Intel i845 E and G - 1 architecture, 2 very good contenders
The Intel i845 chipset was Intel's first attempt to bring a cost effective solution to the Intel Pentium 4 processors. Before i845, i850 with the rather unpopular RDRAM memory was the only solution; this presented a sales nightmare. Intel originally released the i845 chipset to support PC133 SDRAM memory. While the chipset was rumored to have a DDR controller built in, no motherboard supported this feature. Due to licensing agreements with Intel and Rambus, Intel was not able to endorse DDR SDRAM on the i845 release.
When the licensing agreements expired, Intel immediately re-launched new B-Stepping classed i845 chipsets with DDR SDRAM support for up to 2GB PC2100 (DDR-266) memory support. This saw the Intel Pentium 4 become a semi-affordable solution. The release of the 533FSB CPU required Intel to have chipsets that supported this new speed (after all, we don't want another Coppermine incident on our hands), so Intel brought us two new chipsets for the Intel Pentium 4, i845E and i845G.
Intel i845E and i845G are almost identical in performance and pricing. The only major difference is the graphics system. The Intel i845G incorporates an onboard graphics engine into the Northbridge similar to how the graphics were integrated into the i815 chipset. The i845G supports AGP4x video cards as well so you don't lose external video options with an i845G motherboard. Intel i845E is simply the i845 B-Step with 533FSB, no changes in architecture.
For your reference, below are two images showing the architectural layouts of the i845E and i845G.