What Does “Personal Computer” Mean? Communicating a New Paradigm
By Matthias Müller-Prove in User Experience
Magazine: Volume 9, Issue 4, 2010
Abstract. This article is about desktop virtualization and the implications for the PC as we all have known it for the better part of 30 years. When we say “desktop,” we mean a category of graphical user interfaces which has its origin in Xerox PARC. Windows, icons, menus and a pointing device are essential to GUI-driven desktop systems like Mac OS, Windows, and Gnome. The desktop is a metaphor for providing a familiar environment to the user. To that extent, the desktop is virtual already, and we have to pay attention to the words we use to describe the shift toward cloud computing and to desktop virtualization, where the physical hardware on your desk or lap is less important. Early usability issues have been addressed to make the virtual desktop infrastructure (VDI) a reasonable alternative for enterprises with hundreds or even thousands of seats, or companies who want to provide “desktops” as a service.
What’s a PC anyway? It is easy to point at a computer box and assume that this is it. In fact, it’s not.
Things have changed significantly since the advent of the personal
computing paradigm. The idea of reserving an entire machine for just
one single user was absurd in the late 1960s. Then the future was
invented at Xerox PARC with the Xerox Alto computer (also known as the
Interims-Dynabook) and its graphical user interface with early
components of the desktop metaphor, Ethernet access, and laser printing.
Since the mid 1980s, PCs have become standard equipment for almost
every office and knowledge worker. Today, the family tree of PCs extends
from desktop PCs – placed on top of or underneath the desk – to
laptops, notebooks, sub-notebooks, net-books, and the like. However, all
these terms just refer to the form factor of the hardware case. They
miss the point of the personal relationship between users and their
The user is key in this equation; therefore it is the P in PC that
needs the care and attention of user experience experts. It’s the data,
the tools, and preferences that make up the user’s personal working
environment. Damage to or loss of any of these components can have a
severe impact on the usefulness and perceived robustness of the system.
This is most obvious for data loss, but tools that are not
backward-compatible have the same effect. Furthermore, an unexpected
change of user preferences, by updating the operating system, for
instance, causes a drop in efficiency because the user’s familiarity
with the system suffers when the system does not behave as expected any
The scope of the issue is even broader today than it was 15 years
ago, because network-based services and social software now draw the
user’s attention to the World Wide Web. Formerly local and private
documents are now transformed into social objects by uploading them to
photo, video, slide sharing, and collaboration and community sites.
What’s a PC anyway? It is the personal relationship between users
and their digital work environment with their documents, applications,
customized settings, and online data and connections that matter. The
hardware is only a means of lighting the pixels that make up a magical
window into the digital world. The PC continues to offer a familiar
local desktop environment, but regarding the online environment, it is a
mere access device that can be exchanged for any other computer with a
web browser and Internet access.
Things are changing once again and will make the computer box as
we know it obsolete – or rather, it will be replaced by a virtual box.
The requirements for PCs in large and medium-sized enterprises are
ease of administration, low energy costs, and, last but not least,
flexibility for employees to move to other work places, to work from
home, or to work mobile at any other location. Physical PCs do not
sufficiently address these requirements because the personal working
environment is confined to the hardware where it is installed and
running. An alternative is the virtualized PC, which runs the operating
system on emulated PC hardware. This is called desktop virtualization.
It is quite easy to confuse the “desktop,” as used in “desktop
computer,” with the one used in the “desktop metaphor.” The latter is,
in a sense, a virtual desktop already. Now, in addition, desktop
virtualization turns the computer into software by introducing a new
layer between hardware and the operating system. The virtualization
layer consists of a hypervisor that emulates PC hardware on top of a
host computer, to run standard operating systems, such as Windows or
Running thousands of desktop instances in data centers is quite
energy- and cost-efficient compared to the same amount of actual PCs.
And defining pool policies, for sizing, cloning and recycling of
desktops, as well as group assignments between user directories and
desktop pools, saves a lot of work for the administrator. He or she
decides if the assignment between employee and virtual machine should
either be personal, as it used to be with a PC under the desk in the office, or flexible to grant temporary access to PCs in call-centers, classrooms, or Internet cafes.
