Several buses allow multiple devices to function at the same time, minimizing waiting time and increasing computer speed. The major rationale for having many buses in a computer design is to boost performance. Having more than one channel allows the processor to work on more than one task at a time, which is called multitasking. This section describes some common multiple-bus architectures. Single-Channel Architecture - Single bus structure with only one channel. This type of architecture is used by most 8-bit computers from the 1970s through the 1990s. The IBM PC/AT was an example of a single-channel architecture. It had a serial ATA disk drive interface (used with floppy disks) and a PS/2 keyboard and mouse interface (used with long cables). The CPU could communicate with the disk drive or keyboard/mouse using the appropriate port. There was no way for the CPU to communicate with both at the same time. If a second task needed the use of the keyboard and disk drive, the user had to shut down the first program to make room for the second one. Multi-Channel Architecture - Multiple independent buses with each able to communicate simultaneously with the processor. Each channel provides its own separate bandwidth so if one channel is not being used then other channels can still use the bandwidth.