A snapshot of the computing environment of 2008:
ISE 10.1's synthesizer (XST) has a low default limit for loop unrolling. If your VHDL/Verilog code contains large for-generate loops, you will hit "XST: 1391 - Loop count limit exceeded." You must manually increase the "Loop Count Limit" in Synthesis Properties to 2000 or higher. xilinx ise 10.1
For the Virtex-4 and Virtex-5 families, ISE 10.1 offered "Physical Synthesis" options in the Map phase. This allowed the software to optimize logic based on physical location—duplicating registers to reduce fanout or re-timing pipelines to meet clock frequency. This was a massive upgrade from version 8.x. A snapshot of the computing environment of 2008: