The entire ecosystem surrounding modern descendents of the IBM PC compatible.

Normally this would also imply an Intel isa, which dictated a multi-component chipset. (North bridge/South bridge) this in turn implies an multi-voltage power supply with a standard plug or plugs derived from the one in the PC AT.

The PC ecosystem also features a set of peripherals, such as floppy drives, hard drives, and CD-ROM drives. These peripherals have their own busses, starting with MFM, and now IDE and SATA. In some cases SCSI entered into the mix, but most consumer-oriented PCs did not use it.
These drives were also were powered by the same power supply as the rest of the PC, with an evolving set of connectors and electrical standards.

The Mac took a parallel course, but featured it's own set of proprietary connectors and buses, as well as SCSI, for years before converging with the PC ecosystem in part in later years.

Many of these de-facto and cloned standards were adopted by standards organizations, such as EIA/TIA and IEEE. They were joined by PCI buses, which were used in a diverse set of architectures, including Sun. Later serial variants were developed for the PC and Mac ecosystems, driven by demand for faster graphics accelerators, with a side jaunt to AGP.

At the same time, emdedded devices evolved around a simpler usually single-chip chipset, and often single voltage board designs, with the exception of the cpu core voltage in some cases. These largely used memory-mapped IO with periphrial chips coupled to the memory bus, as well as slower buses such as I2C and SPI. These devices were usually power constrained, having quickly moved into the mobile realm with early PDAs such as the Newton. They mostly developed around the ARM chip which so low power in the early versions that it could run without voltage on it's primary bus.

As the PC ecosystem has evolved, it is now largely built around the PCI bus. PCI is cpu agnostic, so the CPU can be replaced with a different isa while keeping the rest of the system intact.

The PC is also historically modular, so substitutions such as those you suggested can generally be made while keeung the PC nature of the system. M.2 is a modern bus that has veen adopted into the ecosystem primarily for laptops, though also featured in some desktops.

Modern emedded devices are begininning to feature PCI interfaces, though these are only recently appearing in consumer electronics. They have been used in storage-centric chipsets for much longer.

The PC also implies a modular memory bus, with chips or modules complying with a logical and electrical standard, and identifying chip that can be probed by the chipset. In some cases the modularity is reduced and the chips are soldered to the mainboard.

PCs have also begun to adopt single-chip chipsets and System-on-Chip designs, starting with some emdedded intel designs used in mobile tablets and the UMPC. These brought the classic north bridge and south bridge as well as graphics (in this case PowerVR coming from the emdedded world). AMD64 chips also began to include the memory controller on die, leading up to the mentioned APUs that can be powered with the help of a standard embedded power IC from a single low voltage source.