Measuring Speed :
There are two measures for the size of a file: bits (b) and bytes (B). Communication engineers think in terms of transferring bits, whereas computer users think in terms of file sizes, which are usually measured in Bytes (such as kilobytes, megabytes, etc). There are eight bits to one byte.
The data rate determines how long it will take to transfer a file. The larger the file, the longer it takes, because there is more information to transfer. Data transfer rates are measured in thousands of bits per second (kbps) or millions of bits per second (Mbps). Notice, that in the kbps acronym, a lower case k is used instead of the upper case K. This is because when talking about the transfer of data, most engineers round the number down. So a kbps actually refers to the transfer of 1000 bits of information in one second, whereas a Kbps would refer to the transfer of 1024 bits of information in one second. A DSL or a cable modem can operate in ranges of 512 kbps, 2 Mbps or higher depending on the technology being used.
Download Times:
Calculated download times are theoretical and depend on cable connection, computer processor speed and other overheads. To get an estimate of the length of time it takes to download a file, divide the file size by the data rate. For example, how long will it take to transfer a low resolution digital photo of 256KB via a 512kbps cable connection? First step, convert the file size into bits: 8 x 256 x 1024 = 2097152 bits. 256KB corresponds to 2097 kb. Notice that the 2097152 is rounded to the nearest 1000, so lower case k is used. The download time is then 2097 kb divided by 512 kbps, which equates to approximately 4 seconds.
