zmodem.gbbs

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 Zmodem comes to GBBS!
 --------------------

This past summer, between writing different versions of Shrinkit and GS-ShrinkIt, I wrote Zmodem drivers for several different bulletin board
systems.  If you are the sysop of a bulletin board which uses GBBS's ACOS
language you can take advantage of a very good deal.

For $21, I will send you a copy of the Zmodem drivers which work with GBBS.

But before I go into a little more detail about this, let me explain a little
more about the Zmodem drivers.


 Features:
 --------

o  Both RZ and SZ completely conform to the public domain Zmodem 2.0
   implementation by Chuck Forsberg using 16-bit CRCs.

   Both Zmodem Send (SZ) and Zmodem Receive (RZ) are completely and correctly
   implemented and take approximately 4k of space in the GBBS "use" buffer
   along with an extra 8k of buffer space in auxiliary memory.

o  There are special versions of RZ and SZ which use the Apple IIc's
   vertical-blanking interrupts for timing considerations.

o  Speed.  Zmodem is a streaming protocol.  This allows for faster transfers
   than Ymodem and helps 9600 baud transfers go close to their theoretical
   maximum. 

o  Better error recovery.  Zmodem can recover from errors better than Xmodem
   or Ymodem.  If you have a really noisy line, chances are that Zmodem will
   continue the transfer long after Xmodem and Ymodem have given up.

o  Network friendly. RZ and SZ will not "jam" a network by sending XOFF
   characters in its data stream.  Instead these characters are sent using
   Zmodem's escaping mechanism.  What this means is that you won't have to
   setup your local node of PcPursuit or other service when calling a BBS
   that uses RZ and SZ.  No special parameters for your node should be needed.
   Just call and transfer.

o  Zmodem is a "batch" protocol.  Both drivers support sending and receiving
   batches of files.

o  Auto-Download support. If your terminal program supports Auto-Download,
   then using RZ with your BBS will automatically tell your communications
   software to begin downloading without ever touching a key!  

o  Download resumption. If you have a communications program which supports
   resuming a download after you have been disconnected while downloading
   a huge file... no problem.  Just call back and begin the download at the
   point where you left off.  These Zmodem drivers properly support doing just
   that.

o  SZ (the BBS end receiving a file via Zmodem) supports both upload
   resumption (if you, as a sysop, like incomplete pieces of files laying
   around on your BBS), renaming an existing file, or just deleting a file
   on the BBS which the user is trying to upload.  So, in the case of a
   duplicate file, you have great flexibility in what to do.

o  Automatic block resizing!  Xmodem sends files with 128 byte blocks.  Ymodem
   sends files with both 128 byte and 1k blocks.  Zmodem can use any block
   size up to 1k.  When downloading, RZ will take note of how noisy the phone
   line is and if there are enough errors RZ will halve the block size until
   some data gets through.

   If you have clean phone lines then RZ will start increasing the block size
   until it is streaming 1k blocks.  So, the cleaner your phone lines are: the
   faster your transfers will be.

   If during the course of a download the phone lines become very noisy then
   RZ will make the blocks smaller -- and if the line becomes less noisy later
   during the download, RZ will start sending larger blocks.

* Just a note.  At this time, although plenty of Macintosh and IBM PC
  communications programs like ZTerm and ZComm support Auto-Download and
  file resumption, I do not know of any Apple II communications software which
  does.  ProTerm 2.2 and prior do not support Auto-Download or file
  resumption, although it is conceivable that ProTerm 3.0 will (we can hope).


 What you need to use RZ and SZ:   
 ------------------------------

      An enhanced (65c02) 128k Apple IIe, IIc, or Apple IIGS      
      GBBS "Pro" 1.3 or later (preferably later)
      A good working knowledge of GBBS's language, ACOS.

 What your $21 will get you:
 --------------------------

      SZ and SZC (Send Zmodem and Send Zmodem for the Apple IIc)
      RZ and RZC (Receive Zmodem and Receive Zmodem for the Apple IIc)
      Notes on how to write a simple module for your BBS to support Zmodem
       transfers.
      
      The latest versions of ShrinkIt, GS-ShrinkIt, II+ ShrinkIt, and
       AUTO-Unshrinkit will be included as a bonus (since they are, after all,
       freely available).


Because I am keenly aware of the amount of piracy that a product like this
will undergo, the following stipulations have to be attached:

o  Please pay by check.  Orders received in cash will be returned.

o  I will wait up to 3 months until I have received 40 orders before shipping
   anyone's order.  This means that the sooner I receive 40 orders, the sooner
   everyone will receive their copy of Zmodem for GBBS.  If you are not
   prepared to wait a while -- because I can't predict how long it will take
   to receive 40 orders -- then please do not order this.
   
o  If I do not receive 40 orders, I will return everyone's checks uncashed.

o  I am not going to attempt to hunt down those who choose to illegally
   distribute what I write -- I would only hope that some of them have the
   decency to pay for what they use.  There isn't any tomfoolery in the
   drivers either.  No secret codes or encryption or serial numbers.  If you
   buy a copy, I will send you a copy.  It's as simple as that.


If this sounds reasonable to you, then send a check for $21 to:

        Andy Nicholas
        1180 Reed Ave, Apt 12
        Sunnyvale, CA  94086

and make sure you specify what kind of disk (3.5" or 5.25") on which you need
the Zmodem drivers -and- where to send the Zmodem drivers.

 About the Author:
 ----------------

I've written the freeware programs ShrinkIt, GS-ShrinkIt, ShrinkIt for the
Apple II+, and AUTO-UnShrinkIt (shrinkit archive scavenger/extractor) and am
currently employed by Apple Computer to work on the Apple IIGS Finder.  This
is work that I did before coming to Apple and work that I'm doing in my spare
time.  I believe in low-cost, high-quality software.  I also believe in trying
to get that software to as many people as possible.

At this time (1/27/91), there are tentative plans for the distribution of
Zmodem drivers for both ProLine and the Prime BBS system.  These Zmodem
drivers have already been written and tested, although I will almost
certainly not handle their distribution.

If you have questions about the Zmodem drivers, suggestions for future
versions of ShrinkIt, or suggestions for the Apple IIGS Finder, I can be
contacted on America-Online, GEnie, CompuServe, and the internet at:

                            America-Online & Genie: shrinkit
                                        CompuServe: 70771,2615
                                          Internet: shrinkit@apple.com

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