RFC 2068 stipulates two concurrent download sessions. IE allows two such sessions (plus one queued). To increase this to 10, in:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
add the following DWORD values:
Value name: MaxConnectionsPer1_0Server
Value data: 10
Base: Decimal
Value Name: MaxConnectionsPerServer
Value data: 10
Base: Decimal
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings]
"MaxConnectionsPer1_0Server"=dword:00000010
"MaxConnectionsPerServer"=dword:00000010