AMD Chipset Specifications Compared: AM4 300/400/500 and AM5 600/800 Series

AMD desktop chipsets cannot be ranked solely by the letters X, B, and A.

Although B350, B550, B650, and B850 all belong to the B tier, they use different sockets and I/O generations. Likewise, a PCIe 4.0 label must be interpreted carefully: it may refer only to CPU-direct lanes rather than chipset-provided lanes.

The specifications that actually determine a motherboard’s connectivity include:

1. The generation and bifurcation options of CPU-direct graphics lanes;
2. CPU-direct NVMe lanes;
3. The uplink between the CPU and chipset;
4. General-purpose PCIe lanes supplied by the chipset;
5. Lane sharing between PCIe and SATA;
6. The number of USB 20Gbps, 10Gbps, 5Gbps, and USB4 ports;
7. CPU and memory overclocking support;
8. The lane layout implemented by the motherboard vendor.

This article compares the AM4 300, 400, and 500 series and the AM5 600 and 800 series from a specification perspective.

Understand the Three PCIe Lane Counts First

The most commonly confused figures in chipset specifications are total lanes, usable lanes, and chipset lanes.

CPU-Direct Lanes

CPU-direct lanes bypass the chipset. They are normally assigned to the graphics slot, the first M.2 NVMe drive, and the CPU-to-chipset connection.

A typical AM4 Ryzen desktop processor can be simplified as follows:

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Ryzen CPU
  ├── PCIe x16：显卡
  ├── PCIe x4：NVMe
  └── PCIe x4：连接芯片组

Some APUs, Athlon processors, and OEM processors expose fewer or slower lanes, so this typical desktop Ryzen layout does not apply to every AM4 CPU.

Chipset Downstream Lanes

The chipset connects to the CPU through one uplink and supplies additional PCIe, SATA, and USB connectivity.

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CPU
 │ 芯片组上行
 ▼
芯片组
 ├── PCIe x4 / x2 / x1
 ├── SATA
 ├── USB
 ├── 网卡
 └── 其他板载控制器

All chipset-connected devices share the uplink, so several interfaces under simultaneous load compete for bandwidth.

Total and Usable Platform Lanes

AMD’s official PCIe Lanes (Total/Usable) figures describe the whole platform. They count both CPU and chipset resources, then subtract lanes that cannot be assigned directly to peripherals.

For example, B550’s 38/30 figure does not mean that the B550 silicon itself supplies 30 PCIe lanes.

A motherboard also consumes lanes for Ethernet, Wi-Fi, audio, and auxiliary controllers, so fewer lanes usually appear as user-accessible slots.

AMD Chipset Generation Overview

The maximum generation still depends on the installed CPU. The chipset-side generation also does not mean that every slot on a motherboard runs at that speed.

AM4 300 Series: X370, B350, and A320

The 300 series launched with first-generation Ryzen and uses the original Promontory architecture.

• X370 targets high-end systems and supports graphics-lane bifurcation;
• B350 targets mainstream systems and supports CPU overclocking;
• A320 targets entry-level systems and does not support CPU overclocking.

Official Platform Specifications

The maximum SATA figure is a platform limit that includes processor-provided resources; it is not the number of fixed SATA ports supplied by the chipset alone.

X370 Lane Characteristics

X370 allows the CPU graphics lanes to operate as 2×8, which is why early dual-GPU boards were concentrated in this tier.

Its general-purpose chipset lanes are primarily PCIe 2.0. Even when the graphics slot and first NVMe drive use PCIe 3.0, a second M.2 slot or x1 slot may still be limited to Gen2.

Common sharing arrangements include:

• A second full-length slot consuming CPU graphics lanes;
• A chipset-connected M.2 slot sharing lanes with SATA ports;
• x1 slots sharing resources with onboard controllers;
• One or two SATA ports being disabled when a particular M.2 slot is populated.

B350 Versus A320

B350 retains CPU overclocking and provides more usable platform lanes than A320.

A320 lacks CPU overclocking and 2×8 graphics bifurcation, and it offers fewer USB 10Gbps ports and usable PCIe lanes.

A320 may be sufficient for one graphics card, one NVMe drive, and a few SATA devices. B350 gives vendors more flexibility when adding a second SSD or more onboard controllers.

AM4 400 Series: X470 and B450

X470 and B450 still use a PCIe 3.0 x4 chipset uplink, while their general-purpose chipset lanes remain primarily PCIe 2.0.

