Universal Serial Bus

Universal Serial Bus, or USB, is a computer standard designed to eliminate the guesswork in connecting peripherals to your PC.

Universal Serial Bus

  USB PlugThe Universal Serial Bus (USB) standard was originally developed in 1995, to minimize the number of ports in the back of the PC.  The major goal of USB was to define an external expansion bus which makes adding peripherals to a PC low cost and as easy as hooking up a telephone to a wall-jack.  USB featured a maximum bandwidth of 1.5Mbit for low speed devices such as mice and keyboards, and a maximum bandwidth of 12Mbit for higher speed devices such as web cams, printers, scanners and external CD-RW drives. Frustrated by Apples royalty fees on firewire devices, in April 2000, seven industry-leading companies, consisting of Compaq, Hewlett Packard, Intel, Lucent, Microsoft, NEC, and Philips published the specifications for USB2.0. It has taken approximately 2 years for USB 2.0 to become adopted as a mainstream USB1.1 replacement.  In just a few short months USB 2.0 will be the high speed PC peripheral connectivity choice over IEEE-1394.

Introduction to USB 2.0

Hi-Speed USB 2.0 logoThe USB 2.0 specification extends the maximum speed of the connection from 12 Mbps on USB 1.1 up to 480 Mbps (60MBytes/sec).  This enables the transfer of 1920x1080 images at 24fps (frames per second) for high-definition video conferencing or 320x240 images at 500fps for high speed video motion analysis.  The transition to USB 2.0 will be seamless, since USB 2.0 is both forward and backward compatible with USB 1.1. Older peripherals will simply plug into new USB 2.0 capable PCs and Hubs.  The USB connectors and cables are even identical.   It is even possible for a high speed USB 2.0 device to plug into a legacy USB1.1 port and simply operate at reduced throughput.   Both Hi-Speed USB 2.0 and original USB 1.1 peripherals can operate on a computer at the same time. The new USB 2.0 expansion hub design manages the transition of the data rates between the high speed host and lower speed USB peripherals, while maintaining full bandwidth utilization.   Up to 127 USB peripherals with 5 levels of hubs can be connected to a single USB host controller.  With 5 Meters (16.4 feet) of cabling between devices, a network of cameras, sensors, data acquisition, and I/O devices can physically extend up to 30 Meters (98 feet) from the PC.  A peripheral can either be self-powered or bus-powered, with up to 500mA of consumption. To satisfy the needs of low-power embedded and portable computer applications, a power-management mechanism is also incorporated.


USB has benefits for everyone. It helps to reach the first time PC consumer by overcoming usability barriers through easy peripheral installation. The end user has a more rewarding and productive experience.

Below is a table of current capabilities that USB has to offer:



Easy to Use Simply plug it in - everything configures automatically. True Plug-and-Play! Connect and reconnect peripherals without rebooting your PC.

Expandable Plug as many as 127 peripherals into one computer using USB multi-port hubs.

Speedy 100 times faster than serial ports -- up to 12 Mbits/second. With new USB 2.0 standards coming, the new target speed is 480 Mbits/second.

Standardized plug and port!

USB makes adding peripheral devices so easy, anyone can do it.

First, USB replaces all the different kinds of serial and parallel port connectors with one standardized plug and port combination. It looks like this:

With USB-compliant PCs and peripherals, you just plug them in and turn them on! USB makes the whole process automatic. It's like adding instant new capabilities to your PC. You never need to open your PC, and you don't need to worry about add-in cards, DIP switch settings or IRQs.

The USB On-The-Go (OTG) specification has added Mini-A and Mini-B plugs and receptacles to the original USB A and B connectors, along with a "Mini-AB" receptacle, to support smaller portable devices such as cameras and PDA's. These plugs and receptacles are considerably smaller than their original full-size counterparts (Fig. 1).

Just plug it in and go!

Thanks to another USB feature known as "hot-swapping" you don't even need to shut down and restart your PC to attach or remove a peripheral. Just plug it in and go! The PC automatically detects the peripheral and configures the necessary software. This feature is especially useful for users of multi-player games, as well as business and notebook PC users who want to share peripherals.

