The King of Plug-and-Play: How USB Took the World by Storm

February 22, 2022 by Biljana Ognenova

Does anyone remember the time before the plug-and-play (P-n-P) method of simply “hooking up” devices with universal serial bus (USB) cables came to exist? Here comes a peek at the history of USB connectors.

Everyone, at one point or another, has experienced the "phenomena" that happens when trying to connect certain USB cables or devices; usually, the third time you flip it over, it finally fits in the port.

Connectors may not be the most "attractive" technology; however, they play a critical role when it comes to electronics.

In the past, occasionally, computer tinkerers had to inspect device documentation to check compatibility and perform card installations to help otherwise incompatible devices speak each other's language and complete assigned tasks. 

As with many practical engineering solutions, the USB connector resulted from one man's effort to solve an everyday problem—connecting his wife's printer to a computer. 


A high-level timeline of USB technology advancements.

A high-level timeline of USB technology advancements. Image used courtesy of Kensington


The engineer in question was Ajay V. Bhatt, now working as Chief Client Platform Architect at Intel, who came to the idea of the USB plug system inspired by electrical wall sockets.


The Computer Architect Behind USB Ports

Working as a team lead alongside Bala Sudarshan Cadambi, Jeff Morriss, Shaun Knoll, and Shelagh Callahan at Intel, Bhatt thought of the USB connector as the universal language translator of the communication paths for all external devices connected to a computer. 

Before the USB protocol innovation, messy hardware architecture was only a part of the problem for end-users; as the computer received multiple requests from different devices, prioritizing task requests was a second one. 


Ajay V. Bhatt, the computer architect behind USB technology.

Ajay V. Bhatt, the computer architect behind USB technology. Image used courtesy of Intel Free Press on Flickr


Bhatt helped solve this by creating different classes of data transfer connections for various devices. For example, designers gave less demanding devices (keyboards and mouses) priority connections called 'interrupt transfers.' 

On the other hand, designers gave other devices a choice to either use the faster and more erroneous 'isochronous transfer' or the slower and less erroneous 'bulk transfer.'

Although Ajay Bhatt holds multiple patents for his computer architecture inventions, the USB is not among them. However, the curious engineer doesn't seem to mind taking a practical approach to Intel's decision to make such a convenient device that is open-source and widely applicable, and above all else, user-friendly.   


The Shift Towards USB Standardization

The plug protocol turned out to be so convenient that initially reluctant big tech companies like Apple and Microsoft followed suit and were quick to implement the architecture for USB-enabled electronic devices. 

USB became the standard for plugging keyboards, mouses, cameras, printers, external drives, memory devices, and the currently essential charging port technology. 

The body responsible for USB standardization is the USB Implementers Forum, a non-profit organization whose members work on compliance and support of the Universal Serial Bus technology. 

Creating a unique standard system is by no means an easy feat for cable and connector variety. But if we look back at how convoluted peripheral device connection was three decades ago, a true change has been set in place.  


The Evolution of USB 

Since Bhatt's original 1.0 version from 1996 that could transfer 1.56 Mbps at a power transfer rate of 100 mA, USB connectors have improved many times, with data transfer of up to 40 Gbps and a power transfer rate going up to 5 A for the USB version 4.0.

The 1996 USB version included the Type A and Type B plug and receptacle, designed to provide host-to-peripheral power direction. 


USB Mini

The next big change came in 2000 when high-speed (480 Mbps, 500 mA) USB 2.0 was introduced. The 2000 version included the Mini Type-A (host device) and Mini Type-B (peripheral device) plug and receptacle, primarily designed for older smartphone models and some digital cameras. 


USB Micro

As smartphones evolved, so did USB ports — from a Mini to a Micro version, which came about in 2007. 

In 2008, designers enhanced the USB Micro port with a 3.0 software version and data power transfer of 5 Gbps at a 900 mA power transfer rate.    

Overall, the Type-A USB is the most common physical design found on today's computers. Type-A host port corresponds to Type-B peripheral devices and is designed to provide a uni-directional downstream connection. 

Although Type-A to Type-B power direction and design has the benefit of preventing two host computers from being connected to each other, it has its downsides. 

A common one is damaging the host port by plugging a Type-A USB cable into the corresponding receptacle on the wrong side up. As mentioned, it happens to everyone, at the least, by making one failed attempt to plug it properly the first time.    


USB Type-C

Designers found the solution to this common "upside-down" user problem in the Type-C USB, first introduced in a Macbook model in 2014. 


An example USB Type-C receptacle pin diagram. Screenshot used courtesy of Microchip


The Type-C is a symmetrically shaped oval with reverse plug functionality (there is no right or wrong side up). 

Additionally, it is markedly smaller (8.4 mm by 2.6 mm), comes close to USB Mini and is bi-directional, which means users can use it to charge one phone from another.  

With this innovation comes a push for USB-C charger standardization by the European Commission; if the change gets accepted, it aims to reduce e-waste significantly and help frustrated users get rid of different cables.    


Competing Technologies

Despite the widespread use of USB technology, nothing is ever perfect, even when it is universal. 

Those that swear by the Ethernet find Wi-Fi insecure and slow. Similarly, USB is not quick to be abandoned in favor of NFC or Bluetooth's wireless technologies, which are convenient for smaller files. 

Speed is crucial, and USB is still considered to be much faster. 

Wireless power transfer faces multiple challenges, too, and despite its advances, it is still a far cry from becoming a standard. 

Although the latest versions of the Thunderbolt cable are compatible with USB Type-C, the Thunderbolt has the advantage of providing more port types to connect external devices. 

It seems that Intel with Thunderbolt is always one step ahead of USB standards, raising the stakes for everyone involved by being more competitive. 

We'll see if this new innovation will result in the next "best" connective technology for everyone.



Do you remember the days before USB standards took over? What were some of your memories? What pain points do you recall? Share your thoughts in the comments down below.

1 Comment
  • pleriche February 25, 2022

    I still have my trusty RS232 breakout box, and used to carry a bi-colour LED with me at all times. It was very useful for checking which of pins 2 and 3 on a 25 pin D connector was TxD and which was RxD. Then came the 25 or 9 pin D-type to RJ45 adapters which made it easy to patch a room-full of VDUs to server ports with an RJ45 patch panel, or to change a straight-through to a crossover cable just by changing the adapter at one end. Clearly, today is Nostalgia Day. Just this morning I passed a gentleman of my generation or just a fraction older in the supermarket with his shopping list written on the back of an 80 column punched card!

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