I apologize for stepping on any toes, and at the same time take my hat off to the programmers of Kicad.
But as an old old programmer I feel I must say something about Kicad’s version “BACKWARD”
compatibility. Who would want to build a house, and then later have to disassemble it because the tools used to build it are no longer compatible with the new tools purchased. Before trying to upgrade from 4.0.7 to 7+, I had a notion there would be issues. I was right. There were serious ones too. Then I tried going to version 5, the same things. My humble advice to anyone wanting to use Kicad is start with the latest version, and only upgrade if you are starting with fresh files. I hope more progress will be made with footprints, symbols , and 3d models too. It is possible to build software that is 100 % backwards compatible. The end product will win awards for perfection. Again my apologies for any ill feelings caused.
Hello @wil001
A strange post.
You write about moving from 4.0.7 to 7.0.X, which is forward compatibility and then you write about backward compatiblity as if this was the problem.
If you are having problems upgrading, please ask questions on this forum. That is the forum’s purpose.
I had a notion there would be issues. I was right. There were serious ones too.
What exactly? Maybe you can be more specific so the problems could maybe be solved. Just saying that there are problems without saying what exactly they are doesn’t help.
You feel how you feel . . . no need to apologise, I’ve gone from V5 to V6 and now V7 without issue so I can’t help with V4, but there are people here that have experience with V4 → V5 etc. I’m sure they can help if you still need/want help.
That library update bit us all as far as i can tell.
Things move smoother in this area the last couple releases though.
I can’t say my experience with two transitions (from v4 to v5 and from v5/6 to v7) gave me the same feelings as the OP describes. v4 to v5 can be bothersome if you do not follow the recommended ways but v5/6 to v7 is as smooth as it can get.
The point on backwards compatibility is also a bit odd as v7 introduced full compatibility with v5/6 designs.
The discussion, why new versions change file formats, break compatibility etc. comes up quite regularly here and the arguments do not really change. progressing with a software means things need to change, sometime quite drastically as the old structure does not support certain things or would make them way more complicated to implement then they need to be. maintaining compatibility for these deprecated concepts could be done in theory but would need additional development time in each release. as long as there is a clear method to update the old files and as long as older Kicad versions are still available for install, I would always vote to spend the limited time the Kicad developer team has on fixing existing bugs and introducing new features instead of maintaining backwards compatibility over multiple iterations of file formats.
I have had some issues with old projects, but nothing I could not fix.
In KiCad V4 and earlier, the graphics from schematic symbols was not stored in the project at all (by default) and this lead to problems when the original libraries were not available. Back then there were scripts to make the project independent of the libraries.
In KiCad V5. the [project]-cache.lib and the [project]-rescue.lib system was created, and this was a bit of an abomination. A lot of people did not really understand what these files were for, and quite often they deleted the [project]-cache.lib or they did not archive it, and this damaged the project without them realizing this. It only became noticeable when both the cache file and the original libraries were missing.
From KiCad V6 onwards things like this will not happen anymore.
KiCad can read old projects. There is forward compatibility, and this will remain in KiCad (Wayne himself said so in one of his talks). Most (all?) problems with converting old projects to newer KiCad versions is because projects are incomplete or got damaged somehow. I do agree that it was (too) easy to damage a project in earlier KiCad versions. But as I wrote before, KiCad has improved tremendously over the last few versions and such things won’t happen anymore.
I think the opposite, upgrade before library rot sets in, especially pre V6. It’s best to wait until the new version reaches X.0.1 or 2 though, as upgrade bugs have happened.
The only pain I have had was with footprint pad spacings shrinking a few years ago. This made tracks using 0603 resistors and SOT-23 transistors as bridges clash.
4.0.7 had an convoluted file format and project structure among other issues. Much of it is redone by 6.0. Best effort was made to support reading those old files, but even now we do find occasional oversights. We aren’t commercial software, we don’t have manpower to cover everything nor keep people’s interest using their volunteer time nitpicking away at every corner case that may exist. The way the old code was written especially was difficult to unit test as well.
If you have a issue upgrading from 4.0.7 to 7.0 or newer, please report it, that’s a bug.
I don’t remember any serious issue upgrading V4->V5, and so on. My first work (with 4.0.6) was to define all symbols and footprints I will use. When, having my libraries ready, I came to drawing my first KiCad schematic it just updated 4.0.6 to 4.0.7.
With upgrading V6->V7 the only issue was that at first run of schematic or PCB KiCad asked me to select files containing lists of my libraries and opened for it a window that didn’t allowed to select Windows system/hidden files. So I had to copy it somewhere else using file browser.
