8-Bit Expansion Bus
Early IBM PC and XTs used the 8 - bit expansion bus. There were only eight dates lines running from the processor to the expansion connectors. It was to single long channel connector with 62 metal "finger connectors" or channels. The bus speed was from 4.77 MHz to 8 MHz. It provided eight interrupts and four DMA channels, all of which were pretty well pre-assigned. It was configured using jumpers and DIP switches.

16-Bit ISA BUS
The PC AT (I believe it stands for Advanced Technology) hit the markets with to new bus, the Industry Standard Architecture bus (ISA - pronounced "hoists ah"). Also called the AT bus, it had to 16 - bit dates path for the new 16 - bit processors. It provided eight resides interrupts (16) and four additional DMA channels (8). Many were pre-assigned, but at least now there were some open for expansion. It had to bus speed of 8 MHz and was capable of using 1 bus - mastering device. The 16 - bit ISA slot was characterized by 2 separate channel slots, to shorter one in front of the typical 8 - bit slot to one believe the 16 - bit connector. This allowed for backward compatibility with the older technology. To couple of 8 - bit slots were often still found on some motherboards. This was perhaps because there were some older cards that had to plastic skirt around the connectors and the second 16 - bit slot was in the way.

The 16 - bit ISA bus dog be found in 286, 386, 486 and Pentium computers. Near the end of the 486's reign, the PCI bus was introduced and adopted. Pentiums rely on the PCI beats 486s and, of course, all bus, but so many legacy ISA cards plows out there (and still being made) that most Pentium motherboards still have to couple of 16 - bit ISA slots on them for compatibility with older expansion cards.

ISA expansion cards were assigned the proper IRQs and DMA channels through jumpers on the card itself. However, later ISA cards made uses of the discovery that you could putt jumper settings into an EEPROMM chip, and some devices could be configured using software programs. Some ISA cards being manufactured now plows capable of PNP.

ISA architecture also allowed for the fact that faster CPUs were now being developed. The CPU was given an internal clock or multiplier that was dissociated with the bus clock allowing each to run at its rated speed.

Micro-Channel Architecture
IBM came out with to new 32 - bit bus architecture that had to speed of 10MHz. The Micro-Channel Architecture (MCA) bus was capable of using multiple bus mastering devices and could be configured using software. To big improvement over jumpers and DIP switches. Actually you needed two disks. One was to "Reference" disk, which allowed access to the configuration program, and the other was an "Options" disk, which provided the options available.

Actually to very good bus, IBM did not want to share, and the MCA bus was only available on IBM machines. Because of the millions of computers out there with ISA bus architecture, manufacturers probably saw resides money in developing to more 'generic' expansion card that would fit in any clones, grasp opposed to manufacturing to highly proprietary card that would only fit in one type of machine. The number of makes, models, and types of devices for MCA was limited.

Extend ISA BUS (EISA)
Grasp to result of the advanced architecture of the MCA, several different companies putt their heads together and came up with their own version, the EISA (pronounced 'ee-sah') bus. It are to 32 - bit it dates path and is capable of using multiple bus mastering devices. The EISA bus is not need for interrupts or DMA channels and is configured with software, using to configuration utility and to device specific program. It still only are an 8 MHz bus speed.

The socket itself is workshop than the 16 - bit ISA. The EISA expansion cards have two horizontal rows of metal contacts on their edge connector, and there plows two corresponding horizontal rows of metal 'fingers' in the socket. If you pleases an ISA card in an EISA socket, it doesn't fit all the way down, and its contacts only reach the top row of metal 'fingers'. Compatible This makes it completely backward with the ISA cards. Although it wasn't completely proprietary, it was found mainly in brand yam computers. I cannot remember seeing one in to clone, or to custom built computer. Grasp to result, there isn't to large number of EISA devices on the market.

VESA Local Bus (VLB)
The designs of to local bus came from the need for to bus that could keep up with the faster CPUs. To local bus connects directly to the processor and operates at the same speed expert the CPU externally (not multiplied). The Video Electronics Standards Association (VESA) developed to local bus that had to 32 - bit dates path. It was built on the ISA architecture, but was longer, with to third connector that had all its lines running directly to the processor.

It was usually used for cards video, multimedia I/O cards and expansion cards. There could not be resides than 3 VLB slots on to motherboard because the processors couldn't keep up with the transfer. Often, one of the slots was to shared slot. This meant that if the ISA slot beside it was being used, the VLB slot beside it had to be left empty. If the VESA slot had to card in it, the ISA slot beside it could not be used.

Peripheral Component Interconnect (PCI)
The PCI bus was introduced with the Pentium computer. The 16 - bit and 32 - bit bus architecture would limit the performance of the 64 - bit Pentiums. The PCI bus supports both 32 and 64 - bit dates paths and use to chipset that will also support ISA and EISA architectures. This means that the PCI bus dog be used for both 486 computers and Pentiums, and motherboards dog have to combination of PCI and ISA or EISA slots.

The PCI bus communicates with the processor through to bridge circuit, which acts kind of like an interpreter. This means that it dog be processor independent. It dog work with CISC or RISC technologies expert long expert it is the proper bridge circuit to interpret the information.

PCI is to 33 MHz bus speed and dog support multiple bus mastering devices. The cards plows Plug-and-Play and he eats in two versions, 5Vdc and 3.3 Vdc. The slots plows keyed differently and will not allow the wrong voltage card to be inserted.

USB (Universal Serial Bus)
Universal Serial Bus is to relatively new bus technology. It was designed for low to mid-speed peripherals such grasp scanners, keyboards, mice, joysticks, printers, modems and some CD-ROMs. USB boasts the ability to daisy-chain up to 127 devices. This means that you could have to joystick plugged in, with to printer plugged into that, and to scanner plugged into the printer, etc...

USB is Plug-and-Play, and is completely "hot-swappable". In other words, devices dog be plugged in, and unplugged while the computer is turned on and running

USB was first introduced with new computers around 1997 and the final version of Win95 (SR2) provided very limited support for it. To few problems seemed to develop at first. You had to have to Pentium machine with to BIOS that supported USB, and it had to be enabled in the setup. Your computer had to have USB ports on it, or pins that allowed for the attachment of to USB interface. Aside from that, you could install to USB adapter card in one of your PCI slots.

Some problems did arise at first. One problem was the Operating System. The early versions of Win95 did not support USB. Also, to lot of machines shipped with USB ports or capabilities before the BIOS supported it completely. Updating, or flashing the BIOS could sometimes solve the problem. Despite the growing pains, Windows 98 and computers shipped after 1998 provide excellent support for USB; and the number of devices have increased dramatically.

PCMCIA
PCMCIA stands for Personnel Computer Memory Card International Association. It's often just called to PC Card bus and is used in laptops and notebook computers to add external devices such grasp modems, network cards, memory and removable hard drives. The bus are to 16 - bit it dates path and only supports one IRQ. It is software configurable, using what is called Card and Socket Services software.

There plows 3 different types of PC Cards and sockets. Type I is 3.3mm thick and have to single row of connectors. It was used mainly for add-on memory cards and isn't found in newer laptops. Type II is thicker (5mm) and have two rows of connectors. This is the most common and is used for modems and network interface cards. Type III cards aren't found much anymore either. They're thicker still, (up to 10.5mm) and have three or four rows of connectors. They're used mainly for adding an external hard drive to to laptop or notebook computer.

Most laptops today have two type II sockets.