EISA - Extended Industry Standard Architecture

Extended Industry Standard Architecture (in practice almost always shortened to EISA and frequently pronounced "eee-suh") that extends the ISA standard to a 32-bit interface. It was developed in part as an open alternative to the proprietary "Micro Channel Architecture (MCA)" that IBM introduced in its PS/2 computers. It is a bus standard for IBM compatible computers. It was announced in late 1988 by PC clone vendors as a counter to IBM's use of its proprietary Micro channel Architecture (MCA) in its PS/2 series.

EISA extends the AT bus, which the PC clone Vendors retroactively renamed to the !SA bus to avoid infringing IBM's trademark on its PC/AT computer, to 32 bits and allows more than one CPU to share the bus. The bus mastering support is also enhanced to provide access to 4 GB of memory. Unlike MCA, EISA can accept older XT and ISA boards – the lines and slots for EISA are a superset of ISA.

 

EISA was much favored by manufacturers due to the proprietary nature of MCA, and even IBM produced some machines supporting it. It was somewhat expensive to implement, so it never became particularly popular in desktop PCs. However, it was reasonably successful in the server market, as it was better suited to bandwidth-intensive tasks. Most EISA cards produced were either SCSI or network cards. EISA was also available on some non-IBM compatible machines such as the AlphaServer, HP 9000-D, SGI Indigo2 and MIPS Magnum.

Micro Channel Architecture (MCA Bus)

Micro Channel Architecture is an interface between a computer and multiple computers and its expansion cards and their associated devices. MCA was a distinct break from previous bus architectures such as Industry Standard Architecture. The pin connections in MCA are smaller than other bus interfaces. For this and other reasons, MCA does not support other bus architectures. Although MCA offers a number of improvements over other bus architectures, its proprietary, nonstandard aspects did not encourage other manufacturers to adopt it. 

It has influenced other bus designs and it is still in use in PS/2s and in some minicomputer systems. The MCA bus was IBM's attempt to replace the ISA bus with something "bigger and better". When the 80386DX was introduced in the mid-80s with its 32-bit data bus, IBM decided to create a bus to match this width. MCA is 32 bits wide, and offers several significant improvements over ISA. The MCA bus has some pretty impressive features considering that it was introduced in 1987, a full seven years before the PCI bus made similar features common on the Pc. In some ways it was ahead of its time, because back then the ISA bus really wasn't a major performance limiting factor:

32 Bit Bus Width: The MCA bus features a full 32 bit bus width, the same width as the VESA and PCI local buses. It had far superior throughput to the ISA bus.

Bus Mastering: The MCA bus supported bus mastering adapters for greater efficiency, including proper bus arbitration.

 

Plug and Play: MCA automatically configured adapter cards, so there was no need to fiddle with jumpers. This was eight years before Windows 95 brought PnP into the mainstream!

MCA had a great deal of potential. Unfortunately, IBM made two decisions that would doom MCA to utter failure in the marketplace. First, they made MCA incompatible with ISA, this means ISA cards will not work at all in an MCA system, one of the few categories of PCs for which this is true. The PC market is very sensitive to backwards-compatibility issues, as evidenced by the number of older standards that persist to this day. Second, IBM decided to make the MCA bus proprietary. It in fact did this with ISA as well, however in 1981 IBM could afford to flex its muscles in this manner, while by this time the clone makers were starting to come into their own and weren't interested in bending to IBM's wishes.

These two factors, combined with the increased cost of MCA systems, led to the demise of the MCA bus. With the PS/2 now discontinued, MCA is dead on the PC platform, though it is still used by IBM on some of its RISC 6000 UNIX servers. It is one of the classical examples in the field of computing of how non-technical issues often dominate over technical ones. But one of MCA's disadvantages is that it has poor DMA controller circuitry.

 

Features of Micro Channel Architecture

I/O data transfers of 8-, 16-, 24-, or 32-bits within a 64KB address space (16-bit address width).

• Memory data transfers of 8-, 16-, 24-, or 32-bits within a 16MB (24-bit address width) or 4GB (32-bit address width) address space.

• An arbitration procedure that enables up to 15 devices and the system master to bid for control of the channel.

• A basic transfer procedure that allows data transfers between masters and slaves.

• A direct memory access (DMA) procedure that supports multiple DMA channels. Additionally, this procedure allows a device to transfer data in bursts.

• An optional streaming data procedure that provides a faster data-transfer rate than the basic transfer procedure and allows 64-bit data transfers.

• Address- and data-parity enable and detect procedures.

• Interrupt sharing on all levels.

• A flexible system-configuration procedure that uses programmable registers.

• An adapter interface to the channel using:

o A 16-bit connector with a 24-bit address bus and a 16-bit data bus

o A 32-bit connector with a 32-bit address bus and a 32-bit data bus

o An optional matched-memory extension

o An optional video extension.

• Support for audio signal transfer (audio voltage-sum node).

• Support for both synchronous and asynchronous data transfer.

• An exception condition reporting procedure.

• Improved electromagnetic characteristics.

SemiConductor - What is SemiConductor?

Semiconductors are widely used in electronics to make components such as diodes, transistors, thyristors, integrated circuits as well as semiconductor lasers.

