RE: Weirdest thing ever

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Well I didn't expected it to work beyond 4 Gb. I already tested it and it works with a database file of about 3 Gb, so data access is possible and that's good enough (in 15 years it has grown to almost 2gb and in less than a year we plan to migrate to another solution, so it will do).

Seeing that in the test server it's working without problems with a 64 bits CentOS we've decided delete the fedora installation and install CentOS, so I won't worry looking more into it.

-----Mensaje original-----
De: Paul Crawford [mailto:psc@xxxxxxxxxxxxxxxx] 
Enviado el: viernes, 28 de enero de 2011 14:13
Para: Xavier Tarifa
CC: linux-msdos@xxxxxxxxxxxxxxx
Asunto: Re: Weirdest thing ever

Dear Xavier,
> While it is conceivable that a DOS program could read beyond 2GB, it 
> is very unlikely it could seek to those positions, and very certain it 
> could not do so beyond 4GB.

Just to say that in the course of other testing here, I looked to see what the Microsoft C6.0 library calls for filelength() did with 64-bit dosemu. What I found was:

With 32-bit Linux/dosemu it can't open files >2GB.

With 64-bit it can open files >2GB but sees the length incorrectly:

For <4GB it is correct if you treat the returned value as unsigned. This may be the case in some software, but it is unlikely to be universal.

For files >4GB it seems to only get the lower 32-bits of the size, so the file appears (incorrectly) to be less than 4GB in size. I would have prefered the system to return (4GB-1) as at least you know the file is very big in this case!

However, I have not tested to see if useful data access is possible >2GB as I don't have any DOS applications that use very large files.

Dr. Paul S. Crawford
Satellite Station
Dundee University
Small's Wynd, Dundee,
DD1 4HN, U.K.
Tel: +44 (0)1382 38 4687
Email: psc@xxxxxxxxxxxxxxxx
The University of Dundee is a Scottish Registered Charity, No. SC015096
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