Morrow - HDC-DMA
Hard Disk Controller
This was another well designed S-100 Hard disk controller board.
This Hard Disk/Direct Memory Access (HDCDMA) Hard Disk
Controller is a single board S-100 bus subsystem. It can communicate with up
to four 5 1/4 inch or four 8" hard disks. The HDCDMA will support a mixture
of types of drives, but all must have the same transfer rate. Variable
designs, capacities and sector formats are possible for each type of drive,
allowing users to upgrade their systems with new drives as they become
The HDCDMA is an intelligent controller. The
arrangement of data on the disk is not limited by a special purpose LSI
controller chip. This allows system designers the freedom to specify sector
sizes and interleave to fit the requirements of special applications.
The controller has its own 8X300 bipolar microprocessor
operating at 7.16 megahertz which is used to supervise data transfers
between disk drives and memory without the intervention of the main CPU.
This relieves the main CPU of time consuming processes which include head
positioning, rotational delays and the usual byte-by-byte transfer of data
from the controller to main memory. As a result, transfers are faster and
more efficient. Moreover, the main CPU has more time for data processing,
and thus, supports more users and/or tasks.
The main advantage of the HDCDMA controller over almost
all the others is its glitch free direct memory access channel. This
advanced "channel" concept allows the controller to communicate with S-100
memory by "stealing" bus cycles from the main CPU, or using the bus in
"burst mode" for ultra-fast data transfer. This idea of an intelligent I/O
channel was first implemented by IBM on their famous 370 mainframes. Now,
this powerful concept has been implemented on the S-100 bus.
The channel has the full 24-bits of memory addressing
as described in the proposed IEEE standard for the S-100 bus. Also, a great
deal of care has been taken in the design of the interface circuitry so that
it conforms in every detail to this new standard and still allows the
controller to work well with existing systems designed before the
standardization effort was started.
The board has priority logic which allows it to contend
with up to 15 other "temporary masters" which may also want to "steal" bus
cycles from the main CPU (the permanent master).
The features associated with the intelligent channel on
the controller make it especially desirable in multi-tasking and multi-user
applications. In fact, many were tailored to enhance the performance of
Morrow Designs new, powerful DECISION I multiprocessing IEEE 696/S-100
machine. DMA style controllers are an integral part of advanced
microcomputer systems which incorporate many of the concepts previously
supported only on mainframe systems, such as the IBM 370 series.
The manual for this board can be
here for some fine adjustments often need with this board.
Morrow S-100 Boards
Disk Jockey FDC
Hard Disk Controller
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