Their improvements are more about platform maturity, firmware, memory compatibility, and feature updates than a major increase in I/O.

Official Platform Specifications

Choosing Between X470 and B450

X470 supports 2×8 CPU graphics lanes and has higher usable-lane and SATA limits. It better accommodates layouts with two full-length slots, two M.2 sockets, and more onboard controllers.

B450 retains CPU and memory overclocking at a lower platform cost. It is usually sufficient for one graphics card, one CPU-direct NVMe drive, one chipset-connected M.2 drive, and four to six SATA devices.

Their shared limitation is chipset-side Gen2. A second M.2 drive, 2.5GbE controller, extra USB controller, and x1 slots must compete for limited chipset bandwidth.

AM4 500 Series: X570, B550, and A520

The 500 series is not simply three high-, middle-, and low-end tiers. It contains three distinct PCIe arrangements.

Official Platform Specifications

These figures must be interpreted together with the processor. An APU may expose different PCIe generations or lane configurations from a standard Ryzen desktop CPU.

X570: Gen4 on the Chipset Side Too

X570 uses a PCIe 4.0 x4 chipset uplink and can also supply PCIe 4.0 downstream resources.

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Ryzen CPU
  ├── PCIe 4.0 x16：显卡
  ├── PCIe 4.0 x4：第一块 NVMe
  └── PCIe 4.0 x4：X570
                         ├── PCIe 4.0 设备
                         ├── SATA
                         └── USB

The X570 platform provides 44/36 total/usable lanes, supports up to 14 SATA ports, and has the highest high-speed USB limit in the AM4 family.

The tradeoff is higher chipset power and cooling demand. Early boards commonly used chipset fans, while more X570S products use passive cooling.

B550: CPU Gen4, Chipset Gen3

Not every B550 interface supports PCIe 4.0.

• A compatible CPU’s x16 graphics link can run at Gen4;
• The CPU-direct x4 NVMe link can run at Gen4;
• The CPU-to-B550 uplink is Gen3 x4;
• B550 downstream lanes are primarily Gen3.

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Ryzen CPU
  ├── PCIe 4.0 x16：显卡
  ├── PCIe 4.0 x4：M.2_1
  └── PCIe 3.0 x4：B550
                         ├── PCIe 3.0 M.2_2
                         ├── PCIe x1
                         ├── SATA
                         └── USB

B550 provides 38/30 total/usable lanes, supports up to eight SATA ports, allows 2×8 graphics bifurcation, and supports CPU overclocking.

It lacks X570’s Gen4 chipset lanes, but usually has lower power, cost, and cooling requirements.

A520: An All-Gen3 Platform

A520 limits the platform to PCIe 3.0, does not offer 2×8 graphics bifurcation, and does not support CPU overclocking.

It provides 34/26 total/usable PCIe lanes, up to six SATA ports, 13 USB ports, and up to five USB 10Gbps ports.

The CPU-direct NVMe link can still run at PCIe 3.0 x4, and the chipset side is faster than the Gen2 GPP lanes found on the 300 and 400 series.

What it mainly lacks is Gen4, CPU overclocking, 2×8 bifurcation, and additional I/O.

B550A Is Not the Same as Retail B550

B550A is not merely a renamed retail B550.

AMD lists B550A as a PCIe 3.0 platform with 40/32 total/usable lanes and up to 10 SATA ports. Its positioning is closer to the OEM Promontory-LP platform.

Consequently, a branded PC labeled B550A should not automatically be assigned retail B550’s CPU-direct Gen4 capabilities.

Commercial models such as PRO 500, PRO 560, and PRO 565 also have their own USB, SATA, overclocking, and CPU-support limits. Always verify the full chipset name.

AM5 600-Series Specifications

AM5 moves to DDR5 and introduces CPU-direct PCIe 5.0. The E suffix indicates more comprehensive Gen5 requirements.

The Gen5 count is the platform’s maximum capability. It does not mean that every motherboard exposes every lane as a user-accessible slot.

X670E and X670

Both offer 44 usable lanes and up to eight configurable SATA/PCIe 3.0 ports.

X670E requires Gen5 graphics and Gen5 NVMe and supports up to 24 Gen5 lanes. X670 requires only Gen4 graphics and supports up to eight Gen5 lanes.

