Slow Downloads and Connection to Content Servers

Is your download actually slow?

• Comparing Steam download speeds to your Internet connection speed:
  
  Internet and other network connection speeds are typically measured in multiples of bits per second. However, Steam downloads, like many other file downloads, are measured in multiples of bytes per second. A byte is a group of 8 bits.
  To compare your Steam download speed to your connection speed, multiply your Steam download speed by 8. For example, if you are getting 768KB/s (kilobytes per second) as your Steam download speed, you are getting 6144Kb/s (kilobits per second) or 6 megabits per second download speed according to most Internet service providers.
  Example download speed conversions
  
  

  Advertised Connection Speed	Est. Max Steam Download Speed
  3 megabits/second	384 KB/S
  5 megabits/second	640 KB/S
  15 megabits/second	1.9 MB/S
  20 megabits/second	2.5 MB/S
  30 megabits/second	3.75 MB/S
  50 megabits/second	6.25 MB/S

• What is your actual Internet connection speed?
  
  The speed displayed in your System Tray or network connection properties is typically the speed you are connected to your local area network (LAN) and does not represent the speed you are connected to the Internet at. Please refer to the materials for your connection plan or contact your Internet service provider (ISP) for information on your connection speed. You can also use one of the numerous speed testing sites available online such as SpeedTest or DSLReports to test your connection speed.
  
  

Content Servers

Steam uses content servers that are located all over the world. Steam attempts to select the best content server based on your location.  If Steam downloads are going slower than expected, please double check your current download region:

1. Start Steam
2. Go to Steam > Settings > Downloads tab
3. Under Download region, select the region that you are in or that is closest to you.
4. You can also try various regions near your location to see if a better connection is available.
    

Third Party Applications

Some third-party applications such as ESET NOD32 Anti-Virus can cause Steam to use incorrect content servers. Any sort of Internet security and/or packet filtering software may have a similar affect. This can also lead to connection issues.
If you are not using NOD32 but a different program might be causing the issue, please follow the Programs Which Interfere with Steam guide to test the issue.
For NOD32, there is a work-around that may help:

1. Go to NOD32's settings
2. Under Antivirus and antispyware, locate Web access protection
3. Find Web browsers and locate Steam.exe
4. Click the box until a red X is displayed
5. Click Ok and close the settings

For example:

Rename the ClientRegistry.blob

Your ClientRegistry.blob file, located in the Steam directory (C:\Program Files\Steam\ by default), stores the location information for Steam to use in order to select the best content server. After disabling your background applications, please see the ClientRegistry.blob guide.

Network Connectivity

Please follow these directions to make sure the correct ports are open and double check the list of ISP's that are known to have issues with Steam: Troubleshooting Network Connectivity.

Connection Rate

Ensure that your Steam connection rate is set appropriately. For more information, please see Setting Client Rates.

Source:  https://support.steampowered.com/kb_article.php?ref=9498-WPDF-3220