Keyboards are essential peripherals in computing, serving as the primary input method for most users. Over the years, different types of connectors have been used to attach keyboards to computers, with USB (Universal Serial Bus) and PS/2 (Personal System/2) being the two most prominent interfaces.
Both USB and PS/2 keyboards have unique characteristics that make them suitable for different applications. While USB keyboards dominate the market today, PS/2 keyboards still have advantages in specific scenarios, particularly in professional and legacy computing environments. This blog post provides an in-depth comparison between USB and PS/2 keyboards, discussing their advantages, disadvantages, technical differences, and applications.
1. Understanding the Basics of USB and PS/2 Keyboards
1.1 What is a USB Keyboard?
USB keyboards use the Universal Serial Bus (USB) interface to connect to computers and other devices. USB technology, introduced in the late 1990s, has largely replaced older connection methods due to its plug-and-play capability, flexibility, and support for multiple devices.
Key Features of USB Keyboards:
- Hot-swappable – Can be connected or disconnected without restarting the computer.
- Widely compatible – Works with modern operating systems and devices.
- Supports multiple devices – Can connect via USB hubs and ports.
- Powered by the USB bus – No additional power source required.
1.2 What is a PS/2 Keyboard?
PS/2 keyboards use the 6-pin mini-DIN PS/2 port, introduced by IBM in the 1980s as part of the Personal System/2 (PS/2) series of computers. Although largely replaced by USB, PS/2 keyboards are still used in specific environments due to their low latency and direct hardware communication capabilities.
Key Features of PS/2 Keyboards:
- Direct connection to the motherboard – Ensures faster keystroke registration.
- Lower input lag – No polling, as keystrokes are instantly processed.
- No need for software drivers – Works at the hardware level without requiring additional software.
- Limited hot-swapping – Requires system reboot to be recognized.
2. Technical Differences Between USB and PS/2 Keyboards
2.1 Data Transmission and Processing
- USB keyboards operate using polling, where the operating system continuously checks for input signals at set intervals. The polling rate typically ranges from 125 Hz to 1000 Hz, meaning keystrokes are checked every 1-8 milliseconds.
- PS/2 keyboards function via an interrupt-driven system, meaning the CPU receives an immediate notification when a key is pressed, leading to zero lag and more efficient processing.
2.2 Plug-and-Play vs. Dedicated Port
- USB keyboards are hot-swappable, meaning they can be plugged in and removed without restarting the computer.
- PS/2 keyboards require a dedicated port on the motherboard and must be plugged in before system boot.
2.3 Compatibility and Driver Support
- USB keyboards work with almost all modern operating systems and devices, including desktops, laptops, tablets, and even gaming consoles.
- PS/2 keyboards are supported mostly on older motherboards and BIOS settings but may not be recognized on modern systems without adapters.
2.4 Key Rollover and Anti-Ghosting
- PS/2 keyboards support full N-Key rollover (NKRO), meaning multiple keys can be pressed simultaneously without any being ignored.
- USB keyboards are often limited to 6-key rollover (6KRO) unless using a high-end gaming model.
3. Advantages and Disadvantages
3.1 Advantages of USB Keyboards
✅ Plug-and-play functionality – No need to reboot the system when plugging in or unplugging the keyboard. ✅ Universally compatible – Works with all modern devices. ✅ Multiple connection options – Can connect via hubs, extenders, and wireless dongles. ✅ Supports additional features – Backlighting, programmable keys, and wireless connectivity. ✅ Easily replaceable – Widely available and convenient to purchase.
3.2 Disadvantages of USB Keyboards
❌ Higher input latency due to polling instead of hardware interrupts. ❌ Limited key rollover – Only high-end gaming keyboards support full NKRO. ❌ Dependent on USB ports – Can take up valuable USB slots.
3.3 Advantages of PS/2 Keyboards
✅ Lower latency – Interrupt-based data transmission ensures instant key registration. ✅ Full N-Key Rollover (NKRO) – No ghosting or input loss. ✅ Direct motherboard communication – Enhances security in certain enterprise environments. ✅ Ideal for legacy systems – Essential for BIOS access on older computers.
3.4 Disadvantages of PS/2 Keyboards
❌ Not hot-swappable – Requires system restart to recognize new connections. ❌ Limited availability – New computers often lack PS/2 ports. ❌ Requires dedicated port – Cannot be used interchangeably like USB.
4. When to Choose USB vs. PS/2
4.1 Best Use Cases for USB Keyboards
- Everyday computing – Ideal for general users, office work, and multimedia.
- Gaming – High-end USB keyboards with 1000 Hz polling can rival PS/2 performance.
- Laptop users – Wireless and compact options make USB keyboards the best choice.
- Multitasking environments – Supports multiple device connections.
4.2 Best Use Cases for PS/2 Keyboards
- Legacy systems – Required for older computers that lack USB boot support.
- Enterprise security – Used in environments where keyloggers on USB ports are a concern.
- Professional typists and programmers – Lower input latency and full NKRO.
- BIOS and hardware configuration – Ensures reliable keyboard function before the OS loads.
5. Future of Keyboard Connectivity
As USB technology continues to evolve, newer interfaces like USB-C and wireless connectivity (Bluetooth, RF, and 2.4GHz USB dongles) are replacing traditional wired keyboards. While PS/2 is becoming obsolete, some niche applications still require its advantages in latency and security.
Future advancements in AI-driven typing prediction, haptic feedback, and biometric authentication could further redefine how we interact with keyboards.
Conclusion
Choosing between a USB and PS/2 keyboard depends on the user’s specific needs. USB keyboards offer flexibility, ease of use, and modern compatibility, making them the best option for most users. However, PS/2 keyboards still hold relevance in specialized environments requiring low latency, direct motherboard communication, and full N-Key rollover.
Ultimately, as technology advances, USB keyboards will continue to dominate the market, but understanding the advantages of PS/2 keyboards can help users make informed decisions based on their computing requirements.