I’m going to bring out the oldest metaphor I have to try and put a handle on how fast is fast. No math (ok, not much), but first just a teeny, tiny bit of computerese.
And, of all things, radio.
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Bandwidth started in radio
I need to start with the term’s origin in radio transmission. Bandwidth is, literally, the width of the band taken up by a radio transmission.
I know: not very helpful.
When you listen to an FM radio station — say 88.5 MHz on the dial — that 88.5 specifies the center frequency — 88.5 megahertz, or 88,500 kilohertz — on which that station transmits. In reality, that station has been allocated (approximately1) 150KHz of “band width”, meaning that it transmits in the range between 88,425 and 88,575 KHz.
More information — and in this case, greater fidelity — can be transmitted on a wider band. While AM radio has a bandwidth of approximately 20 KHz, and FM radio might be at 150KHz, analog television frequencies were allocated up to 6MHz to handle the additional information required for both video and audio signals.
Bandwidth in computing
Almost none of that applies to the way we use the term “bandwidth” when it comes to computing, except for the concept that greater bandwidth allows more information to be transmitted.
When it comes to our use here, bandwidth is simply the speed at which data is transferred, or more commonly, the maximum speed or capacity of a data connection. Speed is usually measured in bits per second.
- kbps – kilobits, or one thousand (1,000) bits per second
- mbps – megabits, or one million (1,000,000) bits per second
- gbps – gigabits, or one billion (1,000,000,000) bits per second
- tbps – terabits, or one trillion (1,000,000,000,000) bits per second
One bit, eight bits, and text
You probably know that a bit is a single “thing” that can be either 0 or 1. Nothing more, nothing less.
Everything in your computer, every document you read or write, every song you stream, every movie you watch on your digital TV, everything you communicate on the internet is nothing more than a collection of bits. Everything.
The bit is the very definition of digital.
Bits are commonly handled in groups of eight, called bytes. If you look at eight bits whose possible values are either 0 or 1 each, the collection can have up to 256 possible unique combinations.
Text on a computer — such as you’re reading here — is commonly represented as a single byte per character2. So if I type, “The quick brown fox jumped over the lazy dog,” (which is 44 characters, including spaces) it takes 44 bytes to store all the characters.
Now we’re ready to break out our metaphor: the Bible.
The Bible as a unit of bandwidth
This has nothing to do with the contents of the Bible. Believe in it or not as you see fit. This is about its size. You’ve probably seen one, perhaps even own one, and have a good sense for how big it feels, how hefty it is, and how long it might take to read it cover to cover.
The Bible is a fairly sizeable common frame of reference.
You can download the text of The Bible from project Gutenberg as plain text, meaning the file contains only the text of The Bible in its simplest form.
A text-only copy in this digital form is 4,452,519 bytes. For our purposes, I’m going to round that up to an even 5,000,000 bytes, or five megabytes.
Five megabytes at eight bits per byte is roughly 40,000,000 bits.
One Bible, 40 million bits.
Let’s compare some common bandwidth figures and see how long it would take to transfer The Bible at each of those rates.
|Connection Type||Common Bandwidth||One Bible Download|
|Old, slow, dial-up||28kbps||23 minutes|
|Max dial-up||56kbps||12 minutes|
|Very basic ADSL||768kbps||52 seconds|
|T-1 / DS1||1.5mbps||27 seconds|
|High-speed ADSL (example)||24mbps||1.7 seconds|
|Cable (example)||100mbps||0.4 seconds|
These are all approximations, meant only to be examples of orders of magnitude.
Your speed will almost certainly vary. These numbers assume you have 100% of your connection available to you (which is not true, due to overhead and potential connection sharing), and that the download is the only thing happening on the connection.
Typically, if you’re getting within 80-90% of these numbers, life is pretty good.
Testing your speed
Naturally, we don’t all go around downloading Bibles all day. Particularly if you’re on a fast connection, the difference between, say, 0.4 and 0.04 seconds might not be noticeable.
The best way to test your speed is by using one of several different speed test sites.
- DSL reports speed test
- Fast.com from Netflix (tests download only)
Each reports the speed of your connection in some multiple of bits per second.
Remember that any other device using your internet connection while you run the test will impact your results. The results — approximate to begin with — will be even more so if you have lots of other devices online.
