The Problem: Wrestling with Ports and IRQs
In the early 1990s, connecting peripherals to PCs was a mess. To use set up any PC, you had to utilize a handful of different types of incompatible ports and connectors. Most commonly, those included a keyboard port, a 9- or 25-pin RS-232 serial port, and a 25-pin parallel port. In addition, PC game controllers used their own 15-pin standard, and mice often plugged into serial ports or proprietary cards.
At the same time, peripheral manufacturers began bumping into data rate limits in existing ports used for peripherals on PCs. Demand for telephony, video, and audio applications was growing. Traditionally, vendors had sidestepped these limitations by introducing their own proprietary ports that could be installed as add-in cards, but that added cost and increased compatibility issues between machines.
And finally, adding a new peripheral on a PC was a headache. It often meant configuring technical details like IRQ settings, DMA channels, and I/O addresses so that they did not conflict with other devices installed on the system. (Average computer users don’t have to think about these anymore.) There had to be an easier way.
The Solution: USB
Relief would soon come in the form of a single port that could unify the industry: the Universal Serial Bus. USB originated as a 1994 joint project between eight high-profile firms: Intel, Microsoft, IBM, Compaq, Digital Equipment Corporation, NEC, and Northern Telecom. After development for the next year and a half, the group published the USB 1.0 specification on January 15, 1996.
What they came up with was a serial computer peripheral bus that used simple 4-pin connectors that were rugged and inexpensive. USB allowed up to 12 megabit-per-second connections (enough for network applications at the time) and could serve up to 127 devices on a single bus if chained together using hubs.
Best of all, USB was completely plug-and-play, which meant devices automatically configured themselves (or sought appropriate drivers) when you plugged them in. No more wrestling with IRQs. And unlike earlier standards, USB supported hot-swapping, which meant you could plug and unplug your peripherals while the computer was still running: no need for reboots when switching something as simple as your mouse.
At the time, the industry was also eyeing competing standards such as Firewire (IEEE 1394), Apple GeoPort, ACCESS.bus, and SCSI. But the simplicity and flexibility of USB won out—especially when vendors demonstrated they could create relatively low-cost USB chipsets for hubs and peripherals.
USB Appears in the Wild
The PC industry adopted USB slowly at first, with incremental improvements in the standard taking place over several years before widespread adoption took hold. Microsoft first supported USB in Windows 95 OSR 2.1 in August 1997 (and Win NT around that time as well).
According to ComputerWorld, the Unisys Aquanta DX desktop, announced in May 13, 1996, was the first PC announced with built-in USB ports, though other vendors like IBM may have beaten them to market. Reports in Byte Magazine say USB chipsets weren’t available at scale until mid-late 1996. Still, by the end of 1996, almost a dozen PC vendors had announced PCs that included USB ports—usually two ports per machine.
Even with some early support for USB from PC manufacturers, USB peripherals that could actually use the ports were few and far between until around 1998. Until that time, almost every PC still shipped with legacy ports, so manufacturers continued to develop and sell devices that used them.
One event changed the availability of USB peripherals dramatically. In August 1998, Apple released the iMac, a sleek all-in-one machine that ditched all of its legacy ports for USB. For the first time in over a decade, Apple had created a machine without SCSI, ADB, or serial ports, and Mac peripheral manufacturers were forced to jump into USB in a significant way.
While Apple can’t claim sole credit in popularizing USB (there’s a healthy debate about that on StackExchange), the heavy press focus on the iMac’s reliance on USB brought the port into the popular consciousness in a big way for the first time.
Soon, those Mac USB peripherals were also available for PCs with USB, and with healthy support for USB in Windows 98, lower-cost chipsets, and revisions to the USB standard, the PC market began to adopt USB with gusto around the turn of the 2000s. Eventually, cell phones began supporting USB connections as well, and the popularity of USB hasn’t slowed down since.
USB Through The Years
Since 1996, USB has expanded dramatically in capability, including support for newer, smaller connector types and much faster speeds. Throughout, the standard has been maintained by the USB Implementers Forum (USB-IF). Here are some highlights.
USB 1. 0 (1996): The formal introduction of the USB standard with Type A and Type B connectors. High-speed is 12 megabits/second, low-speed is 1. 5 megabits/second. USB 1. 1 (1998): This release fixed bugs in the 1. 0 standard, including issues with USB hubs, and became the first widely-adopted USB standard. It also introduced USB Mini Type A and B connectors. USB 2. 0 (2001): This introduced a new, higher-speed 480 megabit/second mode while retaining backward compatibility with USB 1. 1 devices. A 2007 revision introduced USB Micro connectors for the first time. USB 3. 0 (2011): The 3. 0 standard introduced a new 5 gigabit/second data rate called SuperSpeed. It also introduced new Type A, Type B, and Micro connectors with more pins to support the higher data rate. USB 3. 1 (2014): This increased the USB data rate to 10 gigabits/second. Around this time, the USB-IF also introduced the symmetrical USB-C connector, which can be plugged in either way and still work. (No more flipping your USB device around three times to find the correct alignment!) USB 3. 2 (2017): With this revision, USB climbed to 20 gigabits/second and deprecated the Type B and Micro connectors in favor of Type C. USB 4. 0 (2019): This standard is compatible with Thunderbolt 3 and supports up to 40 gigabit/second connections. All connectors other than USB-C have been deprecated.
The Future is USB
As of 2021, USB is still going strong, supported so widely that USB connectors have become de facto power sockets for charging smartphones, tablets, video game controllers, battery-powered children’s toys, and for novelty items such as coffee mug warmers and tiny desktop vacuum cleaners.
USB hasn’t stopped improving. USB4 shows the industry is serious about keeping the standard competitive as computers get faster and the data we shuffle between devices grows ever-larger.
It’s even making inroads—Apple’s iPad Pro tablets dumped their proprietary Lightning ports for USB-C, although Lightning still endures on the iPhone and many other Apple devices.
Happy Birthday, USB!
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