GPUs · 2026-10-02
The 48 GB RTX 4090
NVIDIA never sold one. Who takes a 24 GB card to 48 GB, what it costs, what it breaks, and how to check a modified card before the money leaves your account.
A 48 GB RTX 4090 does not exist as a product. Every one of them was made by hand, by desoldering the GPU core and memory from a 24 GB card and rebuilding it on a board that can hold twice the memory. This page is about who does that work, what it costs, what it breaks, and how to check the card you receive.
Why it needs a custom board
The stock 4090 is not wired for clamshell memory. All its memory sits on one side of the PCB, so doubling capacity means either a custom PCB with twelve extra memory positions, or pairing the AD102 core with a 3090 Ti PCB that already has 24 memory module positions (Tom’s Hardware, VideoCardz).
It then needs a modified VBIOS, because stock firmware will not enumerate 48 GB, and usually a change to the memory-strap resistors so the card can address the denser packages (WCCFTech). One technician argues the 48 GB VBIOS must have been signed by NVIDIA, since the GPU’s Falcon chip verifies the checksum and an existing 4090 VBIOS cannot simply be edited.
The result reports 48 GB GDDR6X with roughly 900-937 GB/s of bandwidth on a 384-bit bus, 450 W TGP, and it runs on standard unmodified NVIDIA drivers (main-horse, gpulab.net, VideoCardz).
What it costs
| Route | Price | Source |
|---|---|---|
| Bare clamshell PCB kit, China | ~$142 | Tom’s Hardware |
| GDDR6X module, Chinese e-commerce | ~$24 each | same |
| Finished 48 GB 4090, China | ~$3,320-3,500 (24K RMB) | same, VideoCardz |
| US reseller, 48 GB blower card | $3,750-4,100 | MillionMiner |
| Labour only, send your own card (Dubai) | AED 1,500, memory/PCB/cooler extra | GPU Solutions |
| Reference point: RTX 6000 Ada 48 GB | $6,800 MSRP | Tom’s Hardware |
Prices move with memory-component availability: upgrades have been suspended outright when GDDR6X prices spiked (WindowsForum). Treat any figure as a snapshot and ask for a written quote.
Who does it
Tier 1 — verified on the shop’s own site, with a stated warranty. We checked these pages ourselves; the quote in each row comes from them.
| Shop | Where | What they do | Warranty |
|---|---|---|---|
| GPU Lab, LLC | United States (Central Michigan), ships worldwide, operating since 2021 | 4090 24→48 GB upgrade by mail-in or as a finished card, on 48 GB-capable PCBs, plus a custom water block and backplate for the modified board and general GPU repair. States IPC7095 Class 2 BGA rework certification, multi-zone rework stations with infrared preheat to 450 °C and a memory-test fixture for every module pulled from a donor. Says its boards use full-spec AD102-300-A1 cores and the NVIDIA PG139 reference layout rather than the AD102-250-A1 of China-market 4090-D cards. | 90-day standard warranty on cards and on the upgrade service, extended options; 30-day return on unopened items. Quotes 48-hour burn-in with gpu-burn plus ComfyUI Wan 2.2 loops, and ships a full diagnostic report. |
| GPU Solutions FZ-LLC | United Arab Emirates (Dubai) | 4090 24→48 GB: replacement PCB with expanded memory positions, twelve additional Micron GDDR6X modules, custom BIOS. Also doubles a 2080 Ti 11→22 GB and other cards. | 90-day warranty stated on the upgrade service; notes that a custom BIOS can change or remove vendor features such as RGB, fan curves and monitoring. |
Tier 2 — reported by the press or by the community, not verified by us on a shop page. These may be entirely legitimate; we simply have not confirmed them first-hand, so treat the details as claims.
| Name | Where | What is reported | Source |
|---|---|---|---|
| AiGPU | Japan | 2080 Ti 11→22 GB for ¥45,000 (~$282) when you supply the card; lists A2000 6→12, 3070 8→16, 3080 10→20, 4080/4080 Super 16→32 and 4090 24→48 GB | VideoCardz |
| customgpu_official | United States (Palo Alto, CA) | Sold modified 2080 Ti 22 GB cards on eBay, e.g. $499 for an MSI Aero | Tom’s Hardware |
| Zhang Ge (“Brother Zhang”) | China | Hand-builds 48 GB 4090 cards and repairs GPUs, sometimes around $140 a repair | HARDForum |
| “Aisawk” on Goofish/Xianyu | China | 2080 Ti 22 GB cards and a $120 mail-in upgrade, reported to use original Samsung GDDR6 and ALPHA OM-367 solder paste | Tom’s Hardware |
| MillionMiner | Reseller, contact lines in the US, Germany and UAE | Sells finished 48 GB blower cards with modified firmware; states there is no NVIDIA warranty | MillionMiner |
Most of the market runs through Taobao, JD, Goofish/Xianyu and cross-border AliExpress listings rather than branded retail: a single Taobao keyword page showed roughly 5,000 items including nationwide mail-in “change the VRAM” services from ¥100, and AliExpress has a wholesale category for “RTX 4090 48GB” (Taobao, AliExpress). Cheap and unaccountable go together there. If a shop cannot show you a real address, a certification, a warranty term in writing and a diagnostic report, it is not a shop, it is a listing.
What goes wrong
- Intermittent failures. A card can pass a short benchmark and fail hours into a CUDA load. One analysis puts the success rate below 15% without professional BGA equipment, and notes that a larger memory package can fit the footprint yet fail memory training or corrupt data at 19.5 Gbps (LaptopJudge).
- Bare-board scams. Buyers of second-hand “48 GB 4090” cards have received boards and coolers with neither the GPU nor the memory fitted (VideoCardz).
- Unknown provenance. The card may not have been new when it was modified, there is no NVIDIA warranty, and firmware support depends entirely on whoever made it.
- Feature loss. A custom BIOS and an aftermarket cooler can mean no vendor RGB, different fan curves and missing monitoring.
- Repair refusal. A card already modified may be rejected for warranty service by the original vendor.
- Renamed silicon. Verify what you actually got with a compute benchmark, not the label.
Check it before you pay
nvidia-smimust report about 49,152 MiB of memory, not 24,576 MiB.- Run
memtest_vulkanplus a long burn-in (gpu-burn, Furmark, 3DMark) — hours, not minutes, because these faults surface late (memtest_vulkan). - Run a memory-heavy FP8 or PyTorch benchmark and compare it against a stock 24 GB card of the same model, which catches a renamed or slower GPU (main-horse).
- For a 48 GB 3090, the community validator (GPU name, ~49,152 MiB, torch sees the memory, compute capability, a write test to 92% of capacity, VBIOS/driver/power/temperature, plus Xid/WHEA/PCIe error logs) is a good model for what to insist on checking on any of these cards (validator).
- Confirm it boots on standard, unmodified NVIDIA drivers, with no Xid, WHEA or PCIe errors in the OS log during the burn-in.
- Ask which VBIOS is flashed, ask for the post-mod diagnostic report, and get the warranty term in writing. Ninety days is the current norm among the shops that publish one; thirty days exists too.
The simpler alternative
If you are weighing this against an RTX 6000 Ada, an RTX PRO 6000 Blackwell, or simply two 24 GB cards, put the numbers side by side on GPUs and check what actually fits on Will it fit?. A modified card buys you capacity per dollar and costs you warranty, resale value and firmware independence. That trade is worth it for some people and not for others — but make it deliberately.
Spotted a shop that deserves to be here, or one that should not be? Send it to the address on Submit. This page is re-checked, and every entry is verified against the shop’s own pages.