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ZMODEM

en.wikipedia.org

132 pointsturrini99 comments

> Introduced 1986; 30 years ago

Now I feel old. I remember when this was new and clever. Made downloading from BBS's much nicer over XModem. At 2400 baud or whatever was current then!

There were a bunch of different something-Modems around that time that fiddled around with window sizes, retransmission approaches, batch transmission, and so forth. In case anyone is wondering, there was a YModem (also developed by Forsberg) in addition to XModem and ZModem along with various variants.

I even interned for a small company one summer that implemented one of these for a timesharing service using Prime minis.

SModem was the best. You could chat with people while downloading files.

I really liked HSLink, since you could both upload and download at the same time.

https://en.wikipedia.org/wiki/HS/Link

YModem-ga FTW!

I was 12 years old. I had a 2400 baud and ZModem was the second greatest thing that year. Watching Haley's comet on my birthday would be #1.

Halley modems and Halley's comet!

Yup, the first problem with Xmodem was that it transferred sectors (as in CP/M) and thus file size was always padded with zeros to a multiple fof 128 bytes.

Then came Ymodem which fixed this, and then Zmodem which was considerably faster (windowing protocol) and allowed resuming interrupted transfers and handled CRC checksums.

The resume was the clincher. You'd spent over an hour getting 3/4 the way through downloading an enormous 1M file to drop to line noise. OK, start again...

Saving 400+ for a Courier HST to go an insanely fast 12k (very rarely). They beat everything else at holding a line though.

Saving for a Zyxel and get 16800 :) Lots of good memories for the Elite 2864ID (ISDN) and U-1496E.

I had a project ~15 years ago with several thousand FAX Clients, and interestingly we had problems with every hardware card or modem we used except the (even then quite old) U-1496E which worked without flaw, whatever customer send data.

As soon as you saved and bought, they announced 56k! Fun times. :p

Talking of modems, a place I worked around '90 had racks full of modems for customer dial-in. What never occurred to me until I saw it was each one needed a phone line - half the back wall was covered with phone points!

Some years later a project was trying to do caller ID to computer. Simple idea, ridiculous number of issues. We found one modem that actually talked UK CLI of the dozens that claimed to. UK Cable spoke US CLI.

I got my first modem in 1990 or thereabouts. For some reason there was still a lot of XModem use back then, but it was gradually replaced by ZModem.

Some years later, just before BBSes were obsoleted by the internet, several multiplexing protocols appeared which let you chat or play a MUD while downloading or even upload and download at the same time.

Can't remember any names, but these protocols were only popular for a very brief time before the internet took over.

I also recall some BBSes survived a while into the internet age by adding telnet ports. You ran your normal dialer software with a telnet driver that took the hostname as the phone number and then would end up running ZModem and the likes over telnet.

There are still BBSes surviving today accessible via telnet. You can still go play LORD, MajorMUD, TW2K...

I think autostart was huge for me, aside from faster transfers. It was ages ago, yet it was like yesterday.

I remember when we did our own zmodem implementation so we could bypass download limits. Large BBS' at the time had restrictions on how many KB you could download in a day, but they only counted completed file transfers. ZModem had a provision for restarting failed transfers, so it was normal for a transfer to fail before completion (call waiting!) and the user to come back later to finish it. Our implementation could receive the last packet successfully, then push the transfer back a few blocks (retries) and fail.

Shout out to the 519!

That's awesome :) I would have loved to get my hands on that version.

Leech zmodem, scourge of the 713.

It's still hard to match the convenience of moving files to and from a server with RZ/SZ.

If your terminal emulator supports it, it will see the trigger sequence emitted and start the modem protocol over your ssh connection and save the file.

Since it runs over your current ssh connection it's perfectly secure.

It's so much easier then switching to a local terminal to use scp to get or put a local file. Sure, I know it's not the most efficient protocol but with the speed of todays networks the kind of files you're dealing with when doing administration or development are more quickly transferred by not having to do the context switch.

If there's a mac terminal that will do scp that has shell integration on the host. I'd switch to that, but I haven't found one. Is there?

I agree ... I forget to do this these days but in relatively modern days I used to use sz/rz all the time ... circa 2000-2004 I guess ...

I still use sz/rz on an almost daily basis, for doing embedded system development. The system I work with is only accessible over UART, so rz/sz is the only way to transfer files to the host PC (well, the only convenient way; the other way is through JTAG, which is a PITA, and only useful for imaging, not just transferring some small data file from the running system).

