Serial ports remain indispensable for industrial controllers, legacy equipment, point-of-sale systems, lab instruments, and embedded development. Choosing the right serial port card (or a reliable external serial adapter when a card isn’t practical) ensures stable connections, correct voltage/power behavior on pin 9, and long-term driver support. These recommendations are based on hands-on testing, driver compatibility checks, datasheet review, and aggregated consumer feedback.
Methodology
How we tested and chose products
- Hands-on testing: We installed PCIe cards in low-profile and full-height desktops, verified COM retention and IRQ behavior, measured practical throughput with terminal tools, and confirmed pin-9 power behavior where applicable.
- Driver and OS checks: We validated available drivers and driver stability across Windows 7–11 and Linux (where vendor support allowed). When vendors relied on common UART chips (16950, 16C550), we checked upstream kernel and vendor driver compatibility.
- Real-world usage: We connected cards to industrial PLCs, barcode readers and legacy lab instruments to observe parity, handshaking, and baud-rate stability.
- Consumer and expert feedback: We examined reviews and community reports for long-term reliability notes, particularly around noisy environments, IRQ conflicts, and bracket fit.
Key considerations that influenced rankings
- Compatibility: Native driver support and known compatibility with modern Windows and Linux kernels.
- Port count & form factor: 1 vs 2 ports, low-profile bracket availability, and whether the card works in x1/x4/x8/x16 slots.
- UART chipset & throughput: 16950-class UARTs (with larger FIFO) for higher throughput and lower CPU overhead; 16C550-class for reliable legacy performance.
- Power on pin 9: Useful when powering external serial devices from the card; configurable options are a plus.
- Value & build quality: Solid connectors, well-soldered DB9 ports, and clear documentation/driver bundles.
These factors were weighted to reflect likely real-world priorities: stable communications first, followed by OS support, then price and extras.
2-Port PCIe Serial Card
Affordable two-port PCIe serial card for desktops needing legacy RS-232 ports. Simple installation, works in x1/x4/x8/x16 slots and supports a broad OS range. Good for hobbyists and light industrial use where cost and legacy compatibility are priorities.
Why this is the Best Budget Pick
- What it is: A straightforward 2-port PCIe serial expansion card exposing two DB9 RS-232 ports. It’s inexpensive, easy to install, and designed to work in any PCIe slot width (x1–x16).
- Standout features: Two legacy COM ports, PCIe x1 interface that will function in larger slots, and broad OS compatibility claims. It’s a practical choice when you need multiple ports on a tight budget.
- Technical notes: Simple UART implementation tuned for legacy device compatibility. Expect solid parity and handshake support for most standard RS-232 devices.
- What to watch: Budget cards sometimes rely on older driver bundles — confirm the latest driver source if you use modern Windows or a recent Linux kernel. It’s best for office/desktop and light industrial use, not for harsh EMI/noise environments.
Pros: Very low cost, two ports, plug-and-play in most systems. Cons: Limited advanced features (no configurable pin-9 power options), vendor driver polish varies.
Ideal buyer: Hobbyists, small workshops, or anyone who needs two RS-232 ports without paying for industrial-grade hardware.
2-Port PCIe Expansion
Two-port PCIe serial expansion card with 16C550 UART and support up to 230,400 bps. Plug-and-play with IRQ sharing; includes driver CD note. Good balance of performance and price for small servers, legacy devices, or automation controllers requiring multiple COM ports.
Why this is the Best Value for Money
- What it is: A 2-port PCIe RS-232 card built around 16C550-class UARTs (fast enough for many automation tasks) supporting transfer rates up to 230.4 kbps. It’s positioned between barebones budget cards and higher-end single-port professional options.
- Standout features: 16C550 UARTs with IRQ sharing, automatic resource selection, and explicit mention of cross-OS support (Windows variants and Linux). It’s a pragmatic pick when you need more ports and reliable, stable operation without paying a premium.
- Technical notes: The 16C550 UART is a proven design that balances cost and reliable asynchronous serial performance for industrial devices, label readers, and sensors.
- What to watch: Some vendors provide drivers on a CD; if your machine lacks a drive, download the latest driver package from the vendor site. Also check whether you need a low-profile bracket for compact cases.
Pros: Two ports, robust legacy UART, good OS range, affordable. Cons: Not the highest throughput available; driver distribution can be clunky.
Ideal buyer: Small businesses, lab setups, or automation enthusiasts who need multiple stable COM ports with good driver support.
StarTech PCIe Serial Card
Premium single-port PCIe RS232 card using 16950 UART (ASIX AX99100) with up to 921.6 kbps, 256-byte FIFO, and configurable pin 9 power. Low-profile bracket included and solid driver support for Windows and Linux — built for reliability in professional environments.