What’s left from the PC on the user’s end? There is still a mouse,
keyboard, and monitor. But, since all computation takes place in the
data center, neither a powerful CPU, nor memory, nor a hard drive is
required on the client side. The fan is obsolete as well, which leads to
an access device with no moving parts and no noise; thus, lower power
consumption, longevity of the client, and improved ergonomics at the
work place are advantages of the virtual desktop. Maintenance costs are
also low or non-existent, as, for instance, the Sun Ray thin clients
don’t even have a local operating system anymore. Mobile access to the
desktop session is possible with any RDP (remote desktop protocol)
client. And in another case, the Oracle Virtual Desktop Infrastructure
uses a Java-enabled web browser.
In order to deliver a competitive end-user experience to the
clients, certain areas need to be considered. CPU, memory, and storage
do not usually pose a problem on the virtualization side, because the
requirements for a specified number of machines can be estimated in
advance. The usage of other shared resources is more difficult to
predict, such as access to the network and the storage system by
hundreds of simultaneously running virtual machines. And when it comes
to motion graphics, the bandwidth between data center and thin-client,
as well as the client’s display performance, becomes an issue.
Response times are typically discussed in three orders of
magnitude from 0.1 to 10 seconds. A system response that takes longer
than 0.05-0.2 seconds is no longer perceived as co-instantaneous. For
example, a skilled typist produces 300 characters per minute. This
equates to pressing a key every 0.2 seconds on average. If the response
time is about the same, then the output is at least one letter late!
Between 0.2 and 2 seconds is the range where the user feels in control
of the system. The delay is recognized, but the loop of command and
result feels like a smooth dialog with the system. If an operation takes
longer than two seconds, a progress indicator should be displayed. But
even a progress bar cannot keep the attention of the user for longer
than 10 seconds. After that, the user has to recognize the system state
once again, and plan the next interaction steps to accomplish the task.
The measurements for the perceptual level, dialog level, and cognitive
level have been well known for decades. Thus, web developers should
remember that rich Internet applications should also respond in time, or
provide appropriate feedback to improve usability in cases when network
or computation latency is too high.
In order to perceive smooth animations, a fourth time range, that
is even an order below 0.1 seconds, should be considered. Movie cameras
use a standard exposure of 24 fps (frames per second). However, the
human eye is able to detect frequencies of 60 Hz, which is also the
typical frame rate for HD TV. And when it comes to games on large
screens with fast animations, rates up to 100 fps are necessary to
maintain the illusion of motion.
Today, games and other applications with high-frequency
full-screen updates, for instance, video editing or CAD, are out of
scope for desktop virtualization. But fast refresh rates are necessary
anyway for cursor movements and direct manipulation tasks such as window
dragging or scrolling through long documents. Otherwise, the user might
perceive hiccups in the flow, and may become confused or even irritated
by interacting with the system. Adobe Flash movies and other video
content should run smoothly as well. Here, it is better to sacrifice the
image quality a little bit instead of running out of sync between image
and sound. This is managed by the protocol between the thin client and
the virtualization server.
Desktop virtualization is ready for prime time because virtual
desktop infrastructure (VDI) systems provide a level of quality and
service for enterprise customers that is comparative to the classic gray
PC boxes. Flexibility, mobility, and total cost of ownership
considerations convince hospitals, universities, telcos, banks, and
other companies with hundreds or thousands of employees to deploy
virtualized desktops. For example, there was an installation for JavaOne
2009 at the Moscone Center in San Francisco. Throughout the week, every
conference attendee could access three personally assigned virtual
machines running Windows 7RC, Ubuntu 8.10, and OpenSolaris 2009.06. All
together, 12,000 desktops were created with four Sun VDI hosts, five
hypervisor hosts, and three storage servers.
The PC is no longer the center of the digital universe. On one end
of the spectrum, the user’s data and attention moves to social web
services; on the other end, the personal computer itself will move into
the data center and become part of the “cloud” service. New kinds of
business models are being developed right now. Sooner rather than later,
service providers will offer desktop as a service to companies of all