Extended Industry Standard Architecture (EISA) Explained

What is Extended Industry Standard Architecture (EISA)?

EISA or Extended Industry Standard Architecture refers to the specific standard for IBM compatible computers which is an upgraded version of ISA and is fit to be used in high-end processors and computers.

Technically, the Extended ISA is designed to perform better than ISA with its 32-bit slots that allows a higher data cycle rate of up to 8.33 MHz using a wider data path but can also accept a 16 bit ISA card in the foremost row.

KEY TAKEAWAYS

• Extended ISA comes with notable improvements but is still backward compatible with the ISA boards which allows these boards to take full advantage of this improved bus architecture.
• Since the bus width is wider, the speed of data transfer through this particular bus is theoretically double than that of its predecessor ISA.
• The EISA slots look much similar to the ISA slots but are deeper because a second row of pins has to be accommodated under the ISA pins.
• These slots are however easily distinguishable from the ISA slots due to its brown color and plastic build.
• The high cost of EISA makes it less suitable to use in regular desktop computers and more suitable to use in high-end workstation and server computers.

Understanding Extended Industry Standard Architecture (EISA)

The Extended Industry Standard Architecture was released in September 1988 to use in the IBM compatible computer systems.

It was designed as an upgraded version of original ISA with more improved features so that it could compete with the MCA or Micro Channel Architecture bus.

Though it looks similar to the ISA bus, you can easily distinguish an Extended ISA from it with its brown color plastic.

The high cost of it however does not make it a productive component to use in average desktop computers.

It is best suited for using in server computers and workstations.

With the 16 bits width extended to 32 bits, this bus architecture is usually found in early Pentium computers and on Intel 80386 and 80486 microprocessors.

It was designed by a consortium of nine companies which included:

• Compaq
• AST Research
• Epson
• NEC
• WYSE
• Olivetti
• Hewlett Packard
• Tandy and
• Zenith Data Systems.

Considering the design and performance, the MCA bus architecture offers a slightly better performance over EISA with a speed of 10 MHz as opposed to 8.33 MHz, but the latter provides almost all the benefits that the Micro Channel boasts of. These are:

• Burst mode
• Bus mastering
• 32 bit data and address bus and
• Software configurable assets.

This means that, from the performance point of view you can expect to have similar performance from the Extended ISA. And, all these features are not available in the ISA bus architecture.

However, there are some key features of this specific bus architecture compared to ISA that are worth noting such as:

• The replacement of the monotonous jumper configuration with a much better and seemingly customized software-based configuration and
• The Plug and Play feature which is similar to the standards of the newer systems and automatically allows it to configure the adapter cards.

This bus allows the users to boot into the utility software from a dedicated hard drive partition or even from a floppy disk.

The software would detect every EISA card available in the system and configure several other hardware resources on it or on the system motherboard as available.

These resources can be anything from memory ports to interrupts.

Apart from that, it also allows the users to input information related to the ISA cards used in the system so that the utility software can reconfigure the Extended ISA cards automatically.

This will ensure that there are no resource conflicts.

Characteristics of Extended Industry Standard Architecture

EISA is the bus architecture and is an upgraded version of the 16 bit ISA supporting a 32 bit data path and is designed specifically to share the bus between various Central Processing Units or CPUs.

The unique characteristics of it can be summarized as follows:

• It provides 32 address lines by using a 32 bit data path which helps in accessing 4 GB memory
• It runs at 8 MHz
• It offers a disk based setup for cards and
• The expansion slots in it are twice as deep as those in the ISA slot.

EISA is comparatively costlier than ISA and therefore is used mainly in high end network servers and workstations, as said earlier.

This specific bus is backward compatible with ISA and is certainly not a proprietary bus.

The slot width of EISA is the same as the 16-bit ISA slot but is deeper due to the long fingers of the edge connectors of the 32-bit circuit board in order to connect with the 32-bit pins.

This bus architecture offers an enhanced performance with better and more signals and higher data transfer rates.

It also follows Synchronous Data Transfer Protocol or SDTP to transmit data at a speed of up to 33 MB.

As for the EISA cards, most of these were designed for Small Computer System Interfaces or SCSI and Network Interface Cards or NIC.

It is accessible by a lot of non IBM-compatible computers as well such as MIPS Magnum, SGI Indigo2, HP 9000 and HP Alpha Server.

However, eventually when there was more demand for faster buses in computers these cards were used scarcely making way for some speedier cards such as Video Electronics Standards Association or VESA, Local Bus and others.

Therefore, even with all these features in it, the Extended ISA was never used extensively and is not found in modern computer systems any longer.

ISA vs EISA

• ISA offers 8 or 16 data bits and 24 address bits while EISA offers 32 data bits and address bits
• ISA is asynchronous while EISA is synchronous in nature and performance
• ISA supports 5.55 M/s burst but EISA supports 32M/s sustained burst
• ISA comes with bus master capability but EISA offers full bus master support
• EISA also allows acceptance outside the PC architecture at times unlike ISA
• The memory addressability of ISA is about 1 MB for 8 bits and up to 16 MB for 16 bits but that of EISA is up to 4 GB
• ISA 8 bit and ISA 16 bit support a clock speed of 4.77 MHz and 6 MHz to 8 MHz respectively but EISA support a clock speed of 8.33 MHz
• The data transfer rate of 8 bit ISA and 16 bit ISA are 4.77 MB/s and 16.66 MB/s at 8 MHz but that of EISA is 33.32 MB/s
• The number of pins used in ISA 8 bit and 16 bit are 62 and 98 respectively while in the EISA there is a total of 198 pins with 100 inlay pins out of these and
• The EISA slots are deeper than the ISA slots since there is a second row of pins under the ISA pins.

Moreover, the low cost ISA supports edge triggered TTL IRQs or interrupts with no sharing such as IRQ2, IRQ3, IRQ4, IRQ5, IRQ6, IRQ7, IRQ10, IRQ11, IRQ12, IRQ14, IRQ15.

On the other hand, the high cost EISA bus supports sharable interrupts IRQ0, IRQ1, SRQ2, IRQ3, IRQ4, IRQ5, IRQ6, IRQ7, IRQ8, SRQ9, IRQ10, IRQ11, IRQ12, IRQ13, IRQ14, and IRQ15

Is EISA Compatible with ISA?

Yes it is, especially with the older ISA buses. It is because these buses are backward compatible and have 16-bit superset connectors that support older ISA system boards that have data paths of 8 bits or 16 bits.

In fact, an EISA may even support older XT boards.

Conclusion

The Extended ISA is better than regular ISA in feature and performance and is much similar to the MCA bus architecture.

However, the need for faster buses in modern computers has pushed it out of the picture by the faster VESA and other buses that are now in use.