MCA Benefits
ISA Static Grounding

   The PC and AT board bracket is designed to be grounded to the chassis ground via the mounting screw. If the mounting screw is loose or missing, then there is no straight path to ground. If the mounting bracket is not electrically isolated, then there are only the 3 pins on the PC Bus, which were intended only to provide a logic reference, to ground the static.
   If the mounting screw is not tight, static may go to ground through the card circuitry, possibly causing data alteration. Also, the mounting screw does not guarentee that the card is actually centered in the slot.
   The design of the PC/AT bus is quite simple, with only three ground lines in either design.On the motherboard, the shielding is adequate, but once the signals rise up into the adapters, the shielding is much less and the signals radiate more.Testing puts the limit to the PC/AT bus around 30-34 MHz due to generated interference.

MCA Static Grounding

   The MCA grounding and mounting scheme eliminates the problems of the ISA bracket. The MCA slot bracket has several spring fingers to maintain positive contact with the sides of the slot. The metal bracket blocks radiation that would otherwise leak from the slot. It is electrically isolated from the card circuitry, thus reducing the possibility of data alteration.
   Instead of depending on a mounting screw at the top, the mounting bracket actually fits inside of a frame that is at the rear of the system, and this provides positive centering of the adapter.In addition, the V-shaped slot at the bottom of the MCA slot bracket fits around a knurled thumbscrew, ensuring a tight fit.
   The MCA bus is laid out with every fourth pin on each side of the connector either power or ground. Since the power connection offers about the same shielding ability as a ground, every signal is within 1/10th of an inch or less of a shielding lead. This allows an upper operating frequency nearly three times that of the PC bus.

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