Regarding older systems

So when PA is released and everything will it actually be able to run on older systems? Or his it going to have a high needed systems specifications?

Windows XP - Confirmed no.

I'm not talking about operating systems I'm talking about just system specifications.

Have you check the current recommended specs using the Steam Early Access page?

Without some examples it's hard to answer really, 'old' is pretty relative in terms of system specs.

Mike

Let's say in theory this game might have very low CPU usage on client and it's technically possible to replace advanced textures/models/effects with something not such hardware demanding. PA need quite a lot of memory, but I guess there also tons of ways RAM usage might be decreased.

Practically everything not as good:

• Older systems have DDR2 and bunch of other old standards and as result they just have much slower RAM. This why any 2 core i3 in $300 laptop will easily beat your desktop monster from 2006.
  
• Usually it's just pretty hard to support old hardware because devs are not working on 5 years old computers and fixing of each bug require to get such hardware and test game on it.
• AMD abandoned GPU of 2XXX 3XXX 4XXX series year ago only after 3-3.5 years when 4XXX was released. As result there is ton of issues in their legacy drivers.
• Many old GPUs just don't have functionality and require tons of extra work to support.
  So actually PA can work on some of AMD HD2XXX and newer as well as Nvidia Geforce 8XXX and newer.
• Most of people with really old hardware still using old OSes like XP, so it's mean even if devs spend lot of time on such optimizations those people won't buy game.

So there is just too many small details which make optimizations for outdated hardware nearly impossible.

PS: Still PA actually work fairly well on brand new low-end hardware like Celeron/Pentium laptops. Few weeks ago I configured $400 laptop with Pentium Dual-Core 2020M and Intel HD2500 and even on Linux performance was great and on Windows it's probably will be +20% to graphics performance.