Back to The Bible
100 million bits per second is a pretty abstract concept.
That this is the equivalent of downloading 150 copies of The Bible in one minute hopefully makes it more real.
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Footnotes & References
1: All of this is over-simplified for clarity. While there are many (many) details that pedants might want to see included, they’re generally not useful to address the question at hand.
2: There’s also now Unicode, which includes two-byte and even four-byte character representation for the thousands upon thousands of characters and symbols used internationally.
8 comments on “What is Bandwidth as It Applies to My Computer?”
Very well written, as always Leo.
Thank you for simplifying things like this for us non-techie types. Please add more articles in this simplified easy-to-understand form.
I learned from this in reverse. I knew what bandwidth meant as related to data transfer but I’ve wondered why it’s called bandwidth.
I tried that test and only got 14 mb/s. Seemed pretty slow on my 50mb/s connection. Then I remembered I’m using a VPN. I turned off the VPN and got 44mb/s. How you connect can make a big difference in bandwidth.
This was an outstanding teaching article. Leo, you do many things well. Thank you for your kindness to share in such a thoughtful way.
How fast or how slow… It relates to what someone is used to. Back in the 1940’s my parents would pick up the telephone receiver and wait for the Operator who would complete the call (45-60 seconds). My parents thought it was fast enough for them. In the late 1950’s we had a dial telephone (put your finger in the hole and rotate the dial). At 30 seconds it was fast enough for my parents. Then we had “touch-tone” in the 1980’s. Making a call took 5-8 seconds. Now all I do is speak the name or phone number and I hear the other phone ring almost instantaneously. Unfortunately doing “things” now has gotten so fast I don’t have time to make a sandwich or pour a drink.
I’m loath to say this, but I disagree with your descriptions. And you have some contradictions within the same paragraph.
The thing that is often quoted (I blame the marketing people in promoting their employer’s services for this) is bandwidth or capacity of a DSL service (this includes fibre) as a speed or rate of transmittal. It is not.
Data communications engineers will often use the phrase “width of the pipe” meaning how big the capacity of the “pipe” is. Speed is the *rate* at at which data travels through that pipe. Capacity is how much can be pushed through the pipe in a given time. A DSL service having a capacity of 10Mbps will have more or less the same speed as a 20Mbps pipe but because your downloads arrive in less time they have more capacity on that pipe.
A real life example can be seen by gamers (some of whom make significant incomes) who will go to great lengths to use an ISP with the lowest latency, which reflects more accurately speed but even this is variable because you are using a shared public service. A good indication of the *speed* of a circuit is to use the ping or traceroute commands to see how long in milliseconds these small packets of data take to go on their route to the target and return to you. If it is low say less than 20 milliseconds then for this sort of service is good. If above 50 then not so good, but conditions change.
The analogy of a motorway/freeway & in most countries they have speed limits (and most people obey them). A two lane road will have set maximum capacity of vehicles & the maximum speed limits. Increase the two laner to a three laner and you’ll get more vehicles because you’ve increased the bandwidth or capacity of the road but not increased the speed limit.
Having been one of your readers for many years now & a career in computing & in retirement of in excess of 50 years, I have been grateful for some of your insights especially in the area of backups (on & off site) as I said at the start of this that I was loath to write this, but even before the internet we had the selling of leased circuits that sometimes were promoted on bandwidth as if it were speed.
A couple of comments. First, Harry B is technically correct in his definitions of bandwidth, speed, capacity, but as Leo described the computing network industry has chosen to use the term “bandwidth” for speed or rate of data transfer. It is what it is.
Second, there is one aspect of speed tests that hasn’t been mentioned yet: speed test is very dependent on the mirror site location, which is the location with which data is transferred to measure the data transfer rate. If the mirror site is physically close to your location then the reported speed is likely to be high, otherwise it will slower. Try this test where you can choose a different mirror site in the world: http://www.speedguide.net/speedtest/.
Other variables in a speed measurement are time of day, your browser, your OS, your network equipment (e.g. router, computer, WiFi or wire), the type of test (data packet size) and the test website that you use. Curiously, the Netflix site (fast.com) always gives a higher download speeds, as does your own ISP’s speed test.
Bottom line is that these speed tests are highly variable and unreliable. The good news is that if your network response is too slow for you, you’ll know it.