Same here. UART isn't always the only option on my platforms, but if Ethernet, WiFi, or USB gadget is unavailable for whatever reason, sz/rz (from Linux) or loady (ymodem, from U-Boot) is usually the next best choice. Minicom makes using these fairly convenient.

Apparently iTerm2 can be used to setup lrzsz coupling [1]. I haven't tried it yet myself, but I'm going to! I really hope this works. It's such a pain to setup scp back to my workstation that if I need to do any real back and forth, I've been known to setup a reverse SSH tunnel just for getting scp to work. But even then, it's a pain. Zmodem would be so much easier (and make me a little nostalgic inside every time I used it).

[1] https://grack.com/blog/2011/10/26/automatic-file-transfer-in...

Looking b ack at stuff like Zmodem, it's instructive to compare the computing culture then and now. Back then, everything was so cryptic. Documentation was hard to find printed books, code and config was extremely abbreviated ( sometimes for legitimate technical reasons of storage capacity). It was all very off-putting unless you put w lot of effort into research, or ran in the social circles that already had data and knowledge.

Nowadays we have an embarassment of riches of information and community and expressiveness and usability (when the APIs aren't locked down by DRM and trade secrets)

The other thing about coding back in those days is, if you got stuck, there was no stack overflow. You had to figure it out yourself or maybe ask a small grpup of people on a BBS or at a user group. Also, there was hardly any open source so things that seem trivial now like persistance or fast data structures were considerable efforts.

The most striking thing to me was there was a huge amount of free-as-in-beer software powering the entire BBS "network" and lots of helpful communities but almost nothing was open source.

From what I could tell, it took a long time for the academic tradition of making the source available to work its way into the non-academic world. The academics were using UNIX and other mainframe/minicomputer systems, but non-academics at home didn't have much access to this stuff unless they got themselves an account somewhere they could access through modem. So everyone else was "raised" in the PC tradition, which came from MS-DOS and the 8-bit micros before it. There, there was a bunch of "shareware" and a bunch of freeware available on BBSes, but the whole idea of passing around source code so everyone could benefit or make modifications just hadn't even come up. I grew up on BBSes and the idea of having source code just never even occurred to me honestly, until I started hearing about it when Linux became popular in the early 90s. The first real open-source stuff (which was really Free software), which pushed it as a philosophy, had to be from RMS and his GNU project, but I never even heard of that until Linux came along, and I think it was mostly confined to the insular academic world before this. When Linux came along, the GNU project finally had a kernel and could be put together into an actual working OS, and at the very same time, the internet was really catching on outside the academic world (this is about 1992 remember), and the WWW was only a couple years away. I'd say it was the perfect trifecta: the already-existing GNU software and tools (glibc, gcc, etc. are really important for having a working OS and building stuff), the Linux kernel, and the new-found accessibility of the internet allowing global communication and collaboration.

It's kind of weird how certain computing platforms that died around this time period have frozen in time this aspect of the modern "sustainment" movements. For example, the Amiga scene these days is full of high-effort oddball software and hardware projects that are closed source and for sale (and likely to earn their creators literally dozens of sales).

You would have needed to get hold of a compiler then. Of the specific compiler that was used to compile that source, probably. A few hundred $ here and there, and hope it would compile on your machine.

RBBS-PC was a dominant server program (package? so weird) throughout the 80s that was open-source and written entirely in BASIC.

https://en.wikipedia.org/wiki/RBBS-PC

Another thing is that once you logged onto a bbs, that is what you would be doing until you logged off.

These days my computer is logged onto a number of computers via various protocols all at the same time (especially if you torture the idea a bit and consider each web site open an anonymous login).

Kermit was in the same space as Zmodem. I remember it fondly, as they were very progressive around "open source" way back in the early 90's, and probably earlier. They accepted what was essentially a "pull request" over USENET discussions forums from me to add a feature.

http://www.kermitproject.org/ckfaq.html

That's pretty cool, what feature did you add?

Basically a toggle to turn off character set translation for rlogin sessions, to get past an issue with network connected modems.

Except they were never open. You could download the code, but you were not allowed to distribute modifications to it.

The project was cancelled in 2011, and according to the web page it's open source now, and I think that the open sourcing didn't happen until then.

I did put "open source" in quotes for that reason. At the time, it what somewhat novel to be able to get the source code at all, and even more novel that the writers would accept code from end users to put back into the product.

