[Tfug] Blameless Parts Trafficking

[Bexley Hall]

WorldCare has several NCD Explora 401 X-terminals.
These are definitely "an adventure in computing"  ;-)
(I'm a strong advocate of diskless workstations even
though their advantages are most evident in large
organizations with dozens or hundreds of such
terminals!).

For more information, try:
http://www.ncd.com/support/explora/400/

Physically, these are about the size of a small,
hardback book -- about 6" x 10" x 2".  They are
usually shown in their funky stand -- which holds
them "standing on edge" (i.e., 6" *tall*, 2" wide,
10" deep) to minimize their footprint on the desktop.

Connections to the monitor, keyboard and mouse
resemble those of a (PS/2) PC.  A keyboard and 3
button mouse come with the unit -- you supply
the "VGA" monitor.

Any multisync "VGA" monitor should work.  The terminal
can be configured in a variety of display resolutions
up to 1152x900.

Power is from a wall wart.  Since the device only
consumes ~20W, there is no fan.  Since it is diskless,
there is no rotating media.  Together, this means
*silent* operation!  Attach an LCD monitor and you've
got a low power, small footprint "console" suitable
for use in a bedroom or quiet office -- away from all
the noisey servers!

"CD quality" stereo audio is available from a 1/8"
jack.  There is also a tiny speaker inside the
terminal for beeps and bops -- though it is also
accessible via nasd(1) (the folks at NCD developed 
the NAS protocol).

A single PCMCIA slot.

A serial port (DB9) and a parallel port (DB25).

Comes with 8MB of DRAM (?) though this can be
expanded to 64M (I've seen claims of 128M capacity
but have never actually *seen* a 64M 72 pin SIMM)
using 60ns FPM or EDO 72 pin SIMMs (QTY 2).

The drawbacks (some are inherent in diskless
workstations, some specific to X terminals and others
a consequence of this particular *design*) are
primarily:
- only an 8-bit deep display (i.e., only 256 colors
  in the colormap at any given time).  However, the
  color *palette* (CLUT) appears to be 24 bits deep.
  So, you won't notice any degradation on most
  photographs.  But, switching between clients (aka
  applications... "windows") can result in colormap
  "flashing" (the color map of the focused window
  gets loaded which means the "logical colors"
  currently in use in some *other* window may no
  longer be available -- so the contents of those
  windows appear with bizarre colors while they do
  not have the focus).
- "only" an 1152x900 display (a small step down
  from a 1280x1024 display)
- network interface is 10BaseT.  You'll need a
  dual-speed hub/switch if your other machines run
  100BaseTX (or gigabit).  A more significant
  consequence of this is the limitation it imposes
  on display bandwidth.  If you're looking to
  display full screen "movies" or *games*, you'll
  be disappointed!  You don't have that big fat 
  *pipe* (e.g., AGP video) from the application
  (i.e., CPU) to the display!  OTOH, if you are
  a "typical" computer user browsing web pages,
  text, etc. you shouldn't feel constrained -- even
  if you're an adherent of one of the "bloated
  desktops"!  :>
- there is no audio *input*.
- the PCMCIA slot is only (??) useful for a flash
  memory card to optionally store the bootstrap image
  (and fonts, etc.) on a "local filesystem".
- "security" can be an issue *whenever* you exploit
  the ability of running an X Windows display remotely
  (since lots of traffic appears "on the wire"
  unencrypted).