I just threw away a bunch of old ISA? cards that no modern computer board supports. Damned, I don’t even know if I remember the names properly now. 
Progress happens. Sometimes old standards just get left in the dust.
Dear RaptorUK,
I had over 10 replies to my “Disappointed” post. I do appreciate the response. Nevertheless, I will only upgrade with new projects being built.
Further explanation of my 4.0.7 project: This project was built with Kicad 4.0.7. It was and is flawless and had “0” errors and warnings. I have the projects gerbers, in addition to archiving the project. I must say the project was large and had several projects nested within. All under one name with each having separate names as to the function of the overall circuits. It works perfectly. I just was going to take a chance and try upgrading leaving the project in place. When I was finished and Kicad 7 had been installed, I wanted to proof the new install by opening up one of the projects. It opened the schema’s with net issues and the pcb was filled with warnings and errors. I spent several hours fixing the tracks, footprint overlap, annotation problems, etc. still had over 200 left. I mean the main board size had changed just enough to screwup the whole board. I tried to make it work but was totally unable. The people who replied to my post apparently had small projects with lots of air on their boards, I did not. My project was very tight.
It does say one thing, make those backups and make them frequently.
I think some of the repliers misunderstood my “Backwards compatible” statement. When anyone goes to upgrade the program, lets say for better understanding, source code added to existing source code and then wants to use the new compiler only to find out that it results in all kinds of errors. If the new compiler had been backwards compatible it would have seen the old source code, replaced the needed lines or words and automatically made the adjustments for the end compilation.
It’s not a Biggy for me. I am sure that the programmers understand what I am saying. Going from Version 4 to Version 7 I just felt there should have been most if not all the hurtles overcome. Again sorry for ruffling feathers. My program is intact and still perfect. I still would advise anyone hard core designer to not do the so called upgrade, but instead start all new projects with the latest kicad. keep the older projects separate.
God Bless and good luck with your projects.
Will001
You know you can ignore the warnings and errors?
KiCad has now lot more (possible) rules that can help to make sure the schematic doesn’t have errors and the PCB is designed in a way that can be manufactured. But if you see a DRC violation and say: “No that is ok, it should work that way”, you don’t have to change it, just ignore the violation. There is even a button for it.
fortunately, no one tested the opening of version 4 in 7, this is true… we don’t know what problems it had… I had errors with the transition from 6 to 7… when saving version 7, it broke the board by turning over the tracks… I accidentally I noticed this because I know my project well… and yes, it was fixed in about 3 weeks… In general, the idea of changing the format every year is not very popular, but since there is no permanent API, apparently it is necessary
Some people might be interested in trying if someone would share a problematic v4 project to migrate.
Hi, Thanks for replying.
As a matter of fact when I ran DRC first time, I had I think 400 errors and footprint overlays. A lot of tracks were not ended right. Thus “No end error”. Then then leds I had in the circuits could not be found. There was a bunch to say the least. But my original gerbers are intact and good. That’s the main thing. Speaking for myself, I find continually having to tweak something gets old and boring. Personally, I don’t think that is necessary if the programmer does it right. I can only imagine how it would be to have many hands in the pot. WOW Opensource is a plus BUT!!!
Thanks again
Will001
Thanks eelik,
I would imagine there are some who would love to dive right in there and make it work. However, seeing that this will be my last 4.0.7 project, it really is mute. I know that If I would have started my project in 7 things would be just fine. Just so happens it was built in 4.0.7 . Like I said earlier my gerbers are good. I have checked them on the manufactures site to make sure. It’s a big project that has 17 boards. Each board has it’s own functions. There are a few boards that are very dense and have a lot on them. The boards alone will cost me some pesos that’s for sure. But it’s one of those things that does not grow old.
Thanks again.
It’s not just you getting a working project, but some of us like challenges and want to make KiCad better by finding roots of problems. Yor project sounds like a valuable asset for that kind of hobby.
Yeppers, I am not a supporter of changing thing over and over. I mean heck, it’s a good way of destroying a damn good program. I suggest NOT upgrading with your older files. It’s just asking for grief that is not needed. And, if the circuit is not overwhelming like mine is, simply redraw it with all the new stuff. If mine had been1/3 the size that it is I would have entertained the idea of building it anew with 7. Maybe those in power can slow those programmers down. lol
Thanks and Good luck
Will001
You keep suggesting not to migrate to v7 but you don’t give us a chance to try to show you may be wrong.