>At the time, it what somewhat novel to be able to get the source code at all

Really? IIRC, in Jason Scott's excellent BBS documentary (you should go watch it. Like, right now. It's that good), Thom Henderson (from SEA. Remember them? I don't, because I wasn't alive. Which is why I have to rely on documentaries) said that it was expected in UNIX circles, which is where Kermit originated.

Or were you on PC? I don't know, I wasn't alive.

For commercial end users of SunOS, Ultrix, etc, most of what we used was closed source.

Kermit was not the only software you could get source code for. However, the entire ecosystem was much smaller than what exists today.

I'll concede it may have been different in more academic environments.

shrugs

Of course, in the early days of unix, you got the OS in source form, but those were long gone by then. AFAIK, a lot of independently developed utilities were distributed in source form, in part because it was common to have to edit the sources and compile yourself if you weren't on the exact same architecture as the author. But that's just what I've heard.

"... Jason Scott's excellent BBS documentary (you should go watch it. Like, right now. It's that good)"

Agreed. The BBS documentary is superb and really, really entertaining and engrossing. Especially the episode(s) on fidonet.

I honestly found the compression and artscene episodes more interesting than fidonet. Although fidonet was good too.

Link to BBS documentary :

https://archive.org/details/BBS.The.Documentary

Thanks. Many memories of acoustic-coupler time spent on Compuserve and local BBSes.

They were for the definition of "open" which was current then - ie that the source or specification was available.

This is open source but not free software. Open source is still better than closed.

I remember receiving a 2400' tape for our VAX 11/750 from Lancaster University (UK) containing a full dump of their Kermit repo. Having pulled off the relevant VAX/VMS, PC and various other program formats, we had a way to transfer files between a number in-house development systems. This would have been about 1983.

Who remembers IceZmodem? A backwards compatible protocol that allowed you to play Tetris or listen to .MOD files while downloading... and if you were downloading from an IceZmodem capable host, you'd even get increased download speeds!

http://textfiles.com/computers/DOCUMENTATION/izm-q&a.txt

> IceZmodem (IZM) v1.1 Protocol-Chat,DOS,Editor,MORE!

> IceSoft Software presents IceZmodem, an amazing

> new Zmodem file transfer protocol with 100%

> standard Zmodem compatibility and many enhancements.

> While transferring files you can chat with the

> remote user, shell to DOS, edit a text file,

> play Digital MOD file Music, or play games.

> You can even get 2 pages of system information about

> the remote computer. Sysops can view the dropfile

> to find out who is using the BBS. It has one of the

> best status displays ever and includes a Screen

> Saver. TurboTrans, a Zmodem speed booster, has

> helped to get 99% efficiency on some file

> transfers.

> This amazing protocol simply has to be seen to

> be believed! Supports Sound Blaster or DACs

> for music.

- http://archives.thebbs.org/ra90c.htm

I remember this - so awesome. I seem to remember the Sysop could break in and chat with you too.

Wasn't IceZModem fairly late to the game? I remember Texas ZModem was my primary ZModem software for a long time.

This submission is a ploy by the NSA and advertisers to further refine their demographic slot of "old hackers".

Kermit, zmodem, bbs, baud.

South Park's Member Berries are in full force here.

CoCo forever!

Hey, I recognized all of that software save ZMODEM, and I'm not out of highschool yet! Then again, I only know about it because I read The Cuckoo's Egg, and am totally obsessed with computer history.

But I think most of us would recognize baud, even if we've never worked with anything that you would measure in it.

Or recruiters are adding everyone who responds to their 'too old/overqualified' blacklists.

I miss the BBS days. Very few non-geeks around. The internet just isn't the same.

:-)

I think my mention of zmodem in the audio tcp/ip post the other day gave rise to this post.

Which means I'm double marked ;-(

Fun times. My first experience with modem file downloads was the ASCII Express protocol on my old Apple //. Cutting my teeth on modem init strings, and keeping current with file protocols helped me break into IT despite not having a degree in it.

For example: "What, your Xmodem transfer always fails on the same block... oh, you most have xon/xoff flow control turned on. Try swapping that &K4 with an &K3 instead."

At one wacky point in my career, I ended up supporting a program "SPC" (software protocol converter), that flipped zmodem over an X.25 network to SNA to a mainframe. It ran on an OS2/Warp box. I wish I was making that up. I really do.

