When a Faster Computer Can't Speed Up CAD

We recently worked with a client who had an AutoCAD .DWG file that was running slow. Super slow. Just to open the file took at least 30 seconds, which feels like an eternity when you’re working on a project. Usually, AutoCAD files open in a few seconds on a modern PC.

The client was understandably frustrated, and asked us to investigate. Was something wrong with his computer? Did he need more memory or a faster video card?

I was immediately suspicious. I knew this client had a powerful computer, even though it was about 3 years old. I also knew that the drafting typically done in AutoCAD isn’t that resource-intense compared to other types of design work we seem, such as 3D modelling in Revit. The client’s PC should be able to handle pretty much anything in AutoCAD.

My first question was whether the AutoCAD issues were file-specific. I examined the affected file, which we’ll call Problem File A, and found it was about 20MB. That’s quite big for AutoCAD, but not yet in the realm of an absurdly large .DWG. I asked the client if he had another large project that wasn’t having issues, and he showed me Known Good File B, which opened in just 2-3 seconds despite being about the same file size.

So, it appeared the issues were indeed file-specific.

Checking Resource Use

I wanted to be sure we didn’t have a resource usage issue. I opened Windows Task Manager on the client’s computer and once again opened Problem File A, then Known Good File B while watching Task Manager on a second monitor. As I suspected, resource use stayed low. The system was only using about 20% of its processing power, 20% of its memory, and basically zero video card resources.

I also made sure that the .DWG file was saved locally, instead of being accessed over a network.

Lastly, I ran Process Monitor to check for a smoking gun, like a timeout trying to access a non-existent file path.

The Windows Task Manager can be used to show system resource use

Everything looked normal so far.

Can An Old PC Compare?

Since hardware resource use didn’t seem to be an issue, I decided to ask the client for a copy of the Problematic File and the Known Good file and test opening them on an older computer at our office. I happened to have an older PC that another client in the architecture field asked us to wipe and recycle for them, but hadn’t made its way to our recyling partner yet.

The test would tell me two things:

1. If the file performance was similar on the older and less powerful computer, we would know hardware likely wasn’t the issue
2. Since I was going to load a fresh copy of Windows and a fresh install of AutoCAD on the test PC, that would rule out any software corruption or misconfiguration

Here’s a comparison of the hardware in our client’s PC vs. our test PC:

The storage is not listed, but both were using Samsung 980 Pro NVMe drives. The CPU and Video scores are from cpubenchmark.net.

Test Results

As seen above, our test PC was much less powerful than the client’s computer.

However, the results on the test PC showed that the **AutoCAD file performance ** was about the same as on the client’s PC:

• Sample files included with AutoCAD: opened instantly
• Known Good File B: opened in 2-3 seconds
• Problematic File A: opened in 25-30 seconds

Therefore. how fast a computer was being used didn’t have much effect on the performance of these AutoCAD files.

If the available computing power mattered, I would have expected to see slower open times on the slow test PC. Even if Problematic File A had inherent file issues, perhaps the open times would have been proportional. For example, all files could have taken twice as long to open on the slow PC. That wasn’t the case; the open times were the same as on the fast computer.

Software Limitations

So, what was the problem, then?

For one thing, AutoCAD isn’t always able to make very efficient use of available hardware resources. For example, AutoCAD still performs many tasks in single-threaded mode. You may have heard of computer processors having lots of cores. Single-threading means AutoCAD can only use one core at a time, no matter how many cores are actually available. While single-threading isn’t necessarily a bad thing, it’s noteworthy that AutocAD is almost exclusively single-threaded.

In this case, the issues were specific to the problematic file. Having a faster computer would not have made the AutoCAD files faster! Instead, the client needed to look at the inner workings of the file.

While it’s beyond the scope of this article to optimizing AutoCAD files, some common tips are:

• Run the AUDIT and PURGE command
• Check for excessive or misused blocks
• Check for missing or excessive XREFS
• Try exporting (WBLOCK) to a new file
• Try copy-pasting content to a new file, as a test

IT Services for Vermont Designers, Architects, and Engineers

Green Mountain IT Solutions has extensive experiece serving design professionals, especially in the AEC industry. We are experienced with AutoCAD, Revit, SketchUp, Bluebeam Revu, SOLIDWORKS, and other common design software.

Contact us today for a free IT consultation for your design firm.