A Mac Classic with 4mb of RAM without using the RAM expansion card

Make sure you document and publish this, I think people will find this useful. It would be awesome if this was the world's first 4MB hack of this machine! Did I mention you deserve much more views and subs?

What you didn't explain is that while adding one address line increases the amount of addressed memory by 2, dynamic rams use each address line TWICE, once during the RAS clock interval, and a second time during the CAS interval. Each DRAM ram address line is muxed between TWO CPU address lines, so the memory address is FOUR times as much when you add a single DRAM address line.

Adrian, you are such a nerd. I love it! Please do not loose it. Been watching your channel since the beginning and I love how much you have matured with your videos. Thank you do much!

Definitely the sort of nerd project that I absolutely love to watch!!

@6:55 nice voice change "motherboard" :P

The CAS pins are pin 17 on the chips if you don't skip the missing pins. Guessing whoever made those schematics never saw the datasheet of those memory chips, so they just didn't know to count the missing pins. Anyway, this is a super clever hack! It's possible someone could've worked out how to do this back in the day, but it would've required them to realise that the SE and the Classic use the same chip, despite the different part numbers, and have access to the schematics (or reverse engineer that part themselves), so it's pretty unlikely anyone would've figured this out. Also it still would've been cheaper to do the standard upgrade, since those higher density memory chips would have been much more expensive than the standard ones that the Classic used. But still, great job figuring this out! Hopefully it might help bring back a few machines that have a faulty PAL or LS174 chip.

Such an awesome mod for a Mac Classic, especially for those boards that may have been almost relegated to worthless because the PAL was broken. Whereas the LS logic chips are pretty easy to replace even today, those discreet logic chips aren't, because as you said the programmed logic isn't fully known for these custom ICs. Using this mod, none of that matters which is so cool!

What a pleasure to see you so happy when it freaking WORKS !

Even when you hit a setback, you're able to laugh and carry on. Very nice.

Okay just finished your video and I'm currently taking apart my Mac can't wait to see if I can get it to work. The main reason I want this is for the form factor. I have my Mac in a custom 3D printed case and need 4mb and couldn't work out how I was going to get it all to fit without making the enclosure much larger than where I want it to fit. Thank you so much for all your amazing videos.

I'm soo loving the devious ingenutiy, articulately explained in the intro. There's a nostalgic aspect too for this 60 year old, as in my 20's I did a similar mod to upgrade my 1MB ARM1 Acorn Archimedes to 4MB by piggy-backing DIL chips.

I love the “really small pizza box” idea you outlined at the end, the first time I saw these motherboards I was struck by how similar they are to say a ZX Spectrum. Tiny board, a CPU, a highly integrated I/O chip, sound, and memory.

f2 = Address error - f3 = Illegal Instruction - fA = Line 1111 and wow E isnt even on the list lol. This one was awesome Adrian. i was as excited as you to see the final result.

Congratulations! That's quite an accomplishment. Any RAM upgrade is good, but a default RAM upgrade like this is beyond great!

That was actually a very clean mod to run 4MB onboard. It's doubly nice that it's 100% reversible as well.

I am not a huge fan of Macintosh stuff, but this was an awesome mod! Very fun video.

I have watched a few of your videos and they helped me tackle some repairs. I was able to replace 2 failed ram chips on an apple 2e and it works great now even installed ic sockets. Then I was able to repair a multi meter that fell off a ladder and hasn’t worked since. Was a broken solder joint pad and trace on the surface mounted “clock crystal” I think. Now will be used for a bench meter since I don’t trust the repair for day to day work. Thanks for your thorough explanation of the repair processes. Much appreciated.

That is so cool mate! Mistakes in schematics are the worst (hello IBM 5150 reset line) but excellent work tracing and understanding the system rather than just blindly trusting and giving up. Excellent reverse engineering and hackery!

I don’t think I’ve seen anyone else attempt this! This is next level! Loved this mod. Awesome work Adrian! Superb video!

Highly unlikely that I would ever do this, having never owned anything Apple. The Apple, ][, Classic etc. where not that popular here in the UK. But this is so cool, and I just love the fact that you decided to give it a go!