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ASRock B850 Pro-A
ASRock B850M Pro RS

ASRock B850 Pro-A ASRock B850M Pro RS

Overview

When comparing the ASRock B850 Pro-A and the ASRock B850M Pro RS, both boards share a strong AM5 and B850 chipset foundation with DDR5 memory support, yet they diverge in meaningful ways across form factor, expansion slots, storage capacity, and port configurations. This comparison breaks down exactly where each board pulls ahead, helping you make a well-informed decision for your next build.

Common Features

  • ✓ Both boards use the AM5 CPU socket.
  • ✓ Both boards feature the B850 chipset.
  • ✓ Wi-Fi is not available on either product.
  • ✓ Bluetooth is not available on either product.
  • ✓ Both boards support HDMI 2.1.
  • ✓ Both boards are easy to overclock.
  • ✓ RGB lighting is present on both boards.
  • ✓ Easy BIOS reset is not available on either product.
  • ✓ Both boards support a maximum memory amount of 256GB.
  • ✓ Both boards support overclocked RAM speeds of up to 8000 MHz.
  • ✓ Both boards have 4 memory slots and 2 memory channels.
  • ✓ Both boards use DDR5 memory.
  • ✓ ECC memory support is not available on either product.
  • ✓ Both boards have 1 USB 3.2 Gen 2 USB-C port.
  • ✓ Both boards have 1 RJ45 port.
  • ✓ USB 3.2 Gen 2x2, USB 4, and Thunderbolt ports are not available on either product.
  • ✓ Both boards have 4 SATA 3 connectors and no SATA 2 connectors.
  • ✓ A TPM connector is present on both boards.
  • ✓ Both boards offer 1 PCIe 5.0 x16 slot.
  • ✓ Both boards support 7.1 audio channels with 3 audio connectors.
  • ✓ Both boards support RAID 0, RAID 1, and RAID 10, but neither supports RAID 5 or RAID 0+1.
  • ✓ An S/PDIF Out port is not available on either product.

Main Differences

  • • The form factor is ATX on the ASRock B850 Pro-A and Micro-ATX on the ASRock B850M Pro RS.
  • • The board width is 305 mm on the ASRock B850 Pro-A and 244 mm on the ASRock B850M Pro RS.
  • • USB 3.2 Gen 2 USB-A ports number 0 on the ASRock B850 Pro-A and 1 on the ASRock B850M Pro RS.
  • • USB 3.2 Gen 1 USB-A ports number 4 on the ASRock B850 Pro-A and 2 on the ASRock B850M Pro RS.
  • • A USB 3.2 Gen 1 USB-C port is present on the ASRock B850 Pro-A but not available on the ASRock B850M Pro RS.
  • • USB 2.0 ports number 6 on the ASRock B850 Pro-A and 4 on the ASRock B850M Pro RS.
  • • A DisplayPort output is present on the ASRock B850M Pro RS but not available on the ASRock B850 Pro-A.
  • • USB 3.2 Gen 1 ports through expansion number 2 on the ASRock B850 Pro-A and 4 on the ASRock B850M Pro RS.
  • • USB 2.0 ports through expansion number 3 on the ASRock B850 Pro-A and 4 on the ASRock B850M Pro RS.
  • • USB 3.0 ports through expansion number 2 on the ASRock B850 Pro-A and 4 on the ASRock B850M Pro RS.
  • • Fan headers number 7 on the ASRock B850 Pro-A and 5 on the ASRock B850M Pro RS.
  • • M.2 sockets number 4 on the ASRock B850 Pro-A and 3 on the ASRock B850M Pro RS.
  • • A PCIe 4.0 x16 slot is present on the ASRock B850 Pro-A but not available on the ASRock B850M Pro RS.
  • • A PCIe x4 slot is present on the ASRock B850M Pro RS but not available on the ASRock B850 Pro-A.
Specs Comparison
ASRock B850 Pro-A

ASRock B850 Pro-A

ASRock B850M Pro RS

ASRock B850M Pro RS

General info:
CPU socket AM5 AM5
chipset B850 B850
form factor ATX Micro-ATX
release date January 2025 January 2025
supports Wi-Fi ✕ ✕
Has Bluetooth ✕ ✕
HDMI version HDMI 2.1 HDMI 2.1
Easy to overclock ✓ ✓
has RGB lighting ✓ ✓
Easy to reset BIOS ✕ ✕
Has dual BIOS ✓ ✓
CPU sockets 1 1
Has integrated graphics ✕ ✕
warranty period 3 years 3 years
height 244 mm 244 mm
width 305 mm 244 mm
Has integrated CPU ✕ ✕

Both the ASRock B850 Pro-A and the ASRock B850M Pro RS share the same foundational platform: the AM5 socket with a B850 chipset, identical HDMI 2.1 output, dual BIOS protection, RGB lighting, and a 3-year warranty. Neither board includes integrated Wi-Fi, Bluetooth, or an integrated CPU, so users on both will need to factor in a discrete GPU and, if needed, a wireless adapter.