The X670 family usually cascades two PROM21 chips to supply more I/O:

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CPU
 │ PCIe 4.0 x4
 ▼
PROM21 #1
 ├── PCIe / SATA / USB
 └── PCIe 4.0 x4
          ▼
       PROM21 #2
          └── 更多 PCIe / SATA / USB

Devices behind the second chipset reach the CPU through the first chipset, so vendors generally place latency- and bandwidth-sensitive devices on CPU-direct lanes or the first chipset.

B650E and B650

Both support CPU and memory overclocking and provide 36 usable lanes.

B650E requires Gen5 graphics and NVMe and supports up to 24 Gen5 lanes. B650 uses Gen4 graphics, while implementation of a Gen5 NVMe slot is optional.

AMD’s table lists zero guaranteed Gen5 lanes for B650. This means the platform specification does not require Gen5; it does not mean that every B650 motherboard lacks a Gen5 M.2 slot.

A620

A620 provides Gen4 x16 graphics and Gen4 x4 NVMe. It does not support CPU overclocking, but it does support DDR5 memory overclocking and EXPO.

Compared with B650, it has fewer lanes, fewer USB 10Gbps ports, no USB 20Gbps, and less lane-bifurcation flexibility.

AM5 800-Series Specifications

The 800 series continues to use AM5 and DDR5 while redefining the Gen5, USB4, and overclocking tiers.

X870E and X870

X870E retains 44 usable lanes, up to 24 Gen5 lanes, and eight configurable SATA/PCIe 3.0 ports.

X870 provides 36 usable lanes and up to four configurable SATA/PCIe 3.0 ports, while still requiring Gen5 graphics and NVMe.

Both require USB4 as standard, one of their clearest specification changes from the 600 series.

A USB4 controller consumes PCIe and display resources, so a motherboard may adjust M.2 availability, graphics bifurcation, or other slots accordingly.

B850 and B840

B850 retains CPU and memory overclocking, uses Gen4 graphics lanes, and supplies Gen5 x4 for NVMe, for a platform maximum of four Gen5 lanes.

B840 does not support CPU overclocking, only memory overclocking. Its graphics and NVMe links are primarily Gen4, with no Gen5 requirement.

B850 also has higher USB 20Gbps and 10Gbps limits. USB4 is optional on both models and is not guaranteed by the chipset name.

X, B, and A Tiers Cannot Be Compared Directly Across Generations

The letters indicate positioning only within the same generation.

X570 Versus X670/X870

X570 belongs to AM4 and DDR4, but its chipset-side PCIe 4.0 resources remain strong.

X670 and X870 move to AM5 and DDR5 and introduce CPU-direct Gen5 and newer USB requirements.

X570 is not inherently behind when only chipset-side Gen4 is considered. AM5 is more complete when CPU Gen5, DDR5, and future processor support matter.

B550 Versus B650/B850

B550 combines CPU-direct Gen4 with a Gen3 chipset.

B650 and B850 move to AM5 and offer Gen4 chipset I/O. Gen5 NVMe is optional on B650, while B850 explicitly provides a Gen5 x4 NVMe link.

A520 Versus A620/B840

A520 is an AM4 Gen3 platform. A620 and B840 belong to AM5, bring graphics and NVMe to at least Gen4, and support DDR5 memory overclocking.

All three omit CPU overclocking, but their I/O generations are very different.

Why the SATA Count Often Differs on Finished Motherboards

AMD specifies a platform maximum or a configurable SATA (or PCIe 3.0) count.

A motherboard may expose fewer ports because:

• CPU SATA/PCIe resources are assigned to M.2;
• Combo lanes are configured as PCIe;
• An M.2 socket shares lanes with two SATA ports;
• Lanes are consumed by Ethernet, Wi-Fi, or extra USB;
• Board size and cost impose limits;
• Some AM5 lanes can operate as SATA or PCIe 3.0, but not both.

Motherboard manuals commonly include notices such as:

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M.2_2 occupied: SATA_5 and SATA_6 disabled
PCIEX4 operates at x2 when M.2_3 is installed
SATA mode and PCIe mode are mutually exclusive

These are consequences of lane sharing, not firmware faults.

USB Specifications Must Be Separated by Speed

“14 USB ports” does not indicate how many are high-speed ports.

Count USB 2.0, 5Gbps, 10Gbps, 20Gbps, and USB4 separately.

Type-C describes only the connector. The port may run at 5Gbps, 10Gbps, 20Gbps, or USB4 and may not support display output or USB PD.

Compare the speed of every physical port rather than merely counting Type-A and Type-C connectors.

Separate CPU and Memory Overclocking

Chipset-level overclocking support does not guarantee that a motherboard’s power delivery is suitable for a high-power CPU.

