Official specs from Steam

Portal 2 system requirements

Minimum and recommended PC specs as listed by the developer on Steam. Native Linux build available.

Minimum

OS *Windows 7 / Vista / XP
Processor3.0 GHz P4, Dual Core 2.0 (or higher) or AMD64X2 (or higher)
Memory2 GB RAM
GraphicsVideo card must be 128 MB or more and with support for Pixel Shader 2.0b (ATI Radeon X800 or higher / NVIDIA GeForce 7600 or higher / Intel HD Graphics 2000 or higher).
DirectXVersion 9.0c
Storage8 GB available space
Sound CardDirectX 9.0c compatible

FAQ

What graphics card do I need for Portal 2?

Minimum: Video card must be 128 MB or more and with support for Pixel Shader 2.0b (ATI Radeon X800 or higher / NVIDIA GeForce 7600 or higher / Intel HD Graphics 2000 or higher)..

How much RAM does Portal 2 need?

Portal 2 needs 2 GB RAM at minimum.

How big is Portal 2?

Portal 2 requires 8 GB available space.

Does Portal 2 run on Mac or Steam Deck/Linux?

There is no native macOS version. A native Linux build is available.