This was the "hot new thing" of 1997...
The general architecture is that instead of the common arrangement today where users have a general-purpose WinTel PC on their desk, storing some data on LAN servers in the back room as managed by users (that probably don't have a clue of how to manage the software and configuration on their computers), we have a smaller, diskless workstation on the user's desk which hosts some applications, and leaves others to actually run on the server in the back room. All data resides on the back-room servers.
It isn't as new as the publicity would suggest; the basic architecture was implemented and commonly used probably starting ten years ago using "X Terminals," where the "central server" was a network of fairly large Unix boxes, and the workstation was the "X-Term," a terminal primarily just smart enough to run an X server to display applications using the X11 Window System. The recent change is to add protocols specialized towards hosting the display of Microsoft Windows applications.
The first "Network Computer" implementors were HDS and NCD, companies that have been building and selling X terminals for a number of years.
The major difference between Network Computers and traditional X-Terminals is that NCs add a bit more software to the desktop box so that:
Java applications can run on the NC;
The NC hosts web browsing (e.g. the HTML protocol) onboard;
The window manager and perhaps other utilities run locally on the NC box.
These changes reduce the amount of data that needs to go through the network connection, the amount of computing power required on the server, and associated memory consumption on the server. The other significant change is that the overall system includes the capability to run MS-Windows applications on a central server and export the displays to the desktop NCs.
There are plans to provide some additional protocols for which servers would reside on the desktop box, such as a special protocol called "ICA" to allow display of typical Windoze apps that use Microsoft's "GDI" API. The application would, again, run on the central server, and be displayed on the desktop box. (Apparently Microsoft disapproves of the notion of doing this using the X protocols. Big surprise... I wonder if anyone will be able to write an "ICA" (Intelligent Console Architecture) client that can talk to X servers, thus circumventing this?) Recent work involves using Java-based applications to manage the export process.
This approach allows desktop machines to become much smaller and cheaper, as they will typically not need all of the wide array of peripherals that appear on the typical desktop PC. Typically, mechanical components including disk drives of the various types (CD, Floppy, Hard Drive) go away. With these items being removed, the desktop unit shrinks in size, price, and complexity of installation. For instance, IBM's early NCs were about the size of a paper notebook at 20x25x3cm, and weighed only 1Kg (about 2.2 pounds). And the insides of the unit were not tightly packed... It doesn't need to be even that large, although there is little value to making the unit much smaller than that.
American Airlines rolled out some of these Network Computers for airline maintenance centres.
The removal of mechanical components also improves reliability, and ventilation using convection may be quite sufficient, if one's desktop machine doesn't involve hardware that nearly requires water cooling.
A typical Network Computer doesn't need to be larger than a video game console; it would be a neat thought for Nintendo or Sony to turn one of their video game consoles into NCs. They ought to be able to sell reasonably powerful NCs for under $400.
Particularly valuable about the approach is the notion that you no longer need to configure PCs individually. Your configuration resides on the network, and can follow you around to whatever NC you use. If something breaks, it may be an entirely reasonable idea to "fix the PC" by throwing it away and replacing it with a new $400 box.
NCD config data:
As the NC desktop box omits various mechanical components such as disk drives, it is
(Pro)Cheaper than a PC
(Pro)More reliable than a PC (no mechanical parts)
(Pro)Consumes less electricity
(Pro)Produces less heat
Since the NC depends on running applications over the network, this:
(Con) Increases system dependency on network reliability
Windoze systems that connect to LANS are already "designed" to "lock up" if the network goes down; my PC "hangs up" a couple times a month due to this problem.
There is, mind you, some validity to this concern. If the LAN is down, there are likely still some standalone PC applications that will still be useful.
But network dependancy is steadily increasing in any case, reducing the importance of this. For instance, SAP's R/3 system requires that clients have a network connection to an application server in order to perform any work. If the network is down, no R/3-based work can proceed. And it is not uncommon for a LAN outage to cause peoples' Windows PC workstations to "lock up."
(Con) May consume more network bandwidth
This claim is highly arguable; at present, if I load the typical 5MB document off a LAN file server, change one page, and then save it, this means transferring that 5MB of data across the network twice. (With the pigginess of MS-Word, this doesn't represent a terribly large document...) The same sort of task on a NC needs the network bandwidth to handle just the pages that I view and modify. There are no large blocks of data that need to be moved around.
In any case, isn't it convenient that 10Base100 is now becoming cheap?
(Pro) Means that configuration information is backed up on the server, not on the PC.
If my NC breaks down, I don't lose one speck of work or configuration. Unlike the hefty reconfiguration requirements if my desktop PC were to need to be replaced.
(Pro) Configuration becomes independent of which desk I'm at.
If I go to someone else's office, I can just log in, and have my full environment there, just as I would at my own desk.
(Con)NC Applications won't be usable when people are on the road.
This presumes that the applications in question previously were usable when people were running remotely... For instance, running client/server applications like SAP R/3 already requires a network connection at all times.
And this criticism implies that:
Java applications can't be run on a laptop,
HTML-based apps can't be run on a laptop, and
Windoze apps can't be run on a laptop,
Salescritters obviously won't be carrying NCs out to visit clients. But they weren't running mainframe host-based or Client/Server applications on the road anyways...
(Con) More disk space will be used on the servers
Maybe... But there's all the desktop disk drives that just went away. There will be programs and files that used to be stored on every single PC, where now only one copy needs to be stored and maintained. Instead of 50 copies of Word consuming enormous amounts of disk space on 50 PCs, there only need be one copy.
(Con) Running all those piggy Windows apps on a central application server means having a rather hefty central server, in terms of disk space, memory space, and CPU power.
You saved (say) $1000 by buying a NC rather than a PC; some of that $1000 obviously needs to go into the server infrastructure.
Supposing you need 16MB of RAM and 1GB of disk on the app server per NC, which likely overstates things, that still only costs about $300 per NC, which doesn't eat too badly into the other cost savings. At the "extortive" rate of 32MB per NC, a server with 1GB of RAM could service approximately 32 NCs, and that probably also represents about all the CPU load that a 2- or 4-way SMP machine could handle. (I've seen reference to the claim that Citrix Winserver can scale to around 200 users on an 8-way SMP box with P166 processors, so that this may, if anything be a conservative estimate...)
(Keep in mind that since the app server doesn't have to display graphics, both RAM and CPU requirements are diminished from what would be required on a PC that has to do both...)
(Pro) Since all code and data resides on the server, it's feasible to have everything backed up.
Since more data resides on the server, there will presumably be more to back up than there would be on a LAN server, when users have portions of their data sit on their own PC's hard drive in a nearly unprotectable form, so bigger tape drives such as the 20GB DLTs (see Excite search for +DLT tape scsi for more details) may prove necessary. Or an automated DAT tape changer system.
(Con) If the server goes down, then the NCs can't do any work...
And if the LAN server goes down today, what happens? Exactly the same thing...
Obviously this is a situation where Microsoft operating systems run at a disadvantage, as they are not very robust. It is not unusual for a network outage to knock out Windows-based clients; NC merely makes this a little more explicit.
LTSP is an open source project to create the administration tools that will make setting up a diskless workstation easier. Hardware can be found from Diskless Workstations.com.