 format is  roughly equivalent to 3MB, therefore you would in theory be able to  download one song every 4 seconds if you had a connection speed of 6Mbps  or above.
ADSL and Cable
Several factors affect the  performance and speed of your connection. A good rule of thumb for  calculating your connection speed if you are signing up for ADSL  broadband is to find out how far away from the nearest telephone  exchange your house is - the closer you are to the exchange, the faster  the speed will be.
Cable broadband networks are not affected by  proximity to an exchange in this way: cable connection speeds are more  dependent with the amount of user traffic in your local area, so if you  live in a street where several people are accessing the internet via  cable, then your net performance can be affected by this.
Bandwidth, Download Limits, and Fair Usage Policies
Bandwidth  is a term used to apply to may things, usually to measure the capacity  of a communications channel - in relation to broadband services, the  'channel' will either be an ADSL or cable phoneline. The majority of  broadband packages will have a set monthly limit on how much bandwidth  you can use, usually measured in gigabytes (
GB).
The  monthly limit, often called a download cap or usage limit, reflects how  much information you can download in one month, including music and  video files, updates and new patches for your programs. Using the above  example, downloading a 3MB MP3 music file will count against your usage  cap, so in theory, a broadband service with an 8GB usage limit would  allow you to download over 2700 MP3s a month.
However, usage  limits do not apply to just file downloads. Visiting websites which have  large animated frames and numerous links, retrieving attachments and  sending/receiving emails, making VoIP calls, and using chat/IM services  all count towards your monthly limit - because of this, it is more  accurate to refer to a monthly cap as a usage limit. Usage limits can  vary from sizes as small as 1GB to 10GB to 50GB, or more.
Unlimited Downloading and Fair Usage Policies
Many  ISPs provide an unlimited monthly usage cap with their products,  theoretically allowing you to download as much as you like. However, any  'unlimited' usage limit will be governed by a fair usage policy. A fair  usage policy is in place to ensure that the internet service is not  compromised by the heavier users. As stated above, this can be a  particular problem on cable connections, as cable performance is  dependent with the amount of traffic in your local area, so if you live  in an area with several cable users, then your net performance can be  affected by this.
With an unlimited broadband package, there will  typically be an unspecified 'ceiling' limit, and once you exceed this  then your connection may be temporarily slowed down or even cut for the  remainder of the month; some ISPs have a policy where you will be  charged an additional fee should you go beyond such a limit. Most users  will rarely excessively use an unlimited usage allowance, but be sure to  read through the terms and conditions of each ISP's fair usage policies  before signing up.
Your browsing habits
As  with connection speeds, the size of a download limit is worth  considering in relation to your browsing habits. If you are planning on  downloading lots of music or having multiple users sharing the same broadband connection,  you will want to sign up for a package with a sizeable bandwidth  allowance so you can use the net for whatever reason without any  restrictions or slowdown. Casual and infrequent internet users find 2GB  per month more than sufficient for emailing and messaging, although you  may want something a bit bigger should you want to occasionally download  or watch video clips online.
Source from : 
broadband finder