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Electralogics -- Quasi-Disk
This board was Electralogics best known board.  It came out at a time (1983) when dynamic RAM prices had come down to a point where memory disks started to make sense. 


The disk also had a piggy-back second board which connected via a two sockets and four screws to the S-100 board. It was a tight fit in the S-100 bus not to loose a card slot.

Daughter board

The board was fully S-100 696 compatible  but would work in many older systems as well. The board could be configured with 64K or 256K dynamic RAM chips giving a maximum capacity of 4 Megabytes of RAM.  There was software error detection and DMA transfer capability up to 2 megabytes/second.   There also was on-board power-fail logic to write protect the disk during brownouts or power failures to prevent accidental destruction of data.

You could also add an optional battery backup option which provided protection for about 2 hours.  This option included battery charging logic, circuitry to prevent accidental battery damage which may result from "deep discharge" as well as a power supply to support the data when the host system is turned off.

The PC board itself was a six layered board to improve performance and reliability by reducing board noise levels.  The board required 6 I/O ports to operate. 80H-86H was the default block of ports.  The board accepted extended addressing (i.e. I/O address lines A0-A15). It had an on-board 22 bit address generator that could be programmed for auto increment or decrement if desired thereby speeding things up.

Any sector size could be implemented. Burst transfers of up to 4 megabytes of data (or entire board capacity) were possible because the entire 22 bit address was incremented/decremented as programmed on each data access.

My only criticism of the board is that when fully loaded with RAM the voltage regulator really runs hot. The board is particularly sensitive to the S-100 +8 line. Most 5V voltage regulators on S-100 boards run fine at 7.0V (from a switching power supply) on the bus and so generate little heat.  This board will trigger a power fail if the voltage goes below 7.5 volts.
The manual for this board can be obtained here.
The schematic for this board can be obtained here.
A device driver (MDSIK.zip) for CPM V3.0 I wrote for this disk can be obtained here.


Other Electralogics S-100 Boards
Quasi-Disk   64K RAM    MFIO Board


This page was last modified on 10/25/2013