It is known by anyone with a PC that a sound card is a must-have. There is hardly a PC without one anywhere. Today, with sound cards being so affordable, it is a piece of cake to turn your PC into a high-fidelity sound system. And, with even common business software using sound now, a sound card is a requirement for most software.

Like most everything in the PC industry, the choices are no longer cut and dry. We have different capabilities on each card, as well as interface differences. All of this will be discussed in this section.

From ISA to PCI

If you head on over to the computer store in your area to buy a sound card, you will find that there are now numerous PCI versions available. Why? Well, the ISA bus is old, and the bandwidth is rather limited. A stereo-CD data stream can be 1.4 Mbps, a large demand for the ISA bus. The PCI bus, on the other hand, offers a 100-MBps bandwidth or higher. Several simultaneous sound channels are no problem for the PCI bus.

There are other benefits to PCI. The PCI bus allows cooperative signal processing, which means that tasks can be shared between the main system processor and a separate audio processor on the sound card. This means that the audio signals are free of interference from other tasks.

One pitfall of the PCI bus arises out of older DOS applications. Legacy DOS applications are designed so that they require a DMA and IRQ to move audio data from the main system memory. This means they use Sound Blaster compatible protocols. These are only features of the ISA bus, not PCI. For this reason, there is a risk that older DOS games will not run with PCI sound cards.

There are workarounds for this ISA-PCI problem in DOS. Using special hardware, it is possible to redirect the PCI interrupts into the legacy space, in effect making them ISA IRQ’s. The DMA requirement for DOS is being handled by enhancements to the PCI bus protocol. The total effect is to provide DOS support for PCI sound cards.

So, lets sum up the pros and cons:

ISA




Pros
Low cost
Proven reliability
Sound Blaster compatible


Cons
Low bandwidth
Uses up IRQ’s and DMA’s.
Limited to 85-dB signal to noise ratio

PCI

Pros
Higher bandwidth allows better audio effects, i.e. positional audio
Requires less resources
Allows 90-dB of higher signal to noise ratio

Cons
Higher cost
Sound Blaster compatibility must be done via a workaround.