Also inspect the VRM, cooling, firmware power limits, CPU support list, and memory QVL.

What 1×16 and 2×8 Actually Mean

1×16/2×8 means that the CPU graphics lanes support bifurcation. It does not guarantee two electrically x8 slots on every motherboard.

The board still needs the appropriate routing, firmware configuration, and CPU.

Many second mechanical x16 slots are electrically only chipset x4. Look for wording such as x16 physical, x4 electrical or PCIEX16_2 runs at x4.

Choose by Workload

One Graphics Card and One NVMe Drive

AM4 options such as B450, B550, and A520 and AM5 options such as A620, B650, B840, and B850 usually cover this configuration.

Prioritize CPU compatibility, first-M.2 generation, VRM quality, and required USB connectivity instead of automatically paying for an X-series chipset.

Two or Three High-Speed NVMe Drives

Check:

• How many M.2 sockets are CPU-direct;
• Whether the chipset uplink is Gen3 x4 or Gen4 x4;
• The lane count and generation of additional M.2 sockets;
• Sharing between M.2, SATA, and PCIe slots;
• Whether simultaneous drive activity shares the chipset uplink.

X570 is advantageous on AM4. On AM5, B650/B850 and higher tiers generally make multiple high-speed M.2 sockets easier to implement.

Many SATA Devices

Platform limits provide an initial filter:

• X370/X470: up to 10;
• X570: up to 14;
• B550: up to 8;
• X670E/X670/X870E: up to 8 configurable SATA or PCIe 3.0 ports;
• B650/B850/X870/A620/B840: generally up to 4 configurable ports.

Finished boards often expose fewer. Above six to eight SATA ports, verify whether the board uses a third-party controller.

USB4

X870E and X870 require USB4 as standard.

On B850, B840, and the 600 series, USB4 depends on the motherboard design and cannot be inferred from the chipset name alone.

CPU Overclocking

Avoid A320, A520, A620, and B840. Also inspect motherboard power delivery instead of looking only for PBO or multiplier settings in firmware.

Common Specification Misreadings

Treating Every B550 Interface as Gen4

B550’s Gen4 connectivity mainly comes from a compatible CPU’s graphics and NVMe lanes. Its chipset uplink and downstream lanes are primarily Gen3.

Treating Usable Platform Lanes as Chipset Lanes

Figures such as 38/30, 44/36, and 36/24 include CPU resources and cannot be used directly to calculate chipset ports.

Assuming X870 Has More of Every I/O Than X670E

X670E offers 44 usable lanes and up to eight configurable SATA/PCIe 3.0 ports; X870 offers 36 and up to four.

X870 requires USB4, but its overall I/O count is not necessarily higher than X670E’s.

Assuming B650 Can Never Have a Gen5 M.2 Slot

B650 does not require Gen5, but vendors may implement a Gen5 CPU-direct NVMe link. Check the specific motherboard.

Assuming Entry-Level AM5 Chipsets Cannot Overclock Memory

A620 and B840 support DDR5 memory overclocking; they omit CPU overclocking.

Ignoring Processor-Specific Differences

Installing an APU on the same motherboard may change the graphics-link generation, NVMe generation, or available lane count.

The final decision must use the exact CPU and motherboard combination.

Summary

AMD chipset generations can be summarized as follows:

1. AM4 300/400-series CPUs provide Gen3 direct lanes, while chipset downstream lanes are primarily Gen2;
2. X570 raises both the chipset uplink and downstream resources to Gen4;
3. B550 combines CPU-direct Gen4 with a Gen3 chipset;
4. A520 retains Gen3 but reduces lanes, overclocking, and bifurcation features;
5. The AM5 600 series introduces DDR5, CPU-direct Gen5, and PROM21;
6. The AM5 800 series redefines Gen5 and USB4 requirements;
7. X, B, and A indicate tiers only within a generation, so cross-generation comparisons must return to PCIe, SATA, USB, and overclocking specifications.

When choosing a motherboard, identify CPU-direct graphics and NVMe first, then examine the chipset uplink, and finally verify sharing among M.2, SATA, USB, and full-length slots.

This prevents headline figures such as “total lanes,” “Gen5 Ready,” or a mechanical x16 slot from becoming misleading.

References

• AMD Socket AM4 Chipset Specifications and CPU Compatibility
• AMD Socket AM5 Chipset Specifications
• AMD Socket AM5 Quick Reference Guide