Complex sentence: Many of the last 80486 motherboards featured PCI slots instead of VLB slots, but most still had either PCI or VLB slots alongside the still-ubiquitous ISA slots.
Split into simpler sentences: Many of the last 80486 motherboards made have PCI slots instead of (or sometimes in addition to) VLB slots. Most boards had either PCI or VLB slots alongside the still-ubiquitous ISA slots.