Why weren't there more motherboard mods for II series?

[Keatah]

Why weren't there more motherboard modifications for the II series? I'm talking about things like the shift mod. Or the Videx switcher.

 

Was it because there were 8-slots and all chips socketed? Was it because the board was perfectly designed and didn't need mods? Did the industry at the time shy away from cutting and soldering things on the mainboard? Would there have been minimal gains from any potential mod? Or maybe there were indeed more mods, like SeniorProm or NSC, that existed and I just didn't know about them?

 

Same goes with the IBM-PC. Don't really recall anything being done to the motherboard. Everything was on add-in cards.

Edited February 16, 2021 by Keatah

[ChildOfCv]

Most likely it was because the architecture of each one and its expansions allowed almost any mod one could dream of without modifying the MB.  It's kind of a waste to cut and hack when you can already get everything you need.  There may have been a mod to put a faster CPU in the PC, but by then you could already just buy a faster PC that had more capability anyway.

 

But you could already get parallel cards, serial cards, video cards, disk cards, CP/M cards, etc. for Apple II.  With the latter especially, it's plain to see that pretty much anything could be done without mainboard mods.

[Baldrick]

There wasn't much that was modifiable on the II+.  Sure you could get lower case character generators, and alternate ROM configurations (the programmer's aid chip comes to mind for the earlier Apple II) but generally most of the functionality you'd want to add would be on slot cards.

I have a couple of Unitron clones that included two prototyping areas on the motherboard and one of them had a circuit soldered to it that could redirect the Reset key, and another that could turn on and off interrupts from slot cards (unsure as to why), but because of the layout of the motherboard and the fact that it was completely stuffed, there was not too much you could add, really.  The Rev 0 and some early revisions of the Apple II also had small prototyping areas.

You talked about the Videx switcher - presumably the "Soft Switch" add on to the Videx Videoterm, but that was actually an add-on itself.  Sort of a bodge, though so I don't know if that fits your definition.

There was also the Videx Enhancer which was an alternate keyboard encoder (which was a rudimentary 6502-based computer in itself with static RAM, ROM and a 6504 processor (which was a truncated version of the 6502)).  That was a pretty neat hack.

 

99% of all other add-on functionality would be done via the data bus anyway, so that meant slot cards.  I remember being able to buy prototyping cards that you could mount your own circuits to, and doing lots of that sort of experimentation.  

 

Maybe that's the answer to your question?

 

With regards to the IBM PC, it never really struck me as a hobbyist's computer.  Most were bundled with copies of Lotus 123 and Wordperfect so guess how they were going to be used...

 

[Krebizfan]

The prices of expansion cards for the Apple II were often low enough that anyone considering making a motherboard modification would need to spend more getting the components. The two socketed CPU replacements were about all I can think of for the motherboard without using expansion slots. Apple also made it very affordable to upgrade to a newer motherboard further reducing the need to modify the board. 

 

The IBM PC/XT had a range of tweaks to the motherboard. The XT could have the motherboard improved to support 640 k with the addition of 256 kbit memory chips, filling an unused socket with a decoder chip, and running a single wire. Changing the oscillator to get a higher clock speed or switching to a V20 was common. The PC Jr and Tandy 1000 got an option to fix their of their major flaws with a daughtercard that plugged into the 8088 socket and provided both an 8088 and 8087. All the IBM PC related systems went through a brief period where the idea of reducing the frequency of RAM refreshes was popular, gaining a modest speed increase at the risk of crashing.