Hi, Need.

Until you delete something that won't fit in the remaining space.  Then
enough older items are permanently deleted to make room for the new.

I don't know how Vista decides WHICH older items to dump:  the oldest?  the
biggest?

RC

It depends on how much space you allocate for the Recycle Bin. The recycle
bin works a bit different than it did in XP.
In XP you set the size as a percentage of the total disk space, the default
was 10 percent. But hard drives have gotten so large, that this meant the
amount of space allocated to the recycle bin could be 50GB on a 500GB hard
drive.

Vista has changed this so that the user can set the amount of allocated
space in Megabytes. The default setting is approximately 5%. You can set the
allocated space by right clicking the Recycle Bin and selecting Properties.
If you have multiple drives/partitions, you can set the amount of allocated
space for each drive/partition.

According to the testing that I have done, if you attempt to delete a file
that is a lot larger than the allocated space, you will get a message that
the file cannot be moved to the RB and you will be given an option to
permanently delete the file. There is a buffer that allows the allocated
space to be exceeded, but this varies and only seems to work if you are
deleting small files. Once the allocated space is exceeded, files may be
removed from the RB without any warning. The files that are removed appear
to be the oldest files in the RB, so it is a FIFO action. (First In, First
Out)

Be warned, this behavior is not always predictable! I have set the allocated
space to 300MB and then deleted 4 files that are each 100MB and 3 of the
files were moved to the RB, but the 4th file was permanently deleted,
without any warning.

Since I depend heavily on the RB, I usually set the allocated space to a
high amount, like 10% of the free space on the drive. YMMV.