ATAPI (Advanced Technology Attachment Packet Interface) Explained

What is ATAPI (Advanced Technology Attachment Packet Interface)?

ATAPI, or Advanced Technology Attachment Packet Interface refers to the extension of ATA. This is actually the standard IDE/ATA hardware interface for different fixed and removable drives.

Technically, ATAPI is designed to allow SATA and IDE controllers to support optical drives. Typically, ATAPI was adopted as a constituent of the AT Attachment in INCITS 317-1998.

KEY TAKEAWAYS

• Advanced Technology Attachment Packet Interface is an expansion of ATA and it helps in establishing a connection with the internal devices as well as helps in the maintenance of them.
• ATAPI is usually a standard interface created and designed by Western Digital as the IDE interface and is supported by the International Committee for Information Technology Standards, which is also referred to as X3.
• ATAPI is basically the developed version of the original ATA interface that offers major improvements in the performance with faster read and writes, rapid boot up of system with less use of power and production of heat.
• In simple terms, ATAPI is a protocol that carries specific types of Small Computer System Interface (SCSI) commands and responses via the AT Attachment interface.
• There are lots of ATAPI devices available and used today such as CD-ROMs, DVD-ROMs, CD-RW, tape drives, SuperDisk drives, magneto-optical drives, and a few super-floppy drives such as ZIP and LS-120, just to name a few.

Understanding ATAPI (Advanced Technology Attachment Packet Interface)

ATAPI is an interface standard developed by Western Digital. This interface is supported by the International Committee for Information Technology Standards or INCITS under the name of the Integrated Drive Electronics (IDE) interface.

Advanced Technology Attachment Packet Interface is the protocol that allows connecting a much wider variety of devices and peripherals to a computer than ATA, PATA, IDE and SATA would allow on their own.

To name a few, this particular interface allows connecting the following:

• Hard drives
• Tape drives
• SuperDisk drives

In addition to that, ATAPI is designed typically so that it allows the Serial Advanced Technology Attachment or SATA and IDE controllers to support different optical drives as well. These drives include the following:

• CD-ROM drives
• DVD-ROM drives
• Blu-ray players

Actually, AT Attachment technology does not support the particular functions necessary by the optical drives on its own.

For example, the media eject command or the way in which the controller can figure out whether or not any media is there in the optical drive, are not supported by it.

For this specific purpose, ATAPI needs to use Small Computer System Interface or SCSI commands set in the packets.

These particular commands help it to support the functions necessary for the removable drives.

However, using ATAPI offers a few significant advantages such as:

• Reading and writing data can be done much more quickly than on the traditional hard disks.
• It allows the system to boot up much more quickly and introduce the programs even quicker than that.
• It adds to the robustness of the system physically.
• It consumes much less power from the system during operation, and therefore, resulting in energy savings.
• It produces much less heat since it consumes much less power during operation.

Typically, ATAPI also refers to the devices running on command sets of Advanced Technology Attachments or ATA-6 or higher standards, by using the Packet Interface.

This basically signifies the specific way in which SCSI commands are issued to CD-ROM, DVD-ROM and other devices connected to the ATA bus.

Ideally, prior to the launch of ATA-4, ATAPI was considered as an atypical standard from ATA.

Therefore, the design was improved even further over time, and the improved version of the AT Attachment technology, the Serial ATA interface, was launched in 2003.

This was actually the result of the developments and additional progress made in the field of interface technology. The SATA interface is therefore considered as an evolved step from ATAPI.

Attributes

Here are some of the characteristics and features of the Advanced Technology Packet Interface summarized for your better understanding:

• The ATA Packet Interface was introduced by a group called the Small Form Factor (SFF) committee.
• The primary intention of this design was to allow connecting a wider range of devices and peripherals to the computer that needed utilities over and above those required by the traditional hard disk drives.
• This protocol relies heavily on SCSI commands and responses for the ATA interface to function.
• These SCSI commands and responses are embedded within the packets and help in conducting data transmission through the ATA cable.
• This extension of ATA allows connecting any device that can perform SCSI commands and responses.
• Since the devices use the ATA protocol and physical interface for communication, the ATAPI devices are typically referred to as ‘speaking ATA’ through the ATA cable while transmitting the packets.

ATAPI Commands

Usually, ATAPI uses a specific type of AT Attachments commands in a very small number. Out of these commands, the most significant one is the PACKET command (0xA0).

However, it also uses other commands such as the IDENTIFY PACKET DEVICE (0xA1) and a string of SCSI commands with different command bytes or OpCodes.

PACKET command (0xA0)

In this type of ATAPI command, every packet contains a command byte as well as 11 data bytes following it.