The single meaningful differentiator in this group is form factor. The Pro-A is a full ATX board measuring 305 × 244 mm, while the Pro RS is Micro-ATX at 244 × 244 mm — roughly 20% smaller in footprint. In practice, this means the Pro RS fits into more compact cases and is a stronger candidate for space-constrained builds, while the Pro-A's larger PCB typically allows for more expansion slots, better component spacing, and improved airflow routing in mid-tower or full-tower enclosures.

For users prioritizing a compact, tidy build without sacrificing the B850 platform's capabilities, the Pro RS holds the edge in this group thanks to its smaller footprint. However, builders who want maximum expandability or are working with a spacious case will find the Pro-A's ATX layout more accommodating. All other general characteristics being equal, the choice here comes down entirely to case compatibility and build size preference.

Memory:
maximum memory amount 256GB 256GB
overclocked RAM speed 8000 MHz 8000 MHz
memory slots 4 4
DDR memory version 5 5
memory channels 2 2
Supports ECC memory ✕ ✕

Both the ASRock B850 Pro-A and the ASRock B850M Pro RS support a maximum memory capacity of 256GB. They both also offer the same overclocked RAM speed of 8000 MHz, and each has 4 memory slots. The DDR memory version is 5 for both products, and they both operate with 2 memory channels.

Neither motherboard supports ECC memory, as indicated in the specifications for both models.

Ports:
USB 3.2 Gen 2 ports (USB-A) 0 1
USB 3.2 Gen 1 ports (USB-A) 4 2
USB 3.2 Gen 2 ports (USB-C) 1 1
USB 3.2 Gen 1 ports (USB-C) 1 0
USB 2.0 ports 6 4
USB 3.2 Gen 2x2 ports 0 0
USB 4 40Gbps ports 0 0
USB 4 20Gbps ports 0 0
Thunderbolt 4 ports 0 0
Thunderbolt 3 ports 0 0
has an HDMI output ✓ ✓
DisplayPort outputs 0 1
RJ45 ports 1 1
Has USB Type-C ✓ ✓
eSATA ports 0 0
DVI outputs 0 0
has a VGA connector ✕ ✕
PS/2 ports 0 0

The ASRock B850 Pro-A and the ASRock B850M Pro RS offer a similar range of ports, but with some differences in USB configurations. The B850 Pro-A has 4 USB 3.2 Gen 1 USB-A ports, 1 USB 3.2 Gen 2 USB-C port, and 1 USB 3.2 Gen 1 USB-C port. In contrast, the B850M Pro RS has 1 USB 3.2 Gen 2 USB-A port, 2 USB 3.2 Gen 1 USB-A ports, and no USB 3.2 Gen 1 USB-C ports. Both motherboards offer 6 USB 2.0 ports. Neither motherboard features USB 3.2 Gen 2x2, USB 4 40Gbps, USB 4 20Gbps, Thunderbolt 4, or Thunderbolt 3 ports.

Both boards include an HDMI output, but only the B850M Pro RS offers a DisplayPort output, while the B850 Pro-A does not. Both motherboards have 1 RJ45 port for network connectivity. In terms of USB Type-C, both products support it, but with different configurations. The B850 Pro-A has both a USB 3.2 Gen 2 USB-C port and a USB 3.2 Gen 1 USB-C port, while the B850M Pro RS only has a USB 3.2 Gen 2 USB-C port.

Neither motherboard has eSATA ports, DVI outputs, a VGA connector, or PS/2 ports.

