Technical information

SEGA Confidential

1.0 Overview of CD Emulation

1.1 Summary of VCD Emulator Functions

The VCD emulator is an MS-DOS program that runs on PC-compatible computers.

By communicating with the VCD I/F Board inserted into the expansion slot of a PC

compatible, the emulator receives CD access instructions sent from the target box,

accesses MS-DOS files according to the instructions, and emulates access to the CD

drive.

The following list summarizes the VCD emulator functions:

• MS-DOS file data Virtual CD playback emulation

• Game-CD disk image production

• Game-CD disk image Virtual CD playback emulation

• Disk image partial update playback emulation

• TOC file production for write-once CD creation

• Error simulation

• History log display of communications between the VCD emulator and CD Block

- Commands and status received

- Process result (error) message

- Selection of communication content display (error only, all)

• Display of TOC data

• Display of relational data

- File location relationship of the CD disk image and the MS-DOS files used to create the image.

MS-DOS files can be accessed in three formats: as collections of data files before

they become CD images; as files containing unaltered CD images; and as partially

revised CD images and data files.

Collections of Data Files Before they Become a CD Image

The data from these MS-DOS files (hereafter called data files) are used to create CD

images. The VCD emulator examines the file according to the access position of the

CD access command received from the VCD I/F Board, edits the data to emulate a

CD image, and sends the result to the VCD I/F Board. This process allows the target

box to receive the data in the same form as it would be input from the CD drive. This

is called “Direct DOS File Access” emulation mode. This emulation can be started

with simple preprocessing as long as the data for creating the CD image has already

been prepared. However, because the data is sent as it is being edited, it cannot be

played back with the same timing as that of the data input from the actual CD drive.

Therefore, the MPEG playback and channel interleave (described later) that requires

complex disc access cannot be supported in this emulation mode.