Megabits per second, or Mbps, reports the speed data is being transferred. The lowercase “b” indicates that the measurement is in bits, but speeds are sometimes expressed as bytes, with a capital “B.” Since it requires eight bits to make a single byte, the distinction between Mbps and MBps is quite large. Download speeds can be measured using bits per second, kilobits per second or megabits per second.
Bits and Bytes
Computers store and use information in groups of numbers, using binary number notation, or Base 2. Each bit is represented by a zero or one, and every eight bits are grouped together as a byte. A kilobyte is 1024 bytes, and a megabyte is 1024 kilobytes. When data is being transferred between computer devices, it is broken down into small units that can be checked for accuracy using a special byte of data called a checksum.
Modems were developed to transfer bit streams, or collections of databits, that could be reassembled as bytes. This allowed people to send text messages back and forth, or exchange programs, pictures or other data. Early modems were only able to reliably transmit small amounts of data at a time, and the modem speed reflected the bits per second, or bps. The baud rate, or transfer rate, began to be expressed in bps, and it was logical to simply add a qualifying counter as speeds increased. A 56K modem, for instance, is designed to deliver a maximum throughput of just over 56 Kbps, or 56 kilobits per second.
A wired network can run at speeds of more than 100 Mbps, and new data transfer methods allow even faster transfer rates, measured in Gbps, gigabits per second. Exchanging files over a wireless network connection is usually measured in megabits per second, or Mbps, and can transfer hundreds of megabits at a time.
Because of the way the Internet works, your download speed is affected by outside factors. The information you are downloading has to be transferred from the host location to you, but it is rarely a direct connection. Instead, the data get passed along from server to server, always looking for the shortest possible route to get to you. When the data is forced to take a circuitous path, your download speed will suffer, and you will experience a lower Mbps transfer rate.
Another item that can affect your real transfer speed compared to the apparent speed is the use of error correction software or a download manager. Although the two work much differently, they both attempt to maximize transfer rates across a network. Error correction devices use compression techniques to send more data at once, decoding the packets when they arrive. Download managers attempt to receive streams of data, not necessarily in the correct order, and then reassemble the parts. In both cases, the reported Mbps rate is adjusted to account for resending data, assembling packets and other file transfer maintenance.