SNI 3270 SNA Emulator Terminal

[Alex S. Crain]

In article <4037 at ihlpf.ATT.COM> gmark at ihlpf.ATT.COM (Stewart) writes:
>
>Has anyone out there had any experience with the SSI 3270 SNA
>terminal emulator for the UNIX-PC?  I've only used this type of
>teminal at IBM where it was of course hooked up to a non-UNIX
>system (years ago).  The speed was phenomenal, but not liking the
>system a heck of a lot, I didn't pay too much attention to it otherwise.

If you had looked at the back of your IBM terminal, you would have seen that 
it is connected with coax cable and DNC connectors, not the telephone wire
that ascii terminals use. The way IBM terminals work is that the terminal knows
what the screen looks like, and when the screen is supposed to change, the
computer sends the changes to the terminal, the terminal decodes the changes,
and the terminal fixes the screen. This is extreamly fast, because the terminal
does most of the work. the terminal also buffers the input, sending input
a line at a time to the mainframe.

The advantages to SNA are:
	Its REAL fast, sort of like putting your vt100 on the ethernet.
	The terminal server can use a network protocol, allowing zillions
		of terminals on the same system.
	Since many I/O functions take place in the terminal, The I/O overhead
		of the processor is reduced.

The disadvantages are:
	No character at a time input. Because of the input buffering, all input
		is held until the ENTER key is pressed. Thats whe XEDIT (The
		stock IBM editor) is so weird. Also, No EMACS.
	It only works on an SNA network. And SNA networks are usually only
		IBM mainframes.
	Its expensive. Roughly equivelent to a slow ethernet card. Which is
		roughly what it is.

-- 
					:alex.

nerwin!alex at umbc3.umd.edu
alex at umbc3.umd.edu