What Is Data Transfer Rate?

Data transfer rate is comparable to traffic flow. In theory, the wider the highway and the higher the speed limit, the more traffic moves through. Just like traffic flow, which can be affected by obstructions, accidents and poorly designed highways, data transfer rate is subject to problems as well. Basic definitions, units, typical data transfer rates and comparisons will help define what factors make up a data transfer rate.

Definitions

In order to understand what data transfer rate is, some definitions need to be covered.

Bandwidth--the maximum rate at which data can be transmitted. This term is different from "data transfer rate."

Binary number system--a system based on the number 2; it uses "0" and "1" as its basic numbers; each position is either "off" or "on." All computers use binary numbers.

Bit--the most basic form of information; can be represented by the presence or absence of an electric current (binary "0" is "off"; binary "1" is "on").

Byte--eight bits; represents one character.

Data transfer rate--the rate at which data is sent between two computer devices.

Giga--metric prefix for "one billion."

Kilo--metric prefix for "one thousand." It is good to note that in computer terms, one kilobit is 1024 bits and not 1000 bits. This is because of the binary (base 2) number system.

Mega--metric prefix for "one million."

Throughput--same as "data transfer rate."

Tera--metric prefix for "one trillion."

Units of Measurement

Abbreviations:

bit--b (lower case "b")
byte--B (upper case "B")
kilobits--Kb
kilobytes--KB
megabits--Mb
megabytes--MB
gigabits--Gb
gigabytes--GB
kilobits per second--Kb/s
kilobytes per second--KB/s

The other metric prefixes follow this same pattern:

1 Kb = 1 kilobit (1024 bits)
1 Kb/s = 1 kilobit per second
1 KB = 1 kilobyte (1024 bytes; one megabit; 1,048,576 bits)
1 KB/s = 1 kilobyte per second
1 MB = 1024 kilobytes
1 GB = 1024 megabytes, 1,048,576 kilobytes

To advance to the next metric prefix, keep multiplying 1024 by itself for every group of three numbers after the first digit:

kilo: 1024
mega: 1024 x 1024
giga: 1024 x 1024 x 1024
tera: 1024 x 1024 x 1024 x 1024

Significance

Data transfer rates are important in choosing the right computer and peripherals. Peripherals include printers, modems, USB devices, disk drives and their controllers, fax machines and external disk drives.

The data transfer rate is also an important factor in choosing a network or Internet service provider (carrier). It should be considered with other factors, such as the carrier's dependability and equipment limitations.

Since data can be sent over various equipment and links ("hops"), the data transfer rate is usually dictated by the weakest (lowest) link. This can create a network "bottleneck." This happens regardless of how fast the other equipment is.

Typical Data Rates

Here are some typical data rates for common devices (lowercase "b" is "bits;" uppercase "B" is "bytes").

USB 1.1 (old USB standard): 12 Mb/s (1.5 MB/s) maximum
USB 2.0 (new USB standard): 480 Mb/s (60 MB/s) maximum
USB Flash Drive: 30 Mb/s (3.75 MB/s) typical
Internal Hard Drive: 30 Mb/s to 300 Mb/s (3.75 MB/s to 37.5 MB/s)
CD-ROM Drive at 48x write speed: 57.6 Mb/s (7.2 MB/s) maximum
DVD-ROM Drive at 8x write speed: 81.6 Mb/s (10.2 MB/s) maximum
Optical Fiber: 3.2 Gb/s (400 MB/s)
Ethernet (old standard): 10 Mb/s (1.25 MB/s) maximum
Dialup Connection: 56 kb/s (7 KB/s) maximum
DSL Connection: 320 kb/s to 800 kb/s (40 KB/s to 100 KB/s) typical
Cable Connection: 2.4 Mb/s (300 KB/s) typical

Fun Facts

The system with the highest data transfer rate as of 2006 is the Nippon Telegraph and Telephone system in Japan. It had an overall transfer rate of 14 terabits per second. That equates to 1.75 terabytes (1.75 TB/s); 1.75 trillion bytes. Put into perspective, that would be equivalent to transmitting about 200,000 typical MP3 files in one second, assuming that each file was 10 MB in size.

Of all transmission media, fiber optic cables give the best transfer rate.

The first computer network was called ARPANET. Its operation commenced on August 30, 1969, to link four university computers.

Typical download times for a 10 MB file:

Dialup at 7KB/s: 24 minutes
DSL at 100 KB/s: 1 minute, 40 seconds
Cable at 300 KB/s: 34 seconds

References

• Data Transfer Rate Calculator
• Data Transfer Rate Definition
• Information on USB Ports

Resources

• Good History of the Internet