The only downside to Clozure CL that I found was the fact that it requires SSE2 instruction support from the processor. There are still some processors around

The only downside to Clozure CL that I found was the fact that it requires SSE2 instruction support from the processor. There are still some processors around that don't support that -- which can be a bummer if you want to use Clozure CL on one of those machines. Unfortunately, one doesn't always have the option of upgrading the hardware to get around that. I don't think the developers have worked around that, though I have seen some conversation about it in the past. My limited Google searches on the subject today didn't suggest that anything has changed since the last time I looked at it. Edit: Oh, duh, I already said all of this about 4 1/2 years ago: https://news.ycombinator.com/item?id=1804415 https://news.ycombinator.com/item?id=1804415 Visiting the system requirements page again suggests the limitation still exists: http://trac.clozure.com/ccl/wiki/SystemRequirements http://trac.clozure.com/ccl/wiki/SystemRequirements