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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.


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

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

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
    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
/data/webs/external/dokuwiki/data/pages/archive/apple/zmodem.gbbs.txt · Last modified: 2019/05/17 09:32 by

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