A semiconductor is usually a solid chemical element or compound that can conduct electricity under some conditions, making it a good medium for the control of electrical current. Its conductance varies depending on the current or voltage applied to a control electrode. Semiconductor is use for manufacturing chips.

 

A semiconductor device can perform the function of a vacuum tube having hundreds of times its volume. A single integrated circuit (IC), such as a microprocessor chip, can do the work of a set of vacuum tubes that would fill a large building and require its own electric generating plant.

Direct memory access (DMA)

DMA stands for "Direct Memory Access" and is a method of transferring data from the computer's RAM to another part of the computer without processing it using the CPU. While most data that is input or output from your computer is processed by the CPU, some data does not require processing, or can be processed by another device.

In these situations, DMA can save processing time and is a more efficient way to move data from the computer's memory to other devices. In order for devices to use direct memory access, they must be assigned to a DMA channel. Each type of port on a computer has a set of DMA channels that can be assigned to each connected device. For example, a PCI controller and a hard drive controller each have their own set of DMA channels.

For example, a sound card may need to access data stored in the computer's RAM, but since it can process the data itself, it may use DMA to bypass the CPU. Video cards that support DMA can also access the system memory and process graphics without needing the CPU. Ultra DMA hard drives use DMA to transfer data faster than previous hard drives that required the data to first be run through the CPU.

An alternative to DMA is the Programmed Input/Output (PIO) interface in which all data transmitted between devices goes through the processor. A newer protocol for the ATAIIDE interface is Ultra DMA, which provides a burst data transfer rate up to 33 mbps. Hard drives that come with Ultra DMAl33 also support PIO modes 1, 3, and 4, and multiword DMA mode 2 at 16.6 mbps.

DMA TRANSFER TYPES

MEMORY TO MEMORY TRANSFER

 

In this mode block of data from one memory address is moved to another memory address. In this mode current address register of channel 0 is used to point the source address and the current address register of channel is used to point the destination address in the first transfer cycle, data byte from the source address is loaded in the temporary register of the DMA controller and in the next transfer cycle the data from the temporary register is stored in the memory pointed by destination address. After each data transfer current address registers are decremented or incremented according to current settings. The channel 1 current word count register is also decremented by 1 after each data transfer. When the word count of channel 1 goes to FFFFH, a TC is generated which activates EOP output terminating the DMA service.

 

AUTOINITIALIZE

 

In this mode, during the initialization the base address and word count registers are loaded simultaneously with the current address and word count registers by the microprocessor. The address and the count in the base registers remain unchanged throughout the DMA service.

After the first block transfer i.e. after the activation of the EOP signal, the original values of the current address and current word count registers are automatically restored from the base address and base word count register of that channel. After auto initialization the channel is ready to perform another DMA service, without CPU intervention.

 

DMA CONTROLLER

 

The controller is integrated into the processor board and manages all DMA data transfers. Transferring data between system memory and an 110 device requires two steps. Data goes from the sending device to the DMA controller and then to the receiving device. The microprocessor gives the DMA controller the location, destination, and amount of data that is to be transferred. Then the DMA controller transfers the data, allowing the microprocessor to continue with other processing tasks. When a device needs to use the Micro Channel bus to send or receive data, it competes with all the other devices that are trying to gain control of the bus. This process is known as arbitration. The DMA controller does not arbitrate for control of the BUS instead; the I/O device that is sending or receiving data (the DMA slave) participates in arbitration. It is the DMA controller, however, that takes control of the bus when the central arbitration control point grants the DMA slave's request.

What is ISA Bus?

The Industry Standard Architecture or ISA (Pronounced as separate letters or as eye-sa) bus began as part of IBM's revolutionary PC/XT and PC/AT released in 1981. However, it was officially recognized as "ISA" in 1987 when the IEEE (Institute of Electrical and Electronics Engineers) formally documented standards governing its 16-bit implementation. AT version of the bus is called the AT bus and became a de facto industry standard.

History

ISA stands for Industry standard architecture. It was the original IBM expansion bus and initially no standard was assigned to it. Its first version was the 8 bit bus and it ran at the speed of about 7 MHz.

In 1984, with the advent of PC AT (Intel 286), the bus width is increased to 16 bits and the frequency successively 6 to 8 MHz, 8.33 MHz and finally, providing a theoretical maximum of 16 MB / s (in practice only 8 MB / s as a cycle of two was used for addressing).

The second generation of PC's used 16 bit ISA expansion bus which also ran at the same speed i.e. 7 MHz initially. The later cards allow speed of 8.33 MHz for the 16 bit ISA bus. Nowadays the I/O devices are much faster than their speed but still the ISA connectors are usually included in PC's to make them is backward compatible with the slower ISA cards.

Current motherboards no longer include ISA bus, PCI bus replaced by the faster and Plug & Play.

ISA bus architecture

ISA bus architecture is the basis of personal computer. 8-bit ISA bus is used in single user systems with 80386 and 80486 processors. There are 24 address lines and '16 data lines in it. It operates at 8 MHz and 2 to 8 clock cycles are needed to transfer data. The data transfer rate of the system is less when 8-bit ISA bus is used with 32 bit processor having 32 bit address and data bus. So, 16 bit ISA bus is used to transfer data. Many peripherals such as disk controller, printer, and scanner can be connected to ISA bus.