Welcome to Linux Knowledge Base and Tutorial
"The place where you learn linux"
Karen Lilly Creations

 Create an AccountHome | Submit News | Your Account  

Tutorial Menu
Linux Tutorial Home
Table of Contents
Up to --> The Computer Itself

· The Expansion Bus
· Industry Standard Architecture ISA
· MCA
· Extended Industry Standard Architecture EISA
· The Small Computer Systems Interface SCSI
· Termination
· PCI
· AGP

Glossary
MoreInfo
Man Pages
Linux Topics
Test Your Knowledge

Site Menu
Site Map
FAQ
Copyright Info
Terms of Use
Privacy Info
Disclaimer
WorkBoard
Thanks
Donations
Advertising
Masthead / Impressum
Your Account

Communication
Feedback
Forums
Private Messages
Recommend Us
Surveys

Features
HOWTOs
News
News Archive
Submit News
Topics
User Articles
Web Links

Google
Google


The Web
linux-tutorial.info

Who's Online
There are currently, 182 guest(s) and 0 member(s) that are online.

You are an Anonymous user. You can register for free by clicking here

  
Linux Tutorial - The Computer Itself - The Expansion Bus - MCA
  Industry Standard Architecture ISA ---- Extended Industry Standard Architecture EISA  


MCA

The introduction of IBM's Micro-Channel Architecture (MCA) was a redesign of the entire bus architecture. Although IBM developed the original AT architecture, which later became ISA, many companies produced machines that followed this standard. The introduction of MCA meant that IBM could produce machines to which it alone had the patent rights.

One of the most obvious differences is the smaller slots required for MCA cards. ISA cards are 4.75 x 13.5 inches, compared with the 3.5 x 11.5-inch MCA cards. As a result, the same number of cards can fit into a smaller area. The drawback was that ISA cards could not fit into MCA slots, and MCA cards could not fit into ISA slots. Although this might seem as though IBM had decided to cut its own throat, the changes they made in creating MCA made it very appealing.

Part of the decrease in size was a result of surface mount components, or surface mount technology (SMT). Previously, cards used "through-hole" mounting, in which holes were drilled through the system board (hence the name). Chips were mounted in these holes or into holders that were mounted in the holes. Surface mount does not use this and as a result, looks "flattened" by comparison. This saves not only space but also time and money, as SMT cards are easier to produce. In addition, the spacing between the pins on the card (0.050") corresponds to the spacing on the chips, which makes designing the boards much easier.

Micro-Channel also increases speed because there is a ground on every fourth pin, which reduces interference, and as a result, the MCA-Bus can operate at ten times the speed of non-MCA machines and still comply with FCC regulations in terms of radio frequency interference.

Another major improvement was the expansion of the data bus to 32 bits. This meant that machines were no longer limited to 16 megabytes of memory, but could now access 4 gigabytes.

One key change in the MCA architecture was the concept of hardware-mediated bus arbitration. With ISA machines, devices could share the bus, and the OS was required to arbitrate who got a turn. With MCA, that arbitration is done at the hardware level, freeing the OS to work on other things. This also enables multiple processors to use the bus. To implement this, the bus has several new lines. Four lines determine the arbitration bus priority level, which represents the 16 different priority levels that a device could have. Who gets the bus depends on the priority.

From the users perspective, the installation of MCA cards is much easier than that of ISA cards due to the introduction of the Programmable Option Select, or POS. With POS, the entire hardware configuration is stored in the CMOS. When new cards are added, you are required to run the machines reference disk. In addition, each card comes with an options disk that contains configuration information for the card. With the combination of reference disk and options disk, conflicts are all but eliminated.

Part of the MCA spec is that each card has its own unique identifying number encoded into the firmware. When the system boots, the settings in the CMOS are compared to the cards that are found on the bus. If one has been added or removed, the system requires you to boot using the reference disk to ensure that things are set up correctly.

