ADLINK PCI-9810 - Manual (Page 53)

Operation Theory 41
Storing data from the host memory to a hard disk or other storage
devices must also be considered. The burst data rate of current
HDD technology could be between 90 and 80 MB/s. However in
reality, the effective bandwidth of a HDD is usually less than 10
MB/s, especially when the HDD seek time is longer. For example,
if the HDD seek time is 20 ms, the FIFO is already full and the
acquired data cannot be continuous.
Several limitations may be due to the OS and host memory size.
In DOS, the maximum allocated memory size is less than 640K,
except when you use an extended memory managing software. In
Windows 95 or Windows NT, it is relatively difficult to get a
continuously large memory size such as 64 MB. It is possible to
allocate a large memory size by keeping the memory clean. The
PCI bus-mastering DMA controller of the PCI-9812 needs
continuous memory to store the AD data.