22 June 2011

Bits Vs Bytes and your internet or network connection speed.

Alright, lets get to the basics, bits and bytes are both a measure of data size, however each is rather different. To differentiate the two, bits are expressed as say 34 kilobits will be 34kb. 34 kilo bytes will be expressed as 34KB. Note the capitals and the how bits are lower case and bytes are upper case. 

File size on disc is always expressed in bytes, so maybe you have a song that is 3.4MB (3.4 x 1024 million bytes) in size, and you want to transfer it over your internet connection. Say, a 512kbps (512x 1000 bits...note that bits are expressed as 1000, bytes in 1024) ADSL line. You calculate at half a mb per second, it should take 6-7 seconds.

Then you rage out when you see your connection hitting a wall at 62KBPS. You call your ISP and fume and throw venom at the costumer service guy.

Guess what?! Network connection speeds are always expressed in bits per second! not in bytes per second! To convert kbps to KBPS use the following [Kilobits per second times 1000) divided by 8)) divided 1024 ]
512 times 1000 = 512000. 512000 divided by 8 = 64000. 64000 divided by 1024 = 62.5. Or you can make it easier and use [kbps times 0.1220703125 = KBPS]
512 times 0.1220703125 = 62.5.

Thus your upper limit on data transfer speeds is actually is 62.5Kilobytes per second. Not 512 kilobytes per second. Thats your upper limit! depending on how far you from the telco's central office, how good your local loop of copper wire is, if your ISP or telco does throttling or traffic shaping, and your network over head. (things like unroutable packets pinging around til their TTL is up, and Internet control message protocol packets) You will can expect your rate to be at least 20% lower then your maximum calculated transfer speed...of course if your ISP is nice, you may exceed it if they are not strict on throttling it.

The kind of tricky thing is, network connection speeds are kbps/mbps. Files sizes are in KB/MB..and when you see a download or upload rate...its in KBPS or MBPS, because thats how file size is measured. But that can cause you confusion if you don't know that and are paying for 512kbps and get upset that you can't exceed 62.5KBPS...just remember connection speed= bits per second, download rate, bytes per second.

Hopefully my above explanation has cleared up that common source of computing/networking frustration.

Another note is, if you are using a hub/switch/router to share your connection, the total available bandwidth is shared with the other computers. So if you are downloading a movie while your room-mate is streaming in audio, both of you will notice a drop in connection speed as it is divided amongst you.
Your rated speed is the theoretical maximum, you will generally, never be able to hit that speed unless your inside the telco's central office or the internet exchange where your ISP peers off...not unless your ISP gives you some wiggle room by setting your maximum higher then advertised so you can hit the advertised speed.

We here at interconnect hope this article has cleared some confusion, as we get asked about this topic a lot.
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kilobits vs kilobytes by DD-49 network is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
Based on a work at network-computer-info.blogspot.com.