Want to replace 2 existing GPU with 2 Highend GPU, how to know how many usable lanes after that av.?

[PeroVV]

Hi, I have installed 2x GFX NVIDIA T1000 8GB in WORK STATION - HP Z6 TWR G5 A, AMD Ryzen Threadripper PRO 7955WX Socket.

I want to replace it with 2x Nvidia Quadro RTX A5000.

How can I know how much of free usable lanes i have on available  to support it with this CPU and configuration, in some parts of the documentation mention virtual lanes that are not defined anywhere, what does that mean and how do you manage or calculate them?

[NonSequitur777]

@PeroVV,

Welcome to our HP Community forum!

Outstanding question -the HP Z6 G5 A Workstation with the AMD Ryzen Threadripper PRO 7955WX is a powerful setup, and upgrading to 2x NVIDIA RTX A5000 is definitely a serious move. Here's what you need to know about PCIe lanes and how to evaluate your current and planned GPU setup:

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PCIe Lane Breakdown:

The Threadripper PRO 7955WX provides 128 PCIe 5.0 lanes, which is excellent for multi-GPU setups. However, how those lanes are allocated and connected depends on the motherboard layout and platform design -not all 128 are necessarily available for use by GPUs.

In most workstation-class systems:

• Each full x16 slot used for a GPU will ideally draw 16 lanes.

• If the motherboard supports bifurcation, some slots may operate at x8 when two devices share a set of lanes.

• The chipset and onboard devices (USB, SATA, M.2 NVMe SSD, network controllers, etc.) also consume some PCIe lanes.

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What Are “Virtual Lanes”?

The term “virtual lanes” isn’t official PCIe terminology. In some OEM or BIOS contexts, it may refer to:

• Dynamic lane assignment (where devices get assigned lanes based on presence/configuration).

• I/O virtualization technologies like SR-IOV (Single Root I/O Virtualization), where virtual functions share access to physical hardware.

• Or it could simply reflect marketing language to describe logical partitions of bandwidth, not actual PCIe lanes.

This can get confusing, so it's best to consult the HP Z6 G5 A QuickSpecs (see above) or Service Manual, which often includes slot-by-slot electrical specs (like x16/x8) based on configuration.

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How to Proceed:

To ensure full performance for 2x RTX A5000 cards, you should:

1. Check the HP motherboard diagram (or BIOS setup) to confirm which slots are wired for full x16.

2. Ensure adequate cooling and power supply — 2x A5000 cards can draw around 450W+ combined, so you’ll want a 1000W+ PSU.

3. If exact PCIe lane assignments aren’t shown, HP Support or a Service Manual can clarify your board’s capabilities.

4. In Linux, you can run the following to check current PCIe device lanes:

   lspci -vv | grep -i width

   This tells you what speed and width each device is running at.

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Let me know if you'd like help interpreting slot assignments from the documentation -happy to assist!

One more thing:

Power Requirements: 2x NVIDIA RTX A5000:

Each NVIDIA RTX A5000 has a TDP (thermal design power) of 230-watt. So, two of them together will draw 460-watt minimum.

However, that’s just for the GPUs alone -not accounting for the CPU, motherboard, memory, storage, or peripherals.

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Estimated Total System Power Draw:

Here’s a ballpark estimate for the full system with 2x RTX A5000:

So realistically, you’re approaching 900-watt under full load, maybe a bit more with lots of drives or USB devices and such.

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HP Z6 G5 A PSU Capability:

The HP Z6 G5 A Workstation offers different PSU configurations, depending on model:

• Common PSU options include:

  • 850-watt Platinum

  • 1125-watt Platinum (optional upgrade for high-end configurations)

If your Z6 G5 A came with dual GPUs or was intended for heavy GPU workloads, it likely has the 1125-watt PSU, which is sufficient for your planned setup.

But if it has the 850-watt PSU, you’d be cutting it way too close -and a PSU upgrade is necessary, especially if you're also running a high-core-count Threadripper CPU such as the 7955WX.

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Recommendation:

• Check your exact PSU wattage -it should be labeled inside the chassis or visible via HP's BIOS/Diagnostics or via dmidecode in Linux.

• If it’s <1,000-watt, consider upgrading to HP's 1125-watt PSU.

• Ensure both GPUs get dedicated 8-pin PCIe power connectors — using daisy-chained power can risk instability under load.

Kind Regards,

NonSequitur777

[PeroVV]

Thank You on very nice explanation.

The reason why I came with this question was technical specification of CPU which say "

AMD  Thread ripper Pro 7955WX (4.5 GHz base clock, up to 5.3 GHz max boost clock, 64 MB L3 cache, 16 cores, 32 threads)". According to this it looks like it say that this type of CPU support only 32 threads what I suppose it is lanes.

In this case i could be very fast without enough lanes if I put 2x A5000 GPU and some other cards ?

After that I saw mentioning of virtual lanes what is not that so clear to me how we can calculate them ?

[NonSequitur777]

@PeroVV,

Thank you for the follow-up -and you're absolutely asking the right questions!

Let’s clear up the threads vs. PCIe lanes confusion first:

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🔹Threads:

• Threads are related to the CPU's processing ability, not PCIe lanes.

• Your Threadripper PRO 7955WX has:

  • 16 cores

  • 32 threads (thanks to simultaneous multithreading — SMT).

• Threads handle tasks/instructions for software applications and the operating system.

• They have nothing directly to do with PCIe lanes or how devices are connected.

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🔹PCIe Lanes:

• PCIe lanes are high-speed data highways between the CPU/chipset and connected devices (GPU, SSDs, etc.).

• The Threadripper PRO 7955WX supports 128 PCIe Gen 5 lanes (which is a ton).

• These lanes are meant for hardware communication — not software thread processing.

• In workstation motherboards like the HP Z6 G5 A:

  • Some of those lanes go directly to GPU slots (full x16).

  • Some are split to storage (NVMe drives), USB, network controllers, etc.

  • Some may be reserved internally and not exposed.

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🔹About "Virtual Lanes":

• "Virtual lanes" isn't an official PCIe standard term -it's marketing shorthand sometimes used.

• It can mean:

  • Dynamic assignment of physical PCIe lanes based on device presence.

  • SR-IOV (Single Root I/O Virtualization), where one physical device presents as multiple "virtual" devices.

• You don't gain more true bandwidth from "virtual lanes"; it’s about sharing or allocating existing real lanes cleverly.

• In your case (and for most GPU setups), you want real, physical PCIe lanes for maximum GPU performance.

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✅Short answer to your concern:

• You have plenty of real PCIe lanes.

• 2x RTX A5000 GPUs will each ideally get full x16 lanes if the motherboard allows (which HP usually designs for in high-end workstations like Z6 G5 A).

• You won't be "starved" for lanes.

• Other devices (such as SSDs, network cards) will also have more than enough bandwidth available.

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Summary:

CPU Spec                  What It Means

16 Cores / 32 Threads	CPU processing ability (how many tasks the CPU can handle simultaneously)
128 PCIe Gen 5 Lanes	High-speed data paths to GPUs, SSDs, and other expansion cards

You do not need to worry about your CPU threads limiting your GPU or PCIe bandwidth.

They are separate technologies -both are abundant in your system!

Kind Regards,

NonSequitur777