26 Years On — the Expansion Card Still Has New Tricks. Add the Functions You Want
What you want a machine to do keeps changing. Today it is a NAS, tomorrow a software router, the day after that a direct link to another machine for backups. In the past, every change meant another card, and a drawer slowly filled with cards you no longer used. PB65MX4 takes a different approach: don't change the card, change the module. What goes into those two front positions is up to you.
One Slot, Six Positions
Upstream is PCIe Gen4 x4 with 64 Gbps of total bandwidth, backward compatible with Gen3 / Gen2 / Gen1, and it fits x4, x8 and x16 slots. The card measures 180 × 69 mm.
64 Gbps is this card's master valve. Every port below draws from it. Keep that number in mind — the measurements that follow will make more sense.
The Two Front Positions: Functions You Decide
This is where the card differs most from an ordinary adapter.
The two front M.2 slots are not there for drives — they are there for modules. Four kinds of module turn the card into four different products:
With two positions, these are the combinations:
Run a NAS today with two SATA modules, switch to a software router tomorrow with two RJ45 modules — and the card stays in the slot.
Beyond these four, other M.2 peripheral modules can be fitted as well — that is what "customisable" means here.
The Two Rear M.2 Slots: Gen4 x4, No Compromise
When you need high-speed storage, use the rear. The two rear M.2 slots are PCIe 4.0 x4 and accept 2280 / 22110 drives.
Measured with AJA System Test (1920×1080 HD-1080i / 1 GB / 10-bit YUV):
Read speeds hold steadily at 5190–5261 MB/s, squarely inside the normal range for a PCIe 4.0 x4 SSD — the slot itself is not the bottleneck, and the drives run at full capability.
The division of labour is clear: modules at the front, SSDs at the rear. The x2 lanes at the front are ample for 10G networking and SATA; feeding a Gen4 SSD from them would be a waste.
"No Bifurcation" Saves You the Trip into BIOS
Plenty of people get tangled up in the phrase "no motherboard bifurcation required". The "split" here is not about opening the case — it means PCIe bifurcation.
An ordinary multi-port expansion card needs the motherboard to split one x16 link into several x4 links so that BIOS can hand them to different devices. If the board does not support it, the card is useless.
PB65MX4 does not need that. It carries its own B650 SouthBridge chipset, which acts as a PCIe switch: it occupies just one x4 link upstream and divides the downstream lanes itself. Whether the motherboard supports bifurcation is irrelevant, and there is nothing to configure in BIOS.
That means three kinds of machine can take it:
- Older motherboards — a PCIe 4.0 x4 slot is enough for full performance; Gen3 works too, at Gen3 speeds
- Branded pre-built systems — their BIOS is often locked and cannot be adjusted for bifurcation anyway
- Home-built NAS and software-router builds — no tuning during assembly; plug it in and you have six positions
Six Positions, All Tested
A card that claims many ports has to show how each one actually performs.
The two USB ports deserve a closer look: 1880 MB/s against 1000 MB/s — nearly double, matching the 20 Gbps / 10 Gbps spec ratio exactly. The bandwidth is genuinely there, with no contention between the two. Read and write are also nearly symmetrical (1880/1872, 1000/985), with no read-fast, write-slow imbalance.
This set is the clearest proof that the 64 Gbps upstream is sufficient. Two 10G ports at full speed add up to nearly 20 Gbit/s, about one third of the upstream link — which is why both ports really can run at full speed together, rather than looking good on paper and slowing down when used at once.
For anyone building a NAS, a software router or a multi-machine direct link, that matters more than any headline number.
Platforms
The same card was validated on three motherboards:
All three boards recognised the card with no configuration, which corroborates the earlier point: motherboard PCIe bifurcation support really is not required. Change platforms without changing the card.