PA running slow, is it my computer?

Ive got a old Imac and its running PA incredibly slowly. I'm running a 2007 imac, mountain lion OSX, 2.4 GHz intel core 2 duo, 6 GB DDR@ SDRAM, ATI Radeon HD 2600 Pro 256MB.

So my question, is the slowness a result of an incomplete alpha build for mac OSX or is this a computer issue. I can run other games fairly well like Starcraft ii and teamfortress ii. I was suprised at how slow PA is, seems to rack my processor.

Anyway any suggestions and advice is greatly appreciated, Thanks!!!!

1. an alpha build is by definition not polished yet.

2. you have an old computer, as evidenced by the fact you said it was old.

3. your CPU is pretty old (with regards to high-end gaming).

4. your GPU is absolutely terrible.

5. Starcraft 2 is incredibly scalable even on older hardware. As is the Source engine (and all derived games).

I hope this answers your questions

Update your graphics drivers, turn shadows off and play on small moons. Performance will improve as Uber start to optimise.