Valve, the makers of "Portal," recommend that you have at least 1GB of RAM in your computer. A fast processor cannot help very much if you do not have enough RAM because your computer will not be able to efficiently use the data it is processing. The absolute minimum amount of RAM that your computer needs to run Portal is 512MB. Keep in mind that other programs that are running on your computer consume RAM as well.
A number of reasons can cause the video game "Portal" to run slowly even if you have a dual-core processor. The game's performance depends on factors other than how quickly raw data can be processed. By learning about these, you can more easily troubleshoot performance issues as they arise.
If you have many programs running in the background while you play "Portal," such as a Web browser playing Internet radio, for example, "Portal" will run slowly. The more RAM you have, the more programs you can afford to run in the background. For best performance, close all nonessential programs through the Task Manager. Right-click the task bar and then click "Start Task Manager." Click the "Processes" tab when it loads, select a program you don't need and then click "End Process."
Another very important consideration is the type of video card that you have. At a minimum, you need a video card that supports DirectX version 8.1. The game will run slowly or not at all if you do not meet this minimum requirement. A dual-core processor cannot make up for a deficient video card because the video card contains special hardware that the game needs to render smooth video. You can use Device Manager to see what type of video card you have. Open Device Manager by clicking "Start," typing "Device Manager" into the search bar and then pressing "Enter." Next, click the "Display Adapters" entry located on the left-hand side.
There are a few steps that you can take in-game to improve the performance of "Portal." If you exit to the main menu, you will see a tab entitled "Settings." Click this, and then click "Video." Note the current resolution and then select the next lowest. With a smaller resolution, your video card will have less area to render. You can also increase performance by setting the "Detail" setting to "Low." Experiment with these settings until you achieve a balance between detailed graphics and better performance.