WHAT ALL THESE BUSES MEAN
BUSES IN GENERAL:
When you purchase your computer, you may have an option concerning what type of bus, or expansion slots, you would like in it. When you add a sound card, graphics card, or virtually anything to your computer, you will be using one of the expansion slots on the motherboard. The slots are all based on a type of bus, which is a set of standards that slots follow.
The type of bus is very important because it determines how fast what you are adding will communicate with the rest of your computer. For example, the same brand graphics cards are typically available for various buses. A graphics card on one bus will not perform as well as the same one designed for a faster bus.
DESCRIPTION OF BUS TYPES:
ISA (8 or 16-bit)
ISA is the first bus designed for the IBM compatible computer. It is theoretically capable of speeds up to 16 megabits per second. There are two types of ISA slots. 8-bit slots were first introduced with the IBM PC. 16-bit slots were introduced the 286 processor AT models. 16-bit slots are compatible with 8-bit cards; 16-bit slots are faster.
Microchannel (32-bit)
The Microchannel bus was designed by IBM to replace the ISA bus. It is much faster, and is capable of what is called Plug & Play. What this means is that when you add a card to a Microchannel computer, you typically don not have to change the interrupt and DMA settings on the card, as you would with most other buses. These functions are done via software. Users are able to take advantage of Plug'nPlay now on other buses with Windows 95 and PnP compatible cards. On an IBM PS/2, you need to use a setup disk every time you change something in your computer, even a video card. Microchannel slots are available almost exclusively in their PS/2 line. Microchannel slots are much faster that ISA, but never became popular because they are not backward compatible with ISA expansion slots.
EISA (32-bit)
EISA is the bus designed by other major companies to compete with IBM’s Microchannel. It is capable of many of Microchannel features, including Plug & Play. The major difference is that EISA is backward compatible with ISA. EISA did not become very popular because the performance difference usually did not justify the added cost. EISA is available from many different manufacturers, and is popular in network servers, where hard disk access is very important.
VESA (32-bit)
The VESA local bus slot was designed to speed up graphics in Windows. A lot of high end graphics programs ran very slowly in Windows because the ISA bus was just not capable of displaying today’s colorful graphics as fast as the computer could throw them at it. VESA is an inexpensive, effective solution to the problem. Although VESA was designed primarily for video graphics cards, other cards, such as disk controllers, have become available in VESA formats. A disadvantage of VESA is that you can only have up to three VESA cards installed at a time.
PCI (64-bit)
PCI was developed by Intel as the next generation bus. It supports the best features of previous buses, such as Plug&Play, backward compatibility with ISA, etc. It does not suffer many of VESA’s limitations; PCI can be 64-bit (taking advantage of the Pentium,) work with other CPUs such as the PowerPC, and can have more than three PCI bus cards installed simultaneously. PCI is capable of 132 megabits per second, but will easily outperform VESA on a Pentium, and will perform roughly the same on a 486. PCI was designed as a full fledged standard; it will work better with other type of peripherals, such network cards, hard disk controllers, etc., but it costs more than VESA.
PCMCIA (16 or 32-bit)
The PCMCIA standard was created as a standard way to add network cards, modems, etc. To notebooks. PCMCIA cards are usually about the size of credit card; about three times as thick, and plug into slots on the outside of the computer, saving users from opening their systems. PCMCIA supports Plug&Play, so very little configuring is required. Though they are very easy to install, PCMCIA cards are not as fast as other buses. The latest, 32-bit, PCMCIA, will be roughly half the speed of PCI or VESA. PCMCIA is becoming increasingly popular in desktop computers because of it’s ease of installation.
SUMMARY:
For most people purchasing 486 systems, VESA or PCI is what we recommend. For those investing in Pentiums, it’s usually worth it to use PCI. It also makes sense to invest in Pentiums now because of Windows 95. For 386 systems or below, ISA is dominant, with some VESA available. When buying a notebook, make sure it has at least two Type II PCMCIA slots. The others, EISA and MCA, are uncommon, and are being phased out by most companies. Be sure not to invest too much in either of these buses.