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Is PS/2 Faster Than USB? Unpacking the Truth Behind Input Latency

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The short answer? It’s complicated. While the simple answer used to be a resounding “yes” for certain specific use cases, especially among hardcore gamers, the landscape has shifted significantly with advancements in USB technology. The perceived speed advantage of PS/2 (Personal System/2) comes down to a nuanced understanding of how each interface handles data transfer, specifically in the context of keyboard and mouse input. Let’s delve into the details.

Understanding the Core Differences: Polling vs. Interrupts

The key difference lies in how the devices communicate with the computer. PS/2 utilizes an interrupt-driven system. This means that when a key is pressed or the mouse is moved, the device interrupts the CPU, immediately notifying it of the event. This is often touted as leading to lower latency, because in theory, the CPU responds the moment the device sends data.

USB, on the other hand, generally operates on a polling-based system. The host controller periodically polls the connected devices to check for new data. The standard polling rate for USB devices has historically been 125Hz (meaning the computer checks the device 125 times per second). This polling introduces a potential delay, as the computer might not check for data the instant it’s sent. Thus, you will have perceived input lag.

The Rise of High-Polling USB Devices

The game-changer has been the development and widespread adoption of high-polling rate USB devices. These devices, commonly found in gaming keyboards and mice, boast polling rates of 500Hz or even 1000Hz. A 1000Hz polling rate means the computer checks the device 1000 times per second, reducing the potential delay to a mere 1 millisecond.

At this speed, the theoretical latency advantage of PS/2 becomes negligible, and in some cases, the advantages of USB can outweigh any potential downside. The most important of these advantages is flexibility. USB offers a far greater degree of flexibility in terms of device compatibility, customization, and functionality.

The Real-World Impact and Modern Considerations

While the theoretical differences are interesting, what matters most is the real-world impact. For the vast majority of users, the difference between PS/2 and a high-polling rate USB device will be imperceptible. Most people won’t notice the slight difference between the technologies in the grand scheme of things.

However, for highly competitive gamers, particularly those playing fast-paced games that demand split-second reflexes, the slightest edge can be crucial. Historically, this group strongly favored PS/2. Today though, it boils down to testing individual devices on the systems they intend to use.

Advantages of USB: Flexibility and Features

Beyond raw speed, USB offers several advantages over PS/2:

Plug and Play: USB devices can be connected and disconnected while the computer is running, without needing a restart. While the article suggests PS/2 works if you never unplug the keyboard, that argument is a workaround at best.
Wider Device Support: USB supports a vast range of devices beyond keyboards and mice, including external storage, audio interfaces, and more.
Hotkeys and Macros: Many USB gaming keyboards and mice offer advanced features like programmable hotkeys and macros, which are often not available on PS/2 devices.
Backward Compatibility: USB comes in a wide array of speeds. The speeds of USB are as follows: USB 2.0 offers transfer rates of 480 Mbps, USB 3.0 offers transfer rates of 4.8 Gbps, and USB 3.1 Type-C delivers a 10Gbps data transfer rate.

The Demise of PS/2 Ports

Perhaps the most telling sign of the times is the gradual disappearance of PS/2 ports from modern motherboards. As USB technology has improved, manufacturers have increasingly phased out PS/2 in favor of a fully USB-centric design. Today, you will rarely find a PS/2 on newer motherboards, laptops, and other modern devices.

Conclusion: USB’s Victory

In conclusion, while PS/2 may have once held a slight edge in terms of raw latency, the advent of high-polling rate USB devices, combined with the superior flexibility and features of USB, has largely rendered PS/2 obsolete. For most users, USB is the superior choice.

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Frequently Asked Questions (FAQs)

Here are some frequently asked questions regarding PS/2 and USB:

Is PS/2 still relevant in 2024?

For the vast majority of users, no. The advantages of USB outweigh any perceived latency benefit of PS/2. High-polling rate USB devices have largely closed the gap.
Can I use an adapter to connect a PS/2 keyboard to a USB port?

Yes, PS/2 to USB adapters are available. However, performance may vary, and it may not fully replicate the experience of a native PS/2 connection.
Do all USB keyboards have the same polling rate?

No. Standard USB keyboards often have a polling rate of 125Hz, while gaming keyboards may offer 500Hz or 1000Hz. Check the specifications of your keyboard.
Does USB 3.0 or USB-C offer any advantages for keyboard and mouse input?

While USB 3.0 and USB-C offer significantly higher data transfer rates, this doesn’t directly translate to lower latency for keyboard and mouse input. The polling rate of the device is the more critical factor.
Are there any security advantages to using PS/2?

Some argue that PS/2 offers a slight security advantage, as the port is dedicated to keyboard and mouse input and less susceptible to certain types of malware attacks that target USB devices. This is mostly theoretical.
Why do some gamers still prefer PS/2?

Some gamers who have been playing games for a long time still prefer PS/2 out of habit or a belief that it offers a marginally lower latency. Also, they may be using legacy systems that require PS/2. This has become far less common.
What is the maximum cable length for PS/2 devices?

The practical maximum cable length for PS/2 devices is around 10 feet (3 meters).
Does using a USB hub affect input latency?

Yes, using a USB hub can potentially increase input latency, especially if the hub is overloaded with multiple devices. Direct connections are generally preferred for gaming peripherals.
Is it possible to overclock a PS/2 port?

While there are some theoretical ways to try and overclock a PS/2 port, it is strongly not recommended. In most cases, this will not result in a noticeable improvement.
What should I look for in a gaming keyboard?

For the best gaming experience, look for a keyboard with a high polling rate (1000Hz), mechanical switches, anti-ghosting, and N-key rollover.
Is it possible for manufacturers to trick the system into thinking they have multiple HID’s (Human Interface Devices)?

Yes, some manufacturers use multiple HIDs to bypass key rollover limits. This is not always reliable and may cause driver issues.
Is it possible for PS/2 to be ‘hot plugged’ (plugged or unplugged while the computer is on)?

While technically possible in some systems, it is not recommended and can potentially damage the motherboard or the device.
With advancements to USB, why do some people still have PS/2 ports on their computers?

Older computers may still have PS/2, and are useful for legacy devices. Some KVM (Keyboard, Video, Mouse) switches also use PS/2 connections.
What transfer speed does PS/2 use?

PS/2 ports are low bandwidth, and it operates around 10 kbit/s.
Can I have PS/2 and USB peripherals plugged in at the same time?

Yes, in theory, computers can run both USB and PS/2 peripherals, but they may conflict. Having both peripherals plugged in may give unexpected results.