When I was 13 in 1994, I spent $3200 I've earned to buy a Compaq Presario 486 dx100...it was great...but unfortunately as much as I upgraded the parts to it, I never upgraded the cpu. It wasn't until 1998 I could afford to purchase a Pentium II-450 with a sound blaster awe 32 and a Voodoo Banshee all together. That difference from the 486/100 to the pentium II has been what I consider the most MAJOR upgrade pc wise. While I'm not exactly old or young in the pc thing, I also was massively impressed with how solid state memory changed how things are, but in my case it wasn't an ssd, but actually a 8 gig ram disk I messed with when my old Core 2 Quad 9500 (or somehting like that) had 32 gigs of ram back before ssd's were a thing. That kinda made me realize how sucky spinning drives were. Now ALL my systems require a ssd or nvme drive.
My most insignificant upgrade? Probably getting a 5960x in my main machine over my 5930k. Both are wonderful, but I ate a lot of humble pie realizing that I really didn't do things that justified the difference between the two until this year. Despite owning the 5960x for over 3 years now.
Wait, what? How? How did you earn what was essentially a bazillion dollars for a 13-year old?
Its very difficult to pick the most significant. If I really had to pick the most significant, I think it would be moving from a green-and-black monochrome display to glorious 4-colour CGA back when I was a kid.
So basically, in a kinda-descending order:
1) Going from green-and-black monochrome display to 4-colour CGA,
?) Going from CGA to 256-colour VGA,
?) Getting my first CD-ROM drive,
?) Going from PC speaker to AdLib sound card,
?) Getting a 3.5" stiffy drive in addition to the 5.25" floppy drive,
?) Going from AdLib to my Pro Audio Spectrum, included in the said CD-ROM drive package above, and finally
?) Getting my first SSD.
Bunch of people going to Q6600s and SSDs
Exactly my story. I had ATI Rage LT Pro to an 8x AGP 9700 pro... I even had additional heat spreaders on the ram. Hooked on BattlefieldThe ATI Radeon 9700Pro was a game changer for me. Coupled with the release of BF2, gaming just had never been better, or arguably since. The pinnacle of PC multiplayer gaming and graphics progress right there.
My first PC was a 486 SX 33. And as noted by many above, there were numerous mile stones along the way. But honestly, not that I miss all of the tinkering and spending money, but back then you had to upgrade something at least every 6 months to keep up with the latest games. And when you did that upgrade, you could almost always see/feel the difference (even in day to day activities). Unlike the last several years where you can upgrade anything and tell no difference at all. At least back then, you felt like you were actually getting something for your money.