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Where or what documentation did you read the phrase "DAC 40/1024?"
What is part number of the component to which the phrase refers?
As both milind.a.kulkarni and rhaynes mentioned 1024 most likely refers to a Digital to Analog Converter with 10 bits of resolution, 40 could represent the maximum sample rate in either kilo or mega samples/sec, KSPS or MSPS.
Specifying the document or URL which you found the phrase, "DAC 40/1024" would provide a more definitive answer.