This is slightly tangential to the Web development side of things but its interesting to note none the less since it affects how fast the website will have downloaded to the client machine, and be ready for our users to ... well.. use.
I was going to download a Mandriva Linux ISO image to install, and I noticed by download speed was only around 30KBps (Kilobytes per second) which considering my Internet connection is clocked at 4Mb (4 Megabits) by my ISP was rather strange. I figured out I was downloading from a far away mirror server, once I changed to a closer one, the download speed multiplied to around 350KBps. So I went from a download that was going to take 16 hours, to one that took only 30 minutes to complete.
But how can you tell your speed is not right, well that's what we will be talking about today.
When the internet first became publicly accessible, we had modems with blazing speeds of 9600 Kb/s, then 14400 Kb/s until they reached the modem cap of 56Kbps. Websites were pretty much text based up until the latter days of 36K modems when we started to get more and heavier graphics, flash animations made their debut, and videos and audios starting to trickle into the web consciousness.
But alas, the modems were sadly outclassed because they just weren't fast enough to keep up with the demands of the content. At this point Web developers had to keep a careful eye on how big the site would end up being, how many images were going to have to be downloaded, and how big these files were because the speed of the modems was limited, and you wouldn't want to have your users waiting for the page to load.
Today speeds have multiplied at least 10 times what they were then, but they still cause the same amount of confusion.
ISP's will tell you you have xMb (Megabits) of blazing speed but how does that actually translate into how fast your downloads will be, or how quickly your Youtube videos will start playing. In practice downloads are measured in bytes, while ISP's will use bits to promote their blazing bandwidths.
Lets take a regular 56k modem. That's 56000 bits per second of data transfer.
Since 1 byte equals 8 bits that modem was transferring at a "blazing" speed of 7000 bytes per second or about 7 kilobytes per second. For a reference, a regular text file is about 1 or 2KB. Low res images range in 30 to 50 KB range while mid range images have file sizes in the hundreds of kilobytes, and hi res images move into the thousands of kilobytes or what we know as Megabytes. So a website, with pictures, audio and text quickly starts to add up the download time. A single 200KB image which by today's standards is pretty small, would take about 30 seconds to download through our 56K modem. So for half a minute you'd sit there waiting for the picture to come up. Granted back then 200KB files were considered somewhat large so most WB developers had smaller images sacrificing quality, but imagine a website with more pictures, and code etc... you'd be waiting for a while before you had a fully downloaded website.
Fast forward a few yeas and we get MegaBit speed plans. These DSL plans basically tell you your plan will have a download speed of up to the specified number. That is X will be the maximum speed yo can expect from the connection. However, due to the way DSL works, the speed can't be guaranteed so you'll have a variance of speed. Still there should be an operational margin where you can feel you are getting what you are paying for.
Say your DSL is offering you a 4Mb Plan at $19.99. That's 4,000,000 (Four million)
bits per second maximum data transfer or 488 KiloBytes per second. You should be expecting a bit less than that, somewhere between 250 to 400 KBps; depending on where you are downloading from, is acceptable. Anything less and you can argue you are in the next lowest price package at 2Mb. It may vary from time to time, but as long as it stays more consistently in that range your o.k.
Online DSL speed tests calculate this by measuring how long it takes for you to download a specifically sized file.
If you want to try out your speed, here are a few sites that offer speed tests.
DslReports
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