If you have more than one torrent downloading then they are assigned positions in the download queue. Normally a new torrent will be added to the bottom of the queue although this can be changed when adding a torrent in the options dialog.
You can also re-organize the download queue by dragging and dropping torrents as required, or by right-clicking and selecting the 'reposition' option.
The maximum number of active downloads is defined in the general Queue options - if you have more than this number of downloads the remainder will wait in a queued state until a slot becomes available (there are also options that permit stalled downloads not to be counted as active, so you may see extra downloads active in this case)
There are three options for ordering the downloads:
This is the default, download priority is based on the order that you manually set for the downloads.
Seed Count Based
Since 5711_B04 there has been the option to automatically order the downloads based on the number of seeds (and peers if seed counts are equal) that each download has.
For the rules to be effective it is important that you set a global download limit within Vuze - right click on the download speed indicator on bottom right of the status bar or go to Tools->Options->Transfer to set this. If you don't know your download limit run a speed test. The reason this is important is that when a limit is in place Vuze can easily determine if your download speed is optimized and therefore that there is no point in attempting further adjustment. The adjustment process requires that the potential download speed of downloads be tested - this can cause a transitory decrease in overall download rate.
It is only worth enabling this option if you have a number of incomplete downloads in a queued state.
The following options influence behavior:
- Download speed evaluation period: the number of seconds that a download will be allowed to run for at the top of the queue to assess its potential download speed
- Re-evaluate downloads: the number of minutes to wait before re-evaluating a download's potential speed. Enter zero to disable this.
Read the Azureus FAQ