On most PCs, it is possible to add memory chips directly to the motherboard. You may also be able to upgrade to a faster PC by replacing the CPU chip. To add additional core features, you may need to replace the motherboard entirely.
Motherboard Integrated Components Describes several motherboard components, such as sockets, connectors, regulators, capacitors, chips, pins, battery, and jumpers. This page is from "The PC Guide".
Parts of the motherboard Describes some of the components on motherboards, such as I/O cables and connectors, floppy drive cables, and ATA/IDE cables. This page is from "The PC Guide".
PC motherboard and system device reference Comprehensive motherboard reference, covering all the major motherboard components. Looks at the physical motherboard, chipset, system buses, system cache, system resources, and the system BIOS.
Guide to choosing a motherboard This sites hosts an extensive collection of information on motherboards. Geared towards the motherboard purchaser, this site provides introductory information, as well as links to various motherboard product pages and manufacturer home pages.