For example, the following byte string is sent to the ATAPI device as a command for reading the table of contents:

uint8_t atapi_readtoc[]= { 0x43 /* ATAPI_READTOC */, 0, 1, 0, 0, 0, 0, 0, 12, 0x40, 0, 0};

Typically, the ATA PACKET command functions in three separate phases particularly in the PIO mode, such as:

• In the first phase, the standard ATA IO port registers are set up with the specific ATAPI values, and then the ATA PACKET command is sent to the device just like any other AT Attachment command.
• In the second phase, a PIO data transfer to the device is prepared in the ordinary way. The ATAPI command string is sent to the device as a 6-word PIO transfer when it is ready (BSY clear, DRQ set).
• In the third phase, the LBA High and LBA Mid I/O port registers are read from the IRQ when it arrives. This indicates the byte count of the packet that the ATAPI device will send or should receive. The number of bytes is transferred in a loop and the subsequent IRQ is expected.

On the other hand, in the Direct Memory Access mode, only the first two phases take place. As for the third phase, it is handled by the device itself with the help of the PCI drive controller.

IDENTIFY PACKET DEVICE command (0xA1)

In this command, a regular ATA PIO mode command is used at the time of initialization. This particular command is exactly the same as the ATA IDENTIFY command, with the only difference being in the return information. It is only about the ATAPI devices.

SCSI commands

Here are some of the names of SCSI commands along with their respective command bytes:

• TEST UNIT READY – 0x00
• REQUEST SENSE – 0x03
• FORMAT UNIT – 0x04
• INQUIRY – 0x12
• START STOP UNIT (Eject device) – 0x1B
• PREVENT ALLOW MEDIUM REMOVAL – 0x1E
• READ FORMAT CAPACITIES – 0x23
• READ CAPACITY – 0x25
• READ (10) – 0x28
• WRITE (10) – 0x2A
• SEEK (10) – 0x2B
• WRITE AND VERIFY (10) – 0x2E
• VERIFY (10) – 0x2F
• SYNCHRONIZE CACHE – 0x35
• WRITE BUFFER – 0x3B
• READ BUFFER – 0x3C
• READ TOC/PMA/ATIP – 0x43
• GET CONFIGURATION – 0x46
• GET EVENT STATUS NOTIFICATION – 0x4A
• READ DISC INFORMATION – 0x51
• READ TRACK INFORMATION – 0x52
• RESERVE TRACK – 0x53
• SEND OPC INFORMATION – 0x54
• MODE SELECT (10) – 0x55
• REPAIR TRACK – 0x58
• MODE SENSE (10) – 0x5A
• CLOSE TRACK SESSION – 0x5B
• READ BUFFER CAPACITY – 0x5C
• SEND CUE SHEET – 0x5D
• REPORT LUNS – 0xA0
• BLANK – 0xA1
• SECURITY PROTOCOL IN – 0xA2
• SEND KEY – 0xA3
• REPORT KEY – 0xA4
• LOAD/UNLOAD MEDIUM – 0xA6
• SET READ AHEAD – 0xA7
• READ (12) – 0xA8
• WRITE (12) – 0xAA
• READ MEDIA SERIAL NUMBER / SERVICE ACTION IN (12) – 0xAB / 0x01
• GET PERFORMANCE – 0xAC
• READ DISC STRUCTURE – 0xAD
• SECURITY PROTOCOL OUT – 0xB5
• SET STREAMING – 0xB6
• READ CD MSF – 0xB9
• SET CD SPEED – 0xBB
• MECHANISM STATUS – 0xBD
• READ CD – 0xBE
• SEND DISC STRUCTURE – 0xBF

SATA vs ATAPI

• The ATAPI can write at 48X, while in comparison, the SATA can write at 40X.
• The ATAPI devices are relatively less costly than the SATA devices.
• When it comes to error correction, ATAPI seems to be a bit less reliable and flexible in comparison to SATA.
• In terms of cabling, it is much thinner and smaller in the case of SATA in comparison to ATAPI. This means that there will be better airflow inside the computer case, which will result in cooler and quieter systems.
• ATAPI is a relatively older technology with respect to SATA, which is not only newer but is also a superior technology.
• The number of devices supported by SATA is more than the ATAPI. There can be six or more SATA devices due to the large number of SATA controllers in the modern motherboards, but only two ATA devices.
• ATAPI is just a protocol used for AT Attachment. On the other hand, SATA is just a different type of ATA, called Serial ATA.
• Much unlike ATAPI, SATA can use ATAPI as well and can also work for HDDs and SSDs, though in a different way, and it doesn’t matter for the optical drives since they are all ATAPI for it.

What are ATAPI Devices?

The list of ATA Packet Interface devices include CD-ROMs, CD-RW, CD-Recordable, tape drives, DVD, a few specific types of super-floppy drives such as ZIP and LS-120, different changers, DVD-ROM drives, magneto-optical drives, and SuperDisk drives.

Conclusion

The Advanced Technology Attachment interface is an extension of the AT protocol, which allows connecting many more devices to the computer apart from the hard drives.

They offer support for the IDE and SATA controllers to allow linking optical drives, tape drives, and others for a better performance output.