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What is Micro Channel Architecture (MCA)?
Micro Channel Architecture, or MCA, refers to a bus architecture, which is the predecessor of ISA and is designed by IBM. It offers more operational benefits than ISA.
This bus is technically the proprietary 32 bit and 16 bit bus suitable for PS/2 computers that was created to replace the industry standard architecture and smaller AT.
- Micro Channel Architecture was developed by IBM to compete with ISA by offering a 32 bit and 16 bit bus.
- MCA offers several benefits with its useful features, such as address and data parity, interrupt sharing, and more flexible system configuration process, to name a few.
- This bus architecture is not compatible with other bus standards because it comes with smaller pin connections.
Understanding Micro Channel Architecture (MCA)
The MCA bus was introduced by IBM in 1987 and is designed to be a competent rival of the ISA, or Industry Standard Architecture bus, with several additional features.
This specific bus architecture offers useful and additional features, such as:
- A 32-bit bus apart from the regular 16-bit bus
- An automatically configured card, much like Plug and Play
- Bus mastering, which enhances its efficiency.
- I/O data transfers in 16 bit address width and 64 KB address space of 8, 16, 24, or 32 bits
- Memory data transfers in 32 bit address width of 8, 16, 24, or 32 bits within 16 MB or 4 MB address space with 24 bit or 32 bit address width respectively
- Arbitration procedures that support up to 15 devices
- System master to take control of the channel
- A basic transfer process for transferring data between masters and slaves
- Direct Memory Access, which supports multiple DMA channels, allows data transfer in bursts
- Elective streaming data process for faster data transfer
- Address and data parity
- Interrupt sharing
- Flexible system configuration processes with the use of programmable registers
- An adapter interface
- Optional matched-memory extension
- Optional video extension
- Audio signal transfer support
- Exception Condition Reporting Process and
- Electromagnetic characteristics.
The main intention to create MCA by IBM was the setback it experienced in the desktop hardware market segment due to the potential creation of the ISA bus and other trade issues and challenges.
IBM reclaimed its market by recreating the bus architecture and imposing specific licensing requirements.
This improved architecture includes several different aspects, such as:
- An address bus
- An arbitration bus
- A data bus
- A group of interrupt signals and
- Different support signals.
In addition to the above, the improved architecture also allowed transferring data between I/O devices.
Moreover, the memory and control master are based on both synchronous and asynchronous communication.
With all these features added, the new MCA bus upgraded the regular features of the ISA by adding the following:
- Faster speed
- Simpler configuration
- Better power distribution
- Less hardwired systems
- Well-documented standards
- More hardware options
- Higher I/O device addresses and
- More grounding power.
However, the issues with licensing, including the requirement of fees, are considered to be the main factor in the downfall of MCA.
Also, due to the emergence of other competing standards, this bus never became widely popular and was phased out slowly from desktop computers by the mid-1990s.
MCA is not compatible with other bus architectures. The primary reason for this is the smaller pin connections of this bus interface as compared to others.
It was gradually replaced by the ISA bus, which, in turn, was replaced by the PCI, or Peripheral Component Interconnect bus in the mid-1990s.
Advantages of MCA
The different benefits offered by MCA include support for multiple devices that can exist together and share the system bus to interact with each other directly.
The best part is that it supports communications to happen at a much higher speed than CPU and does not need any other system intervention for it.
Other benefits of using a Micro Channel Architecture include:
- POS, or Programmable Option Select support
- Multiple busmaster support
- Enhanced bus arbitration
- Advanced interrupt support and
- Improved grounding.
POS support offered by MCA eliminates the need for juggling between jumpers, as is required in an ISA bus system.
It allows configuring everything with the system software, even in a closed machine.
Multiple busmaster support allows controlling the system bus and sharing it for communication by the devices at a much higher speed.
Arbitration improvement ensures better and higher system output. This is due to more efficient control over the system bus.
Advanced interrupt support allows using level-sensitive interrupts, which enables better management of the system requests in comparison to the dedicated interrupt lines.
This is because there are more possible interrupts due to the sharing of several lines. This eventually results in a more flexible configuration, reduced chances of lost interrupts, and a more stable system.
On the other hand, improved grounding helps in eliminating system crashes due to better handling of unnecessary signals by an adapter board.
For a user, all these benefits mean an easily configured and more stable system, allowing easy installation of option boards and running software setup.
As for the high-end systems, these benefits offered by MCA offer greater I/O speed, which is theoretically 66 MB/sec at its maximum, which is double the speed offered by EISA.
In addition, the optimal block transfer size is twice that of Enhanced ISA, at 2 KB.
The only disadvantage of the MCA bus is that it belongs to IBM and therefore cannot be easily licensed as EISA. Also, as for the MCA memory boards, there can be a loss of about 20 to 25% in the output in the system board memory.
However, in reality, the impact on the work may not be incredibly extensive or visible, depending on the tasks performed.
As you can see, the Micro Channel Architecture of IBM offers a lot of benefits with its useful features.
However, it is the specific downsides of it related to licensing issues and incompatibility due to the smaller pins that resulted in its fall from favor and being replaced by ISA first and then by PCI.