National Instruments GPIB-PC - Manual (Page 240)

Differences Between Software Revisions Appendix C
GPIB-PC User Manual C-2 ©National Instruments Corp.
New Functions
File I/O functions have been added to the handler, allowing data to be
read into or written from a file. In Interpretive BASIC, integer I/O
functions have been added to allow the data to be stored in integer
arrays instead of character strings.
Modified Functions
IBFIND no longer uses up available DOS file descriptors, so the Too
Many Files error will not occur as a result of too many open boards
and devices. IBONL , when called with a 0, no longer invalidates the
unit descriptor. It still disables the board or device, however.
Language Interfaces
If you customized a language interface for a compiler not supported in
Rev. B, it will need to be modified to work with Rev. C. This is
because Rev. C language interfaces use a new, faster method of
entering the handler.
General
The Rev. C software package as a whole has been modified to allow it
to run with a variety of GPIB-PC cards and systems.
Revision C and Revision D
Both Rev. C and Rev. D software are current and are actively supported.
The one you receive depends on the GPIB-PC interface hardware you
buy.
Device Functions
Device I/O functions do not unaddress devices at the end of the call.
Also, the functions do not address devices known to be already
addressed from the previous call. This significantly improves through-
put on multiple reads from or multiple writes to the same device.
Also in Rev. D, if the access board is not CIC when a device call is
made, the ECIC error is returned.
Non-Interrupt Mode
Rev. D has no non-interrupt mode. You must select interrupt level 2-7.