In 1985, only a year after the first Macintosh came out, HFS (later referred to as "Mac OS Standard") was introduced and replaced MFS.  HFS required Macintosh System Software 2.1 and was welcome to support the HD20, Apple's first 20 megabytes hard drive that had just came out for the Mac 512K.  Can you imagine storing 50 floppy disks (400KB each back then) into a single device? Back in the day, this was huge!

Now, we could argue that HFS has "evolved" over the first decade of its existence, but this is not true.  It's just because the newer computers that were manufactured over the years evolved themselves and used more bits to address memory (both RAM and HDD).  Apple released multiple System Software revisions to take advantage of each new Mac that came out, which in turn increased max partition size a couple times throughout the first decade.  Unfortunately, they kind of forgot to also take advantage of higher bit count addressing to increase the number of blocks on HFS partitions (always capped to 65,535) resulting in a locked max hard drive files count of 54,536 (from which there is a cap of 32,767 in a single folder). This limit was never increased until eventually HFS+ came out to replace HFS and solved this problem.

But in a nutshell, the newer the OS, the larger partition it can address, because the system uses more bits in each request:

Important: The max partition size should not be confused with max BOOTABLE partition size.  On a PowerPC Mac (e.g. on a G3) a safe limit for a bootable partition is 120GB, however, late PowerPC models such as the G4 or G5 can boot partitions up to 200GB.  In any case, it is always better to just create a 120GB for your System Folder to boot and then it's safe to partition the rest of the drive however you want.

Pro Tip: Remember that even if you CAN format a 100GB HFS partition under System 7.5.2 to Mac OS 9.2.2, you probably would NOT WANT THAT.  The reason being 100GB divided by 65,535 blocks = 1.56MB, SO THE TINYEST TEXT DOCUMENT CONTAINING A SINGLE 1 BYTE CHARACTER WILL RESULT IN A WHOPPING 1.56MB FILE.

HFS+ (referred to as "Mac OS Extended") was introduced under Mac OS 8.1 in 1998 and it is still in use today (2021) but is slowly being replaced by APFS since 2017.

Note: Here is how to repartition any drive under Mac OS 9: https://web.archive.org/web/20080113201922/http://www.kenstone.net/fcp_homepage/partitioning_new.html