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What is DMA structure?
Using interrupts driven device drivers to transfer data to or from hardware devices works well when the amount of data is reasonably low. For example a 9600 baud modem can transfer approximately one character every millisecond ( 'th second). If the interrupt latency, the amount of time that it takes between the hardware device raising the interrupt and the device driver's interrupt handling routine being called, is low (say 2 milliseconds) then the overall system impact of the data transfer is very low. The 9600 baud modem data transfer would only take 0.002% of the CPU's processing time. For high speed devices, such as hard disk controllers or ethernet devices the data transfer rate is a lot higher. A SCSI device can transfer up to 40 Mbytes of information per second. Direct Memory Access, or DMA, was invented to solve this problem. A DMA controller allows devices to transfer data to or from the system's memory without the intervention of the processor. A PC's ISA DMA controller has 8 DMA channels of which 7 are available for use by the device drivers. Each DMA channel has associated with it a 16 bit address register and a 16 bit count register. To initiate a data transfer the device driver sets up the DMA channel's address and count registers together with the direction of the data transfer, read or write. It then tells the device that it may start the DMA when it wishes. When the transfer is complete the device interrupts the PC. Whilst the transfer is taking place the CPU is free to do other things. Device drivers have to be careful when using DMA. First of all the DMA controller knows nothing of virtual memory, it only has access to the physical memory in the system. Therefore the memory that is being DMA'd to or from must be a contiguous block of physical memory. This means that you cannot DMA directly into the virtual address space of a process. You can however lock the processes physical pages into memory, preventing them from being swapped out to the swap device during a DMA operation. Secondly, the DMA controller cannot access the whole of physical memory. The DMA channel's address register represents the first 16 bits of the DMA address, the next 8 bits come from the page register. This means that DMA requests are limited to the bottom 16 Mbytes of memory. DMA channels are scarse resources, there are only 7 of them, and they cannot be shared between device drivers. Just like interrupts the device driver must be able to work out which DMA channel it should use. Like interrupts, some devices have a fixed DMA channel. The floppy device, for example, always uses DMA channel 2. Sometimes the DMA channel for a device can be set by jumpers, a number of ethernet devices use this technique. The more flexible devices can be told (via their CSRs) which DMA channels to use and, in this case, the device driver can simple pick a free DMA channel to use. Linux tracks the usage of the DMA channels using a vector of dma_chan data structures (one per DMA channel). The dma_chan data structure contains just two fields, a pointer to a string describing the owner of the DMA channel and a flag indicating if the DMA channel is allocated or not. It is this vector of dma_chan data structures that is printed when you cat /proc/dma
Which program facilitates communication between device and OS?
Usually a device driver facilitates communication between a device and the OS. Device drivers are written in low-level languages such as Assembly or C.
Red X from toolbar?
This can sometimes occur when your computer's system resources are low (low physical memory or near-full page file).
What is the transmission protocol between a computer and a peripheral device?
The way a computer communicates with a peripheral device is through a device driver. A device driver is a low level computer program that allows higher level programs to communicate with a hardware device connected to the computer bus. Device drivers are hardware dependent and specific to an operating system.
What are the technical specifications of a solid state hard drive?
A solid state hard drive is a data storage device. It is designed to replace a mechanical hard disk, but does not contain any moving parts, storing data on flash memory chips. They differ from flash drives in that they are not designed to be removable, and are designed for speed, and not for low cost.
How does one troubleshoot a problem with windows virtual memory minimum being too low?
If a person is getting a message that says they are running low on virtual memory from their pc, it usually means that Windows isn't managing the memory correctly. If the virtual memory minimum is too low, then a person can go into the system and edit the amount of virtual memory manually which should fix the problem.
What solution could be determined to resolve low virtual memory minimum?
The solution to resolving low virtual memory is two part, part one is increasing the physical memory in the machine (RAM). If one can't increase the physical memory then one can increase the page file size. If neither of these work, then there is probably a application that is corrupt on the machine and needs addressing.
What is defined as the condition that occurs when your system is running out of virtual memory?
When a PC runs low on virtual memory, system activity causes what is called "thrashing", when memory is repeatedly paged out to, and read back from, the hard drive.
How does virtual memory work in XP?
Virtual Memory is like RAM but XP put's it on you hard drive for extra space. I had a problem when I played certain games on XP that it stopped the game and a window popped up and said "virtual memory too low." If you have a problem like this you can always change the maximum amount allowed. WARNING: Do not change the minimum amount unless you know what you are doing. Do not modify your maximum amount larger than you free space. And remember to leave room for other applications to be installed, etc.
What do you need to do when virtual memory low comes up in botton right hand corner of your computer?
more RAM
We have been getting a warning on your comp about our virtual memory being low how does this happen and how do we fix it?
You need to delete some programs or buy a new ram card to make memory bigger!
Tcp ip protocol stack reported that it ran out of memory?
main cause is spyware or malware or virus - scan and delete the virus\worm\spy sometime it happen due to low memory - increase virtual memory
What is thrashing and how it will be overcome?
when there are too many processes available and memory is low, than processor remains busy in swapping in and out the pages from disk in order to overcome it: 1) increase memory 2) reduce multi programming level
What is the minimum price for voice mail systems?
The cost of a voicemail system will depend on what brand the system is and features included. However, there are some virtual voicemail systems for as low as $20.
Witch player use to low memory for 256mb?
aimp2 is used to low memory for all computer including low ram memory
What would you need to shot a low budget independent film?
You need a script, a camera, some actors, and a decent audio device. That's really your bare minimum. :)
How does c give access to low level memory?
Define 'low level memory' first.
