Zero clients are similar to thin clients in their purpose -- accessing a desktop in a data center -- but zero clients require a lot less configuration.
Zero clients tend to be small and simple devices with a standard set of features that support most users. They also tend to be dedicated to one data center desktop product and remote display protocol. Typically, configuration is simple with a couple dozen settings at the most, compared to the thousands of settings in a desktop operating system. Zero clients load their simple configuration from the network every time they are powered on, which means the zero clients at a site will all be the same.
Zero clients support access to a variety of desktop types, terminal services, a virtual desktop infrastructure or dedicated rackmount or blade workstations.
Zero clients vs. thin clients
The basic premise of a zero client is that the device on the user's desk doesn't have any persistent configuration. Instead, it learns how to provide access to the desktop from the network every time it starts up. This gives a lot of operational benefits because the zero client devices are never unique. This contrasts with a thin client, which may have local applications installed and will hold its configuration on persistent storage in the device.
The original thin clients were much like what we now call zero clients. They were simple devices that gave access to a desktop in a data center. Two factors led to the evolution of thin clients into thicker devices. The first was PC makers' entry into the thin client market, and the second was a need to work around the limitations of remotely displaying a Windows desktop.
A brief history of thin clients
Thin clients became a mainstream product class shortly after Microsoft introduced Windows Terminal Server and Citrix launched MetaFrame, both in 1998. To enter this market, PC manufacturers cut down their desktop hardware platforms. They repurposed their PC management tools, reusing as much technology as possible from their existing PC businesses. This meant that a fairly customized Windows or Linux setup could become a thin client. But even a customized Linux build usually has local configuration and a fair bit of storage. As a result, these thin clients were not so thin, and their management tools could be relatively complex.
The other motivation to thicken clients was the need to handle rich media, such as video. Early remote display protocols didn't produce great results, so technologies for thin client video rendering appeared. These used media players on the thin client rather than in the desktop, transferring the compressed video stream over the network. Now the thin client needed video codecs as well as a local operating system.
Over time, optional features for USB redirection, a local Web browser, Voice over IP integration agents and multi-monitor display support were added. Each additional feature increased the configuration and complexity of the thin client. After a few years, thin clients turned into small PCs. Some even added PCI or PC Card slots.
These thicker thin clients get quite close to a full PC in terms of capabilities and complexity. Instead of simplifying management, the thin clients forced IT administrators to manage the device on the user's desk as well as in the data center. This is obviously not what we had in mind. Zero clients are a return to the simpler devices on user's desks with simpler management.
Operational and security benefits of zero clients vs. thin clients
Any worker can use any zero client because the zero client doesn't store anything unique. This gives workers the flexibility to access their desktops from any zero client anywhere in the organization, reducing the need for employees to carry laptops between branch offices or shared desks. An organization can simply provide desks with zero clients, with all uniqueness stored in the data center desktop.
Another benefit is that a new zero client can be shipped directly to the user. There's no need for desk-side support or preconfiguration. All the zero client needs is a network connection and a power source. For an organization with many branch offices, this simplicity saves time and makes it considerably easier to set up a new hire or support a worker whose device is failing. Companies can even keep a spare zero client at each branch, which eliminates shipping delays.
More on zero clients vs. thin clients
Hardware breakdown: Thin vs. thick vs. zero clients
Choosing and managing thin clients
Pros and cons of thin clients vs. thick clients for VDI
Zero clients usually load their configuration from the network, often from a few files and shared by every zero client at a site. Changing a configuration generally means changing these shared files and then rebooting the zero clients. Updating zero clients is generally the same process: Place a new firmware file alongside the configuration files and reboot the zero clients. The new firmware is automatically loaded when the zero client boots. This makes it fairly simple to keep zero client builds consistent, so long as users turn off their zero clients at the end of the day.
One common reason to deploy data-center-based desktops is to contain data so a company's intellectual property isn't distributed to every desk. Because zero clients usually have almost no persistent storage, there is far less chance of critical data remaining on the device. Also, the zero client doesn't run a general purpose operating system, so it's unlikely to be compromised by a virus or network intrusion. In fact, this lack of local storage is a deciding factor for deploying zero clients in some highly secured environments.
Zero clients provide these benefits without the intrusion of a local operating system. For example, users don't want to see how the client device handles the USB key they just plugged in -- only their desktop should care. With thin clients, however, a local operating system must identify and handle the USB device before handing it over to the remote display client and then the user's desktop. Besides this being a slow process, there's an increased chance that something along the way will fail. Zero clients simply hand the USB device directly to the desktop, resulting in a far more PC-like experience. Zero clients also tend to show a far leaner local interface, getting to the user's desktop with fewer dialogue boxes than thin clients.