2.1. Original Server Architecture

The original PC system architecture started out with one bus with a single speed and the same bus width to all peripherals, as illustrated in Figure 2-1.

Figure 2-1. Original PC system architecture.

Two main performance bottlenecks resulted from this architecture. First, because only one system bus was available for all devices, only one device could use the system bus at a time. When one device was using the bus, all other devices had to wait their turn for attention. Second, all bus transfers, both system and I/O, were restricted to the same bus speed.

In this architecture, approximately 96% of all data transfers were between the processor and memory.