Specifications
CD-i FAQ 2000 Edition Revised February 21, 2001
Latest version and more CD-i info: http://www.icdia.org
15
3. CD-i Techniques
3.1 What are CD-i's basic specs?
A CD-i player is based on a 68000 CPU running at least at 15 MHz, it is equiped with at least 1
MB of RAM, a single speed CD-drive, dedicated audio and video decoding chips, at least 8 KB of
non-volatile storage memory and a dedicated operating system called CD-RTOS. The minimal
specifications to which every CD-i player should comply are laid down in the Green Book, which
is covered in full detail in section 1 of this FAQ. A CD-i player can have extended hardware (such
as more RAM or more non-volatile storage space), as long as the minimum requirements of the
Green Book are met.
3.2 What CPU does CD-i use?
A CD-i player is equiped with a Motorola 68000-like processor, similar to the ones used in the
original Apple Macintosh, Atari ST and Commodore Amiga. All Philips CD-i players used a
Philips-build 68070, which differs from the 68000 in that way that it had some port controlling
features build in. The processor runs at 15 MHz. According to the Green Book, the 68000-CPU
should at least have a 16 bit external data path, and a 32 bit internal data path, very similar to
Intel's 80386SX processor. The CD-i standard allows for a faster CPU, but since CD-i's
performance is almost entirely based on the realtime retrieval of audio and video data from the
disc, the performance will not be raised that much when a faster CPU is used. This is why CPUs
in all CD-i players build to date are based on the minimal Green Book requirements.
3.3 What OS does CD-i use?
The operating system used in a CD-i player is called CD-RTOS, which stands for Compact Disc
Real-Time Operating System. It is hard coded in a ROM of at least 512 KB, along with other
player-specific software such as the player's startup shell. CD-RTOS is based on version 2.4 of
Microware's OS-9/68K operating system. OS-9 is very similar to Unix, and supports full
multitasking and multi-user operation. The original OS-9 was build in the early 80s as a realtime
operating system to be used in industrial and embedded applications were real time functionality
is a key criteria, such as with robotics, automobile production and set-top boxes. It was slightly
adapted to CD-i, for example by including the correct device descriptors for the CD drive, and
with drivers for CD-i's specific audio and video decoding ICs. Since OS-9 is a modular operating
system with a very small kernel of only about 25 KB, only the parts used by a specific CD-i player
have to be preset in ROM. For example, a CD-i player with a floppy disk drive contains additional
driver modules, whereas most consumer players do not need them.
3.4 What's a real-time system?
A real-time computer system is a system in which the timing of events plays a critical role in the
operation. For example, in the robotics area, where OS-9 is also extensively used, it is of great
importance that different tasks occure at the exact specified moment. In CD-i, real-time behaviour
is also important, since audio and video data need to be decoded by the appropriate processors
and then send to the appropriate outputs. At the same time, the system should take care of user
input.
3.5 What's sector interleaving?
One of the clever design creteria of CD-i was that the system should be able to retreive audio and
video information in realtime from the disc and send this information directly to the appropriate
decoder ICs, without putting a heavy load on the over-all system performance. Because of this, a
CD-i player does not need much RAM or processing power, since all audio and video decoding is
performed in realtime without storing large amounts in RAM for later decoding.