Information Regarding Buffered I/O and MSCDEX

• Microsoft Software Development Kit (SDK) for Windows version 3.0

SUMMARY

In the Microsoft Multimedia Windows environment, the MSCDEX driver provides buffered input and output (I/O) from the CD-ROM device. The information below discusses using buffered I/O in an application.

MORE INFORMATION

When 32K of data is read from the disk in response to a request from an application, 32K additional data is read from the disk into a buffer in anticipation of another sequential read request.

Currently, all information read from the CD-ROM is in response to a synchronous MS-DOS file I/O request. This prevents an application from requesting that a particular portion of data be read from the disk while the application performs some other processing. Although an implementation of asynchronous I/O is being researched, it will not be implemented soon. It would be necessary to rewrite all CD-ROM drivers currently in use to implement asynchronous I/O.

To fill the buffer with an arbitrary selection from the CD-ROM, an application can request one byte of data from the beginning of the selection to be read. After the CD-ROM seeks to the data and reads one byte, control is returned. The driver reads the remainder of the data into the buffer asynchronously.