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Re: call_external for file I/O [message #13213 is a reply to message #13186]

Thu, 22 October 1998 00:00

Charlie Solomon
Messages: 10
Registered: September 1998

Junior Member

Mark Rivers wrote in message ...

> I am not sure what you mean. Is the data actually in a disk file or is it
in
> memory? If it is in a disk file then some process needs to do the disk
I/O.
> If it is in memory then call_external can be used to get it into IDL.

The data is in a disk file initially, the map_file routine puts the relevant
part of the file into memory and sets those pages for sequential access, so
that when IDL accesses the data in memory it is not based on an algorithm
like most recently used. This is optimal for image data in which you may
need to access different subsets of the array at different times.

> Note that IDL's disk I/O on NT is quite fast. >5MB/sec is not hard to
achieve
> using writeu and readu.

I agree that it is fast, but the method we use on our Solaris machine seems
much faster for the same files. I don't have time data available right now,
but I could get it if needed.

Thanks for your reply,
Charlie Solomon
Raytheon Systems Co.

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[Message index]

		Re: call_external for file I/O By: Charlie Solomon on Mon, 26 October 1998 00:00
		Re: call_external for file I/O By: David Foster on Mon, 26 October 1998 00:00
		Re: call_external for file I/O By: Charlie Solomon on Thu, 22 October 1998 00:00
		Re: call_external for file I/O By: rivers on Thu, 22 October 1998 00:00

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