Bits, Bytes and Internet Speeds:
A Little History
All computers use digital processors that communicate using binary bits. The name 'bit' is an abbreviation of b(inary dig)it.
In decimal, each digit can take the values 0 through 9, however a bit is a basic binary value that can only have the value of one or zero. The state of a bit is commonly referred to as being a 1 (ON) or a 0 (OFF).
Computers generally use the Byte, which consists of 8 bits for storing data. Using the binary numeral system an 8 bit Byte can hold the values of 0 through 255.
Broadband Internet providers market their services in bits per second, not to be confused with Bytes per second. Remember there are eight bits in a Byte. For example a 3 Mbps DSL connection can download at 3 million bits per second or 375 thousand Bytes per second.
Most home broadband services are also asymmetric, which simply means that more of the total bandwidth is dedicated to the download channel than to the upload. This is because most home users want to download far more data than they upload. For example you may have an ADSL plan that provides 3 Mbps download speed and 1 Mbps upload speed.
While Broadband services are measured in bits, computer files are not. They are measured in Bytes, Kilobytes, Megabytes, etc. To further confuse the issue a Megabyte has two different values depending on the context. For example computer hard drives are marketed using decimal values. A 500 MB drive can hold 500 million Bytes, however when you look at the size in Windows you will see 476.8 MB. This is due to the fact that the computer uses binary values such as 1024 for 1 Kilobyte, then 1024 Kilobytes for 1 Megabyte and 1024 Megabytes for 1 Gigabyte.
Estimate Your Download Time
Let's say you want to download an ISO image of a DVD containing Microsoft security updates and the file size is 3.4 GB. http://www.microsoft.com/en-us/download/details.aspx?id=34953
How long will it take to download 3.4 Gigabytes using your 3 Mbps DSL connection?
First off, let me state that there is a lot of overhead involved when downloading files from the Internet. You have to factor in the speed and load of the server that you are attempting to download from. The file may be located on a server in another country. Your connection may have to be routed through multiple hops (different locations) to reach the download server. Many people may be trying to download the same file at the same time
A good rule of thumb is to allow at least 25% for overhead in the transfer.
Let's do the math!
You need to download a 3.4 GB file from the Internet.
1 Gigabyte = 1,073,741,824 Bytes
3.4 GB is approximately equal to 3,651,000,000 Bytes
A Byte is 8 Bits, so you need to download 29,208,000,000 Bits
Your 3 Mbps DSL connection can download 3,000,000 Bits per second.
If you divide 29,208,000,000 by 3,000,000 you get 9736 seconds.
9736 divided by 60 = 162 Minutes
Let's account for overhead. 162 times 1.25 (25%) = 203 Minutes
It will take approximately 3 Hours and 23 Minutes to complete your 3.4 GB download using a 3 Mbps DSL Internet connection.
Average File Sizes*
- Document - 100 KB
- Spreadsheet - 300 KB
- JPEG Digital Photo - 2 MB
- MP3 Music Song - 4 MB
- MPEG Feature Length Film - 600 MB
- CD Image - 750 MB
- DVD5 Image - 4.7 GB
- DVD9 (Dual Layer) Image - 8.5 GB
- Blu-Ray Disk Image - 25 – 50 GB
*Note: These are average sizes. Exact file size will vary considerably depending on the specific content of your files.
Average Download Times (25% Overhead)
56 Kbps Dial-Up
- 100 KB Doc File – 18 Seconds
- 4 MB MP3 Song – 12.5 Minutes
- 750 MB CD Image – 39 Hours
1.5 Mbps DSL*
- 100 KB Doc File – 1 Second
- 4 MB MP3 Song – 28 Seconds
- 750 MB CD Image – 1.5 Hours
- 4.7 GB DVD Image – 9.3 Hours
10 Mbps ADSL2+/Cable/Fiber*
- 4 MB MP3 Song – 4 Seconds
- 750 MB CD Image – 13 Minutes
- 4.7 GB DVD Image – 1.4 Hours
- 25 GB Blu-Ray Image – 7.5 Hours
50 Mbps Cable/Fiber*
- 4 MB MP3 Song – 1 Second
- 750 MB CD Image – 2.6 Minutes
- 4.7 GB DVD Image – 16.8 Minutes
- 25 GB Blu-Ray Image – 1.5 Hours
*Note: Broadband delivery technologies encompass a wide range of speeds.
You can determine your Internet speed here. http://speedtest.net
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Bits, Bytes and Internet Speeds
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