Connectors:
USB 3.2 Gen 1 ports (through expansion) 2 4
USB 2.0 ports (through expansion) 3 4
SATA 3 connectors 4 4
fan headers 7 5
USB 3.0 ports (through expansion) 2 4
M.2 sockets 4 3
Has TPM connector ✓ ✓
U.2 sockets 0 0
Has mSATA connector ✕ ✕
SATA 2 connectors 0 0

The ASRock B850 Pro-A and the ASRock B850M Pro RS both offer similar connectors in many areas, but there are a few key differences. Both motherboards feature 4 SATA 3 connectors. The B850 Pro-A provides 2 USB 3.2 Gen 1 ports and 3 USB 2.0 ports through expansion, while the B850M Pro RS offers 4 USB 3.2 Gen 1 ports and 4 USB 2.0 ports through expansion. The B850 Pro-A has 2 USB 3.0 ports through expansion, whereas the B850M Pro RS offers 4 USB 3.0 ports through expansion.

In terms of fan headers, the B850 Pro-A includes 7 fan headers, while the B850M Pro RS has 5 fan headers. The number of M.2 sockets differs between the two, with the B850 Pro-A supporting 4 M.2 sockets and the B850M Pro RS supporting 3 M.2 sockets. Both motherboards have a TPM connector and do not include any U.2 or mSATA connectors. Neither motherboard has SATA 2 connectors.

Expansion slots:
PCIe 4.0 x16 slots 1 0
PCIe 5.0 x16 slots 1 1
PCIe 3.0 x16 slots 0 0
PCIe x1 slots 0 0
PCI slots 0 0
PCIe 2.0 x16 slots 0 0
PCIe x4 slots 0 1
PCIe x8 slots 0 0

The ASRock B850 Pro-A and the ASRock B850M Pro RS differ in their expansion slot configurations. The B850 Pro-A has one PCIe 4.0 x16 slot and one PCIe 5.0 x16 slot, while the B850M Pro RS has one PCIe 5.0 x16 slot but no PCIe 4.0 x16 slot. The B850M Pro RS includes a PCIe x4 slot, which the B850 Pro-A does not have. Neither motherboard includes PCIe 3.0 x16, PCI, PCIe 2.0 x16, or PCIe x1 slots.

In summary, the B850 Pro-A offers PCIe 4.0 x16 and PCIe 5.0 x16 slots, whereas the B850M Pro RS offers a PCIe 5.0 x16 slot and a PCIe x4 slot. Both motherboards lack PCIe x1, PCI, PCIe 2.0 x16, and PCIe 3.0 x16 slots.

Audio:
audio channels 7.1 7.1
Has S/PDIF Out port ✕ ✕
audio connectors 3 3

Both the ASRock B850 Pro-A and the ASRock B850M Pro RS support 7.1 audio channels, providing similar audio capabilities. Neither motherboard includes an S/PDIF Out port. Both products offer 3 audio connectors for sound output.

Overall, the audio specifications are identical between the two models, with the same channel support, lack of S/PDIF Out, and the same number of audio connectors.

Storage:
Supports RAID 1 ✓ ✓
Supports RAID 10 (1+0) ✓ ✓
Supports RAID 5 ✕ ✕
Supports RAID 0 ✓ ✓
Supports RAID 0+1 ✕ ✕

Both the ASRock B850 Pro-A and the ASRock B850M Pro RS support RAID 1, RAID 10 (1+0), and RAID 0 configurations, allowing users to set up various RAID arrays for redundancy or performance. Neither motherboard supports RAID 5 or RAID 0+1.

These storage capabilities are identical between the two models, with both offering the same RAID options and lacking support for RAID 5 and RAID 0+1.

Comparison Summary & Verdict

Both the ASRock B850 Pro-A and the ASRock B850M Pro RS are well-matched at their core, sharing the AM5 socket, B850 chipset, DDR5 support across four slots, and a single PCIe 5.0 x16 slot. Yet the details tell two different stories. The ASRock B850 Pro-A is the stronger pick for enthusiasts who need maximum expandability: its ATX layout accommodates four M.2 sockets, seven fan headers, a PCIe 4.0 x16 slot, and a wider USB port selection. Meanwhile, the ASRock B850M Pro RS is the better fit for compact builds, offering a Micro-ATX footprint, a built-in DisplayPort output, and more internal USB expansion headers ideal for smaller chassis with tight integration needs.

ASRock B850 Pro-A
Buy ASRock B850 Pro-A if...

Buy the ASRock B850 Pro-A if you want a full-size ATX board with four M.2 sockets, seven fan headers, and a PCIe 4.0 x16 slot for a heavily expanded, well-cooled desktop build.

ASRock B850M Pro RS
Buy ASRock B850M Pro RS if...

Buy the ASRock B850M Pro RS if you are building a compact Micro-ATX system and value a built-in DisplayPort output alongside solid internal USB expansion support.