Can Hashcat Effectively Use a 4090 on a PCIe x1 2.0 Slot?

[thealexandra]

Hai!

I know this might sound like a dumb question, but I’ve done a lot of searching and even read through Hashcat's official documentation on PCIe bandwidth. Still, I keep running into conflicting opinions on various forum posts, so I wanted to get some real clarification.

I'm building a system on an older motherboard for specific reasons, and while it has limited PCIe lanes, I’d like to use it for serious GPU compute tasks, including Hashcat, among other things. My main question is whether a high-performance GPU like the RTX 4090 can still be effectively utilized through a PCIe x1 slot for Hashcat workloads. I understand that Hashcat primarily loads data into GPU memory, so in theory, PCIe bandwidth shouldn't be a huge bottleneck, especially for brute-force or compute-heavy work. But I've seen users mention that certain operations (like large wordlists or heavy rule-based attacks) could suffer, while others say the difference is negligible.

To cut to the chase: has anyone actually tested this? I would really love to see benchmark comparisons or real-world examples. Here's a breakdown of the kinds of workloads I'm curious about (assume hash mode = MD5 for consistency):

• Pure brute-force attack like ?b?b?b?b
  
• Giant wordlist with no rules
  
• Small wordlist with lots of rules
  
• Giant wordlist with lots of rules
  

I’m not looking to stir debate, I’d just love to know how much of a hit (if any) I should expect in these scenarios when running a high-end GPU on a bottlenecked slot. Actual benchmarks or experience-based insight would be incredibly helpful in planning out my build.

Thanks for reading!