The document discusses direct memory access (DMA) and DMA controllers. It explains that DMA allows hardware subsystems like disk drives and graphics cards to access main memory independently of the CPU. This is useful because it allows data transfers to occur in parallel with other CPU operations, improving overall system performance. A DMA controller generates memory addresses and initiates read/write cycles. It has registers that specify the I/O port, transfer direction, and number of bytes to transfer per burst. DMA controllers use different transfer modes like burst, cycle stealing, and transparent to move blocks of data efficiently between peripheral devices and memory.

1.  Introduction to the DMA and DMA controller.
 Need of DMA and DMA controller.
 Working of the DMA and DMA controller.

2. What is DMA ?
 DMA represents the DIRECT MEMORY
ACCESS. Means there is a direct way to access
the memory not by the help of other device.
 DMA is a feature of computerized system that
allows the certain hardware subsystems to
access main memory independently of CPU.

3.  Without DMA ,during input/output operation the
whole CPU is occupied for read and write operation
, and is thus unavailable to perform other work.
 With DMA , the CPU does the other operation while
the transfer is in progress.
 DMA is used in intra-chip data transfer in multi-
core processors and also used in disk drive ,
graphic cards, network cards and sound cards.

4.  A DMA controller can generate memory
addresses and initiate memory read or write
cycles.
 It contains several processor registers that
can be written and read by the CPU.
 The control registers specify the I/O port to
use , the direction of the transfer and the
number of bytes to transfer in one burst.

5. An entire block of
data is transferred in
one contiguous
sequence.
Once the DMA
controller is granted
access to the
system bus by the
CPU, it transfers all
bytes of data in the
data block .
Burst Mode Cycle Stealing mode
The cycle stealing
mode is used in
systems in which
the CPU should not
be disabled for the
length of time
needed for burst
transfer modes.
In the Cycle stealing
mode , the DMA
controller obtains
access to the system
bus.
Transparent mode
The transparent
mode takes the
most time to
transfer a block of
data , yet it is also
the most efficient
mode in terms of
overall System
performance.

6. Micro
Processor
Memory
DMA
Controller
Peripheral
Device
Address bus
Data bus
Control bus
Hold
Ack
Hold
Reque
st
Data bus
Control
DMA Request
DMA Ack