Direct memory access (DMA) :-
it is a method that allows an input/output (I/O) device to send or receive data
directly to or from the main memory, by passing the CPU to speed up
memory operations. The process is managed by a chip known as a DMA
controller (DMAC).
In older computers, four DMA channels were numbered 0, 1, 2 and 3.When
the16-bit industry standard architecture (ISA) expansion bus was introduced,
channels 5, 6 and 7 were added. ISA was a computer bus standard for IBM-
compatible computers, allowing a device to initiate transactions (bus
mastering) at a quicker speed. ISA has since been replaced by accelerated
graphics port (AGP) and peripheral component interconnect (PCI) expansion
cards, which are much faster. Each DMA transfers approximately 2 MB of
data per second.
A computer's system resource tools are used for communication between
hardware and software. The four types of system resources are:
•I/O addresses
•Memory addresses
•Interrupt request numbers (IRQ)
•Direct memory access (DMA) channels
Slow devices like keyboards will generate an interrupt to the main CPU after
each byte is transferred. If a fast device such as a disk generated an interrupt
for each byte, the operating system would spend most of its time handling
these interrupts. So a typical computer uses direct memory access (DMA)
hardware to reduce this overhead.
Direct Memory Access (DMA) means CPU grants I/O module authority to
read from or write to memory without involvement. DMA module itself
controls exchange of data between main memory and the I/O device. CPU is
only involved at the beginning and end of the transfer and interrupted only
after entire block has been transferred.
, Direct Memory Access needs a special hardware called DMA controller
(DMAC) that manages the data transfers and arbitrates access to the system
bus. The controllers are programmed with source and destination pointers
(where to read/write the data), counters to track the number of transferred
bytes, and settings, which includes I/O and memory types, interrupts and
states for the CPU cycles.
DMA channels are used to communicate data between the peripheral device
and the system memory. All four system resources rely on certain lines on a
bus. Some lines on the bus are used for IRQs, some for addresses (the I/O
addresses and the memory address) and some for DMA channels.
A DMA channel enables a device to transfer data without exposing the CPU
to a work overload. Without the DMA channels, the CPU copies every piece
of data using a peripheral bus from the I/O device. Using a peripheral bus
occupies the CPU during the read/write process and does not allow other
work to be performed until the operation is completed.
With DMA, the CPU can process other tasks while data transfer is being
performed. The transfer of data is first initiated by the CPU. During the
transfer of data between the DMA channel and I/O device, the CPU
performs other tasks. When the data transfer is complete, the CPU receives
an interrupt request from the DMA controller.
In the Direct Memory Access (DMA) the interface transfer the data into and
out of the memory unit through the memory bus. The transfer of data
it is a method that allows an input/output (I/O) device to send or receive data
directly to or from the main memory, by passing the CPU to speed up
memory operations. The process is managed by a chip known as a DMA
controller (DMAC).
In older computers, four DMA channels were numbered 0, 1, 2 and 3.When
the16-bit industry standard architecture (ISA) expansion bus was introduced,
channels 5, 6 and 7 were added. ISA was a computer bus standard for IBM-
compatible computers, allowing a device to initiate transactions (bus
mastering) at a quicker speed. ISA has since been replaced by accelerated
graphics port (AGP) and peripheral component interconnect (PCI) expansion
cards, which are much faster. Each DMA transfers approximately 2 MB of
data per second.
A computer's system resource tools are used for communication between
hardware and software. The four types of system resources are:
•I/O addresses
•Memory addresses
•Interrupt request numbers (IRQ)
•Direct memory access (DMA) channels
Slow devices like keyboards will generate an interrupt to the main CPU after
each byte is transferred. If a fast device such as a disk generated an interrupt
for each byte, the operating system would spend most of its time handling
these interrupts. So a typical computer uses direct memory access (DMA)
hardware to reduce this overhead.
Direct Memory Access (DMA) means CPU grants I/O module authority to
read from or write to memory without involvement. DMA module itself
controls exchange of data between main memory and the I/O device. CPU is
only involved at the beginning and end of the transfer and interrupted only
after entire block has been transferred.
, Direct Memory Access needs a special hardware called DMA controller
(DMAC) that manages the data transfers and arbitrates access to the system
bus. The controllers are programmed with source and destination pointers
(where to read/write the data), counters to track the number of transferred
bytes, and settings, which includes I/O and memory types, interrupts and
states for the CPU cycles.
DMA channels are used to communicate data between the peripheral device
and the system memory. All four system resources rely on certain lines on a
bus. Some lines on the bus are used for IRQs, some for addresses (the I/O
addresses and the memory address) and some for DMA channels.
A DMA channel enables a device to transfer data without exposing the CPU
to a work overload. Without the DMA channels, the CPU copies every piece
of data using a peripheral bus from the I/O device. Using a peripheral bus
occupies the CPU during the read/write process and does not allow other
work to be performed until the operation is completed.
With DMA, the CPU can process other tasks while data transfer is being
performed. The transfer of data is first initiated by the CPU. During the
transfer of data between the DMA channel and I/O device, the CPU
performs other tasks. When the data transfer is complete, the CPU receives
an interrupt request from the DMA controller.
In the Direct Memory Access (DMA) the interface transfer the data into and
out of the memory unit through the memory bus. The transfer of data