As I mentioned, on each options disk is the necessary configuration information. This information is contained within the Adapter Description File (ADF). The ADF contains all the necessary information for your system to recognize the expansion card. Because it is only a few kilobytes big, many ADF files can be stored on a floppy. This is useful in situations like those we had in tech support. There were several MCA machines in the department with dozens of expansion cards, each with its own ADF file. Rather than having copies of each disk, the analysts who supported MCA machines (myself included) each had a single disk with all the ADF files. (Eventually that, too, became burdensome, so we copied the ADF files into a central directory where we could copy them as needed.) Any time we needed to add a new card to our machines for testing, we didn't need to worry about the ADF files because they were all in one place.

Because each device has its own identification number and this number is stored in the ADF, the reference diskette can find the appropriate number with no problem. All ADF files have names such as @BFDF.ADF, so it isn't obvious what kind of card the ADF file is for just by looking at the name. However, because the ADF files are simply text files, you can easily figure out which file is which by looking at the contents.

Unlike ISA machines, the MCA architecture enables interrupt sharing. Because many expansion boards are limited to a small range of interrupts, it is often difficult, if not impossible, to configure every combination on your system. Interrupt sharing is possible on MCA machines because they use something called level-triggered interrupts, or level-sensitive interrupts.

With edge-triggered interrupts, or edge-sensitive interrupts, (the standard on ISA buses), an interrupt is generated and then is dropped. This sets a flag in the PIC, which figures out which device generated the interrupt and services it. If interrupts were shared with edge-triggered interrupts, any interrupt that arrived between the time the first interrupt is generated and serviced would be lost because the PIC has no means of knowing that a second interrupt occurred. All the PIC sees is that an interrupt occurred. Figure 0-2 shows how each of these elements relate to each other in time.

Figure - Interrupt Signal(Interactive)

With level-triggered interrupts, when an interrupt is generated, it is held high until the PIC forces it low after the interrupt has been serviced. If another device were on the same interrupt, the PIC would try to pull down the interrupt line; however, the second device would keep it high. The PIC would then see that it was high and would be able to service the second device.

Despite the many obvious advantages of the MCA, there are a few drawbacks. One primary drawback is the interchangeability of expansion cards between architectures. MCA cards can only fit in MCA machines. However, it is possible to use an ISA card in an EISA machine, and EISA machines is what I will talk about next.

 Previous Page
Industry Standard Architecture ISA
  Back to Top
Table of Contents
Next Page 
Extended Industry Standard Architecture EISA


MoreInfo

Test Your Knowledge

User Comments:


You can only add comments if you are logged in.

Copyright 2002-2009 by James Mohr. Licensed under modified GNU Free Documentation License (Portions of this material originally published by Prentice Hall, Pearson Education, Inc). See here for details. All rights reserved.
  

The Linux Tutorial is always looking for new contributors.


Login
Nickname

Password

Security Code
Security Code
Type Security Code


Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.

Help if you can!


Amazon Wish List

Did You Know?
You can help in many different ways.


Friends



Tell a Friend About Us

Bookmark and Share



Web site powered by PHP-Nuke

Is this information useful? At the very least you can help by spreading the word to your favorite newsgroups, mailing lists and forums.
All logos and trademarks in this site are property of their respective owner. The comments are property of their posters. Articles are the property of their respective owners. Unless otherwise stated in the body of the article, article content (C) 1994-2013 by James Mohr. All rights reserved. The stylized page/paper, as well as the terms "The Linux Tutorial", "The Linux Server Tutorial", "The Linux Knowledge Base and Tutorial" and "The place where you learn Linux" are service marks of James Mohr. All rights reserved.
The Linux Knowledge Base and Tutorial may contain links to sites on the Internet, which are owned and operated by third parties. The Linux Tutorial is not responsible for the content of any such third-party site. By viewing/utilizing this web site, you have agreed to our disclaimer, terms of use and privacy policy. Use of automated download software ("harvesters") such as wget, httrack, etc. causes the site to quickly exceed its bandwidth limitation and are therefore expressly prohibited. For more details on this, take a look here

PHP-Nuke Copyright © 2004 by Francisco Burzi. This is free software, and you may redistribute it under the GPL. PHP-Nuke comes with absolutely no warranty, for details, see the license.
Page Generation: 0.06 Seconds