The most *practical* downside of X terminals is the
level of expertice required to get them running.  :<
But, I can offer some help, here.  (I've been using
X terminals for more than a decade)

NCD terminals (I've played with about 6 different
models and all seem to follow the same gameplan) have
a variety of configuration options (can you spell
"kitchen sink"?).  I've settled on the following
scenario:
- power up the X terminal (and monitor)
- the terminal broadcasts a BOOTPc request
- a BOOTPs reply tells the terminal its:
	. IP address
	. netmask
	. IP of DNS
	. name (and location) of boot file 
	. name (location) of configuration file
- X terminal downloads its boot file from TFTP server
- boot code in the X terminal mounts NFS partitions
  from a remote file server to access its:
	. configuration file
	. font files
- X terminal downloads configuration files and fonts,
  as needed and *when* needed (i.e., if you invoke the
  "setup" menus on the X terminal and alter its
  configuration, the changes are *written* back to
  that configuration file)
- X terminal broadcasts an XDMCP request to identify
  hosts to which it can connect (actually, hosts that
  can connect to *it*!  :> )
- X terminal presents a list of hosts that
acknowledged
  its XDMCP request (i.e., hosts into which you can
  login)
- user picks a host from this list
- that *host* (running xdm, or some bastardization
  thereof) presents a login dialog to the user
- user specifies login name and password
- once logged in, xsm(1) presents a lost of "saved
  sessions" for the user to chose among (yuck! crappy
  grammar there  :< )
- user picks a session from this list -- or, a "fail
  safe" session (typically just an xterm and window
  manager)
- xsm(1) restarts registered applications for that
  session
- user runs any other clients (applications) as
  desired
- when done, user logs out
- the process then repeats with the issuance of
  another XDMCP broadcast

As you can see, the X terminal requires services of
external hosts to operate:
- BOOTP server for initial configuration
- DNS server to resolve names
- TFTP server for boot image
- NFS server for configuration files and fonts
- optional "font server" (i.e., xfs(1))
Plus, the host (or hosts!) to which the X terminal
will ultimately *connect* for clients/applications
(e.g., xdm(1)).

However, these services can all be provided on a
single host (e.g., I run them all on an old Sun SS5
tucked in a corner of my office -- as well as running
xdm(1) on that same SS5 so that *it* can act as a
"host"!).

Also, there are *so* many configuration options that
allow a variety of different environments to be
supported.  For example, the TFTP and NFS roles can
be reversed.  Or, lumped into a single service (i.e.,
entirely using TFTP or entirely using NFS).  Or, use
MOP for you DEC-heads.

rarpd(8) or dhcpd(8) can replace bootpd(8) for
terminal
identification.  xfs(1) is only required if you are a
fontaholic.  DNS can be replaced by a static list of
(name,IP) bindings (i.e., similar to hosts(5)).

Or, the process can be canned in NVRAM (i.e., "hard
code" the terminal's name, IP, etc.).  A flash card
can be used to store the boot image and fonts
"locally" thereby eliminating *all* of this overhead.

The terminal has other capabilities once booted (i.e.,
at the point where it is ready to broadcast its XDCMP
request).  You can, for instance, open a telnet
session
directly from the terminal to any other IP-accessible
host (*without* the intervention of any other hosts).
Or, connect directly to the serial port (i.e., you can
have a "window" that behaves as a conventional
"terminal"/"glass TTY").  I use this feature to give
me a free "serial console" for my Sun machines.

Aside from the centralized maintenance aspect (which
is what makes X terminals such a *win*, IMO, for a
business), they are ideal for use with headless
servers.  For example, I run all of my machines
headless (I don't want to waste space on monitors and
keyboards and mice for each of them).  I can then
sit someplace comfortable (and *quiet*) and access
any of the machines (even concurrently) without having
to be near the machine in question -- exploiting X
Windows to give me a sort of "networked KVM"...

There are a fair number of these units at WorldCare,
currently.  They are asking $10 for each kit (mouse,
terminal, keyboard and wall wart).  They are quite a
fun challenge to get running -- as well as *use*!

Hopefully I've covered all the *major* issues for
those folks who've never played with such beasts...
Sorry for the lengthy post!  Feel free to ask (here,
or off-list) if something isn't quite clear.  It 
would be a shame for these things to get scrapped :-(

We now return you to your regularly scheduled
broadcast...

--don


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