Virtual desktops: five popular flavours, explained

One of the big questions in technology for the last three years has been how end users will adopt desktop virtualisation. The answer, at least from some early adopters, seems to be "how won't we do it?"

A survey released by the Enterprise Management Associates in September found that companies with desktop virtualisation projects in place or underway were almost all using more than one method of delivery, ranging from traditional terminal services to server-based applications accessed through a web browser, according to Andi Mann, VP of research for the consultancy.

A typical Citrix XenDesktop virtual desktop connection takes up between 56Kbit/sec and 100Kbit/sec of network bandwidth, and can satisfy the needs of many users by running shared operating systems and applications on back-end servers, according to George Thornton, network operations manager for Texas; Montgomery Independent School District, which standardised two of the three schools it opened this fall on Citrix virtual desktops.

His users who need more power for graphics-intensive or number-crunching applications can use the same thin-client hardware, but connect to a virtual machine on the server that supports only that one user, along with the additional memory or processing power required. That requires more like two megabits of network bandwidth per second, so Thornton kept those connections to a minimum, he says.

With all of the market competition around desktop virtualisation, some users are confused about the pros and cons of the various options. Here's a snapshot of the major desktop virtualisation approaches and of the types of situations for which they might be appropriate.

1. Remote Hosted Desktops

What most people think of when they think "terminal services." A server runs one image of an operating system or application and many clients log in to it using connection broker software that is the only part of the software hosted on the client machine. Client machines operate only to show an image on the monitor of the application that user is sharing, and to transmit keyboard and mouse input back and forth.

Advantages: Low cost, high degree of control over data and applications.

Disadvantages: Performance depends on the quality of the network connection; display protocols often can't handle complex graphics; some applications designed for desktops can't run in shared mode on the server; inflexible for end users, who can't store data locally, use most peripherals, or move data back and forth using thumb drives. Does not work when disconnected.

Example vendor offerings: Software: Citrix XenDesktop; Wyse ThinOS; Microsoft Remote Desktop Services; Microsoft Enterprise Desktop Virtualization (MED-V); VMware View Manager. Hardware: Pano Logic Device, Remote; nComputing thin clients; Wyse thin clients; Sun Ray Ultra-Thin client; Symbiont Network Terminal; Rangee Thin Client

2. Remote Virtual Applications

What you get in every web application you've ever used. Differs from shared desktops in that the only thing required is a browser and standard web protocols (HTTP, HTTPS, SSL) to create secure connections and transmit graphics and data.

Depending on design of the applications (think Flash downloads) the end-user's machine may process some of the application's logic or graphics, or may only light up the monitor and send clicks to the server.

Advantages: Doesn't require that IT control the hardware or software environment of the end user.

Disadvantages: Doesn't allow IT to control the hardware or software environment of the end user, which could affect performance. Does not work when disconnected.

Example vendor offerings: Citrix XenApps; Microsoft Remote Desktop Services; VMware View; VMware ThinApps.