System Specs

General

Better hardware helps, but sometimes in non-obvious ways:

• A fast (per core) CPU. Dual-core may help, but given the limitations of the Unity engine, more will do very little.
• A dedicated graphics card (desktops & larger laptops)

KSP currently (1.0.2) does not make much use of multi core CPU's. You will get a better performance with a CPU with good single core performance and high clock speed. At some point the game also seems to hit a limit on whats possible so there's not much difference between 2 high-end CPUs running an extremely big space station.

The same is true of spacecraft design:

• Fewer parts, especially struts.
• Avoid highly detailed 3rd party parts.
• Keep installed part counts low.

Current Paid (1.0.2)

Minimum:

• Processor:Core 2 Duo
• Memory:3 GB RAM
• Graphics:SM3 512MB VRAM
• Hard Drive:1 GB HD space
• One of the following OSes:
  • Windows XP, 7 or 8
  • Mac OS X 10.6 or higher
  • A Debian-based Linux distro. The game will also work with many other distros (such as Ubuntu, Mint, Arch, Fedora(rpm), or Gentoo).

Recommended:

• Processor:Core i5
• Memory:4 GB RAM
• Graphics:SM4 1GB VRAM
• Hard Drive:2 GB HD space
• One of the following OSes:
  • Windows XP, Vista, 7 or 8
  • Mac OS X 10.6 or higher
  • A Debian-based Linux distro. The game will also work with many other distros (such as Ubuntu, Mint, Arch, Fedora(rpm), or Gentoo).

e.g. mid-2009 MacBook Pro w/ dedicated graphics

Current Demo (0.18.3)

Minimum:

• Intel Core2Duo or equivalent.
• 2 GB of RAM (4 recommended because it can use up to 1700 megs).
• Intel HD3000 or better (Dedicated video card highly recommended).
• 1GB Free HD space
• One of the following OSes:
  • Windows XP, Vista, 7 or 8
  • Mac OS X 10.6 or higher
  • A Debian-based Linux distro. The game will also work with many other distros (such as Ubuntu, Mint, Arch, Fedora(rpm), or Gentoo).

This is the absolute minimum to get a playable (if slow) game with smallish rockets, however. A faster system will greatly enhance one's experience.