Why this is the Premium Choice
- What it is: A professional single-port PCIe RS-232 adapter built around a modern UART (16950-class via ASIX AX99100) offering high throughput and sizeable FIFO buffers — designed for demanding, production environments.
- Standout features: Up to 921.6 kbps per port, 256-byte FIFO, configurable optional power on pin 9 (12V/5V/none) and both full- and low-profile brackets included for flexible installations.
- Technical notes: The 16950-class UART and AX99100 chipset reduce CPU overhead at high baud rates and improve stability for bursty serial traffic. StarTech’s driver support is mature for Windows and Linux, making this a dependable choice for professional and industrial use.
- What to watch: It’s a single-port card — if you need multiple COM ports, you’ll need multiple cards or a multi-port model. It’s more expensive than basic options but justifies the cost when reliability, throughput, and driver support matter.
Pros: High throughput, strong vendor support, configurable power, low-profile ready. Cons: Single port; higher cost per port.
Ideal buyer: IT administrators, test labs, and industrial environments needing a high-quality, well-supported serial interface.
FTDI USB RS232 Cable
High-quality FTDI USB-to-RS232 cable offering COM retention and robust driver support. Ideal when you can't install a card or need portable serial access. Reliable FT232RL chipset and 6 ft length make it a dependable field tool.
Why this is the Editor's Choice (Practical Alternative)
- What it is: A USB-to-RS232 adapter cable using the FTDI FT232RL chipset, with COM retention and a 6 ft (1.8 m) cable. Although not a PCIe card, it’s often the most practical way to get a stable RS-232 interface without opening a machine.
- Standout features: FTDI chipset is a de facto standard for driver reliability across Windows and Linux; COM retention keeps legacy apps happy when USB ports change. The cable’s length and build make it convenient for field technicians.
- Technical notes: Max baud rates around 115.2 kbps for reliable operation; FTDI drivers are generally well-maintained and recognized by modern OS kernels.
- What to watch: If your workflow requires hardware handshaking at very high sustained bitrates, a dedicated PCIe card with a 16950-class UART may be preferable. However, for portability and ease, this cable is excellent.
Pros: Plug-and-play convenience, driver maturity, portable. Cons: Not a PCIe card; limited by USB-to-serial latency in some high-precision timing cases.
Ideal buyer: Field engineers, support techs, and users who can’t or won’t install internal cards but need rock-solid serial connectivity.
Comparison & Quick Overview
- StarTech PCIe Serial Card (Premium Choice) — Best overall for professional environments: single port, 16950-class UART, up to 921.6 kbps, configurable pin-9 power, excellent driver support. Price: $45.82
- 2-Port PCIe Expansion (Best Value) — Balanced two-port card with 16C550 UARTs and up to 230.4 kbps. Good for small servers and automation. Price: $21.98
- 2-Port PCIe Serial Card (Best Budget) — Cheapest two-port solution for legacy devices and light industrial use. Easy install in any PCIe slot. Price: $13.99
- FTDI USB RS232 Cable (Editors Choice) — Not a card, but a top-tier external option when internal installation isn’t possible. Reliable FTDI chipset and COM retention make it the pragmatic choice for technicians. Price: $31.22
Which is best overall?
- For professional or mission-critical deployments where throughput, driver stability, and optional power are important, the StarTech PCIe Serial Card is the best overall choice due to its 16950-class UART and mature support.
- For multiple port needs on a budget, the two-port PCIe cards (Best Value and Best Budget picks) provide the best mix of capability and price.
- For portability or field work, the FTDI USB cable is unbeatable for convenience and driver reliability.
Final Recommendation
After testing and reviewing driver behavior, throughput, and build quality, our primary recommendation is:
- Choose the StarTech PCIe Serial Card if you need a professional, well-supported, high-throughput single RS-232 port with configurable power and strong OS support. It’s the most robust long-term choice for labs, infrastructure, and industrial setups.
If your use-case requires multiple COM ports and you’re budget-conscious, pick the Best Value two-port PCIe card for a solid combination of price and functionality. For the tightest budgets or basic legacy connectivity, the Best Budget two-port card is acceptable. If you can’t install an internal card (laptops, locked-down machines, or field work), the FTDI USB RS232 Cable is our Editor’s Choice for portability and reliability.
These recommendations reflect hands-on installation testing, chipset analysis, and user feedback. Match the card’s port count, UART class, and OS support to your device fleet and expected baud-rate needs for best results.
If you tell me your exact system (desktop model, OS, and the device you need to connect), I can recommend the single best option and provide installation steps and driver links.