Tukukkk

I've recently been looking into getting a PCIe to SATA expansion card, which I think is otherwise known as a port multiplier (which was the first result in Google when I searched for such an adapter). I need one because I no longer have any free SATA ports on my system, but I'm confused about how exactly these cards work and how I can determine whether my PC will support them.

According to the above-linked Wikipedia page:

Many common controllers do not support this feature, as it is not a
requirement for a SATA controller.

Elsewhere I've seen it implied that this means support comes down to the motherboard, and whether the SATA controller on the motherboard supports such expansion cards.

However, port multipliers like the following work by connecting to the PCIe port directly - why then would the card be subject to the motherboard's own implementation of SATA? Am I fundamentally misunderstanding how this technology works?

If support for SATA port multipliers does boil down to the motherboard, how can I determine whether my motherboard supports them? My motherboard is an ASRock H61M-HVS and supports SATA 2.0 (3GB/s), but searching the manual for "multiplier" doesn't return any results.

I've recently been looking into getting a PCIe to SATA expansion card, otherwise known as a port multiplier, because I no longer have any free SATA ports on my system, but I'm confused about how exactly these cards work and how I can determine whether my PC will support them.

Your motherboard supports PCIe SATA expansion cards. Adding additional SATA ports, through an expansion card connected to a PCIe lane, only adds an additional SATA controller to the system. However, in order to boot from any disk connected to a PCIe SATA expansion card, it must specifically indicate that is supported.

I've recently been looking into getting a PCIe-SATA expansion card, otherwise known as a port multiplier because I no longer have any free SATA ports on my system, but I'm confused about how exactly these cards work and how I can determine whether my PC will support them.

PCIe-SATA is often referred to as SATA Express (SATAe), which of course, is an actual standard itself. Which should not be confused with eSATA, which is a different standard, to provide an interface for external SATA devices.

Elsewhere I've seen it implied that this means support comes down to the motherboard and whether the SATA controller on the motherboard supports such expansion cards.

Like other SATA features, like hot-swappable, support has to be supported by the SATA controller in addition to the device itself. PCIe SATA expansion cards have their own SATA controller and are not limited by the SATA controller on the motherboard itself.

However, port multipliers like the following work by connecting to the PCIe port directly - why then would the card be subject to the motherboard's own implementation of SATA? Am I fundamentally misunderstanding how this technology works?

Support would be subject to the expansion card's SATA controller, not the motherboard's SATA controller, any limitation of the motherboard's SATA controller would not be applicable to the expansion card.

If support for SATA port multipliers does boil down to the motherboard, how can I determine whether my motherboard supports them? My motherboard is an ASRock H61M-HVS and supports SATA 2.0 (3GB/s), but searching the manual for "multiplier" doesn't return any results.

The expansion card you linked to is NOT a SATA port multipler, it does not allow a single SATA port, to connect to multiple SATA devices. However, those devices do exist and would require SATA data (connected to the motherboard) and power cables (connected to the PSU) which allows you to connect 5 SATA devices to the card.

PCIe SATA expansion card does not necessarily mean Port Multiplier. To put it differently, a PCIe SATA expansion card is a PCIe card, that adds another (typically AHCI) host controller that provides SATA connectors, just like the AHCI controller on the mainboard. In the olden days, these were added to systems with only IDE controllers, and nowadays for devices that have too few SATA ports.

Port Multipliers are a totally different thing, you can think of them like USB hubs. One connector goes in, and many connectors go out. They all have to share the upstream bandwidth, while PCIe SATA expansion cards have the full bandwidth on each port.

Port Multipliers are not necessarily in the PCIe expansion form factor, but there are different models that fit in a 3.5″ slot. The ones that fit in a PCIe slot usually do only mechanically, as they will have not electrical contacts to the slot.

Since you say in your comment: "I'm looking for extra SATA ports because I've run out of them on my motherboard.":

One solution to this, would be to use a Sata Host Bus Adapter, which will expand your possible number of drives. There are many types of these, ranging from 2 ports upwards 16 on a single 8 lane card.