Slow internet speeds on iMac running 10.10.3

Please read this whole message before doing anything.

This procedure is a diagnostic test. It’s unlikely to solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.

The purpose of the test is to determine whether the problem is caused by third-party software that loads automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.

Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you turn on the computer, and again when you log in.

Note: If FileVault is enabled in OS X 10.9 or earlier, or if a firmware password is set, or if the startup volume is a software RAID, you can’t do this. Ask for further instructions.

Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.

The login screen appears even if you usually login automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

Test while in safe mode. Same problem?

After testing, restart as usual (not in safe mode) and verify that you still have the problem. Post the results of the test.

You might want to perform an internet speed test to make sure your ISP isn't the problem. They'll be able to perform tests to rule out the ISP - then you can check out the modem, router, and computer (if necessary).

This happened to me just two weeks ago.

If you use iPhoto or Aperture, your photo library will automatically be converted to Photos format, and if you use iCloud Photos, a large amount of data may be uploaded to Apple. That will slow down Internet access for some time.

Launch the Activity Monitor application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad and start typing the name.

Select All Processes from the View menu, if not already selected, and also select the Network tab.

Click the heading of the Sent Bytes column in the process table to sort the entries by bandwidth usage. You may have to click it twice to get the highest value at the top. What is it, and what is the process?

Please answer as many of the following questions as you can. You may already have answered some of them; in that case, there's no need to repeat the answers.

• Restart the router and the broadband device, if they're separate. Any change?
• Are you connected to Ethernet as well as Wi-Fi? If so, disconnect the Ethernet cable or adapter and test.
• If possible, connect to the router with an Ethernet cable and turn off Wi-Fi. Any difference?
• If you can connect to more than one network, are they all the same?
• Are all network applications affected, or only some? If only some, which ones?
• Disconnect all other devices from the network. Any change?
• Start up in Recovery mode. From the OS X Utilities screen, select Get Help Online. A clean copy of Safari will launch. No plugins, such as Flash, will be available. Any difference?
• If possible, turn off Bluetooth and disconnect any USB 3 devices. Any difference?