Zero client is a marketing term rather than a feature description, so there is no single way to define a zero client. This isn't really an issue, however, as long as you understand the capabilities and limitations of zero clients.
A few tests will help show just how "zero" a client might be:
|Does it run Windows or Linux?||Definitely a thin client||Might be a zero client|
|Does it have wireless LAN?||Unlikely to be a zero client||Might be a zero client|
|Is there a configuration server?||Might be a zero client||Probably a zero client|
|Are there shared configuration files?||Probably a zero client||Unlikely to be a zero client|
|Does it have gigabytes of storage?||Definitely a thin client||Probably a zero client|
|Do you need to configure each device before use?||Probably a thin client||Probably a zero client|
An important thing to remember about zero clients is that they read their configuration from the network every time they are powered on. Some even load their firmware from the network with every boot. In contrast, thin clients must be triggered to rebuild their configuration from the network, normally running from a local copy of the operating system and configuration.
Some zero clients have a management tool that configures the client and delivers new firmware updates. The presence of a management console doesn't prevent the device from being a zero client, but if each client has thousands of settings, then it isn't very zero. A zero client should have a few dozen configuration settings, and the management console should make it easy to apply the same configuration to a large set of zero clients. In fact, it should be difficult to set a unique configuration on a zero client. Unique configurations defeat the purpose of zero clients.
If each client has thousands of settings, then it isn't very zero.
Zero client limitations
The key to the zero client's simplicity is also its most significant weakness. The zero client is simply an appliance to access a data center desktop; its capabilities cannot be extended. Remote display protocols have changed since the early days, and now there is often support for multimedia playback, multiple monitors and USB devices, but the demands we place on desktops have also developed.
Today, the major challenges for zero clients are wireless and unified communications. Because a zero client needs to learn its configuration from the network, it is hard to support wireless communications, which require configuration to access the network. Some vendors work around this by having the zero client cache the wireless configuration, then read the rest of the configuration from the network. This approach requires that the initial setup of the zero client be done on a wired network. Subsequent configuration can be done over the cached wireless setup.
You also have to be careful with reconfiguration because it is easy to get locked out of the client if the wireless configuration is broken. This necessitates returning the zero client to a wired network. Thin clients can more easily support wireless networks because they always work from configuration stored on the device.
Unified communication (UC) often involves a PC application using a headset and a Web camera to provide voice and video communications, such as Microsoft Lync. This class of application is difficult for a data center desktop to handle because it requires a lot of CPU and RAM as well as a fast network. UC inside a data center desktop accessed over a wide area network requires an expensive, high-performing WAN.
More on zero clients
The difference between thin and zero clients
Deciding on zero or thin clients for desktop virt
Why zero clients rule and thin clients drool
You can reduce these challenges by putting the UC application on the user's thin client. You must use a thin client for this because zero clients don't allow for additional applications. Plus, UC applications are typically written for Windows. Alternatively, you could put a physical device on the user's desk to provide the UC function. This is why Cisco built thin clients into some of its Voice over IP phones. You could also have the staff member use a smartphone as a UC client, possibly using the office wireless network for voice and video. UC is definitely an area of ongoing focus for data-center-based desktop products. We may yet see zero clients that support running a UC application over a WAN connection.
Which should you choose?
If you are delivering desktops from a data center, you will need to choose an access device. A good strategy is to start with a zero client and only move to a thin client if the zero client's limitations present substantial obstacles for doing business.
Zero clients come in a range of forms and cost. They are available to support all of the major data center desktop products. Zero clients can be used in LAN and WAN settings, and some can even be used in a work-from-home scenario. But just like everywhere else in IT, there isn't one tool or product that fits every requirement. It's essential to understand your requirements and the capabilities of different clients before making your choice. Don't get tangled in the definitions of zero clients and thin clients -- use the tool that meets your particular requirements.