USB also lets you connect many peripherals at one time. Many USB PCs come with two USB ports. And special USB peripherals -- called USB hubs -- have additional ports that let you "daisychain" multiple peripherals (devices) together.

Another cool USB feature is that it distributes electrical power to many peripherals. Again, USB lets the PC automatically sense the power that's required and deliver it to the device. This interesting USB feature eliminates those clunky power supply boxes.

Control peripherals...

USB connections allow data to flow both ways between the PC and peripheral. This means you can use your PC to control peripherals in new and creative ways.

For example, you can use your PC to automatically manage a telephone call center to maintain voice, fax and data mailboxes, screen and forward your calls, and even deliver a variety of selected outgoing messages.

Or you can use your PC to tune a set of USB-compliant stereo speakers to match the acoustics of your listening environment.


USB 2.0—KISS (Keep It a Simple System)


Allyn Pon, Cypress Director of Product Marketing, Interface Products Division
Cypress Semiconductor, San Diego, CA

Simplicity. That's what PC users want, and if the industry is to grow, PC, peripheral, and IC manufacturers will have to provide it. In response, the PC industry developed USB, an interconnect technology featuring smaller connectors, easier installation, port expandability, and faster performance than legacy ports. In other words, USB is simpler and better—the reason why it will ultimately prevail over other standards.

Experience dictates that transitions to new technology work best if they provide significant user benefits, standards compatibility, industry support, transparency, and cost effectiveness. Let's see how USB 2.0 stacks up in these areas.

Significant User Benefit. USB 2.0 is fast. Most PC peripherals need bandwidth somewhere between 6Mbit/sec. and 75Mbit/sec., so USB 2.0's 480Mbit/sec. provides full bandwidth for everyone. Even one of the most demanding applications, uncompressed video, only requires 125Mbit/sec.

Simplicity. Despite the 40-times increase in bandwidth, USB 2.0 is still a simple "user obvious" technology. Small connectors, easy installation via plug-and-play, and only one cable type all contribute to the new standard's simplicity and ease of use. Only one connector style is needed for the entire PC system, the simplest system of any of the competitors.

Compatibility. USB 2.0 is fully backward- and forward-compatible with USB 1.1. Existing USB 1.1 peripherals will continue to work for PCs equipped with USB 2.0. Looking at it the other way around, most, if not all, USB 2.0 peripherals plugged into a USB 1.1-based PC will operate under USB 1.1 operating conditions. In either case, the system continues working flawlessly, and runs at the fastest common speed.

Industry Support. Today, just one year after the formation of the USB 2.0 Promoters Group, there are 19 silicon suppliers (and more coming) who have pledged solutions for this standard, including Cypress Semiconductor. USB 2.0 was demonstrated at the Intel Developer Forum last February. The final specification was recently released, on schedule. This type of momentum is unprecedented in the PC industry. With the task of learning USB 1.1 behind it, Microsoft is moving quicker than ever to incorporate USB 2.0 into current and future operating systems.

Transparency. There will always be a class of novice users who will benefit from having new technology work without their needing to know that it even exists. USB 2.0 uses the same cables as USB 1.1. The connector shapes are the same. The topology is the same. So if the user doesn't know the difference between USB 1.1 and USB 2.0, the system will still work.

Cost effectiveness. Cost is very difficult to compare, because a number of variables can influence the final cost of the product. Another I/O standard, 1394 (FireWire), achieves similar speeds to USB 2.0 and thus is a good model for comparison. The most widely accepted comparison standard is the use of gate counts to provide an apples-to-apples comparison. Vendors who supply USB 2.0 and 1394 solutions estimate that 1394 host controllers have two to three times more gates than do USB 2.0 controllers. Vendors also estimate that 1394 peripheral controllers have four to five times more gates than comparable USB 2.0 peripheral silicon. With Intel planning to integrate USB 2.0 host controllers into future chipsets, the system costs of implementing USB 2.0 will be incremental vs. the cost of adding a discrete host controller for something like 1394.

No other technology meets all of these criteria, which is why the USB 2.0 train is moving so fast.