One thing that was largely missing from commodity desktop computers 25 years ago was a ZFS filesystem.
ZFS added some genuinely important functionality that we now take for granted: snapshots, easy cloning, data integrity and zfs send/zfs receive for efficient replication and backups.
RAID existed in rudimentary forms since the 70s and 80s. See VAXcluster, and Ken Oiuichi's parity-based RAID patent from the 80s. The term "RAID" was coined by Garth in 87 or 88. PC-based RAID cards were available in the 90s. But: few people used them for small and home systems.
File systems with snapshots existed in the 90s. The extreme example was Alistair Veitch's Elephant file system (which never forgets), which was in the mid or late 90s. Again, normal PC consumers were happy to have NTFS and ext2.
Another major addition is virtualization on commodity desktops.
That's another technology that took a slow start. Full-on virtualization is a product of the 60s, and IBM's VM operating system. Where every user gets their own operating system (called CP/CMS), and hundreds of users share one computer. Now in the 70s, that computer was physically huge, it took a mainframe to run VM. By the 90s, most of the big computer companies were selling some virtualization technology ... LPARs (IBM), Domains (Sun), and so on.
The real breakthrough here was Mandel Rosenblum's work: In the early 90s, Intel's x86 machines were taking over the world for personal and commodity computers. Everyone thought they could never be virtualized, because the instruction set was such a horrible mess. Rosenblum and his grad students proved "everyone" wrong, and turned that into a lot of money with VMware. Today Intel virtualization is everywhere.
Some of the most significant improvements are not only having more CPU, RAM and disk space, but about what the system can actually do with those resources.
At the systems layer (underneath applications, meaning operating system, networking, and storage), the story of the last 25 years has been "democratization", with technologies (such as described above, plus high-speed networking and TCP/IP) becoming available to both the masses of individuals end devices and small servers, and to farms of small servers forming what today we call "the cloud".