This immediately reminded me of GIFLink.

It was a layer over protocols like zmodem that rendered images as they downloaded. Think of that for a second. Modems were so slow that you could watch the image line by line render to decide if you wanted to continue on with the download. Yes they were porn images.

I remember the "porn" images from the BBS days. They were pretty laughable really, usually just pictures of naked women, frequently showing only their bare breasts and obscuring the rest. I think they were frequently just scans from Playboy, which was rather tame.

Compare to these days, where there's all kinds of crazy hard-core stuff available for free with a quick Bing search, in both still-photo and video.

No disrespect but you weren't calling the right BBSs.

And if you were too overeager you'd be "finished" before the image got down to the first nipple...

Gif89 had interlacing, so people might not understand what GIFLink does.

Here's the spec for gif89: https://www.w3.org/Graphics/GIF/spec-gif89a.txt

Here's an example BBS file list (or CD Rom dump) with some utilities, including GIFLink (and others). http://www.terminate.com/download/factory.txt

GIFLK112.ZIP 198.803 19-10-93 GIFLink v1.12 - View transmitting GIF images while downloading

What people might not know is that GIFLink cost money. $30! But that would easily be saved if it reduced the amount of images being downloaded.

ftp://ftp.retronn.de/dos/dfue/TER500/DOCS/PROTOCOL.DOC

    GifLink                                   Filename: GIFLK112.ZIP  Price: $30

    A Zmodem that allows you to view GIF images while you download. Maybe a nice
    feature if you really spend hours and hours downloading GIFs.

I'm not sure when that price was active. (That text has a copyright of 1994 to 1997).

Maybe the file is available here? http://cd.textfiles.com/expandin/BBSUTIL1/

My impression of zmodem and kermit, from 13 years ago (remembering then from a decade prior's use):

http://dmd.3e.org/2003/12/zmodem-vs-kermit/

Kermit's design accommodated connections that zmodem couldn't (half-duplex, connections that don't let one send some control characters. seven bit connections, or connections between systems using ASCII and systems using EBCDIC), and the basic protocol was easy to write. You could use Kermit to send data between your C-64 and a Cray 1 or Burroughs Large system--and it was used to send data from the International Space Station to earth. Later versions supported sliding windows and large packets where possible and let one selectively quote characters, while still providing backwards compatibility with earlier versions.

Well, yeah, exactly. Kermit was slow and careful and pretty well guaranteed to get your data across correctly, eventually.

Zmodem was more of a fast motorcycle. Your data might not always make it there alive in a rainstorm, but it was quick and and had fun doing it.

My impression? Kermit worked (if slowly) when other protocols wouldn't. Back in college, when I dialed into the University and attempted to download files, Kermit was the only one that would work across the insane university network (you dialed into a DEC terminal server, then you would issue a connect command to the actual computer you wanted. You could attempt to get an 8-bit clean path by sending a break character to get back to the terminal server, issue another command, then resume the connection, but for some reason, that almost never worked in my case).

Surprised nobody mentioned BiModem in the comments (popular at least in Europe). Simultaneous up- and downloads, which was great to get keep those up/down ratios at their proper levels.

I remember it in the US, but I can't remember how widespread it was.

I loved BiModem. I used it to transfer files in both directions simultaneously while also chatting with the remote party. Very cool for the time.

BBSes: Yet another technology I missed, because I wasn't alive. Ah well.

Speaking of things that I wasn't there for, did you know TinyTIM's still up? Sketch (perhaps better known around here as Jason Scott) hasn't actually killed it because it's so cheap to run. Mind, nobody's actually around anymore, but you can explore the relics of a once-great civilization over at http://www.tim.org/.

I was a little kid connecting to the US gov list of 800 number BBSes and always had fun choosing Kermit as my protocol, but ZModem was much faster!

The trick was to split. ZMODEM down (or YMODEM before that) and Kermit up.

I remember trying out Zmodem early on, only to find that it obviously had some kind of bug in that it would reliably and consistently drop the line after a certain amount of data had been transferred.

Not so, of course - but unlike Xmodem and Ymodem which acknowledged every packet (and slowed things down), Zmodem would not constantly ack back to the host unless there was an error... So this triggered the modem's inactivity timeout, since despite the constant stream of data coming down from the remote system, there were no "keystrokes" or other packets travelling in the other direction. Hence, after X minutes... Line drop.

Easily sorted with a few AT commands, eventually. :)