Parallel ATA (PATA)

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What is Parallel ATA (PATA)?

Parallel ATA (PATA) is based on the original IBM PC ISA bus. Basic PATA uses 5 address signals, two read/write signals, a 16-bit bidirectional data bus and an interrupt signal. These signals are used to access two blocks of 8-bit registers and one 16-bit register in the ATA or ATAPI device. These registers are used to send commands to a device, to receive status from the device and to transfer data in what is called PIO mode.

Most PATA implementations also support a data transfer mode called DMA. DMA requires two additional signals. There are two DMA protocols: the old ISA MultiWord (MW) DMA and the newer UltraDMA. Many years ago there was also a very slow Single Word DMA protocol.

Normally the PATA signals are used across a 40-wire or 80-wire PATA cable. PCMCIA PC Card ATA or Compact Flash are also popular interfaces used by ATA devices but these do not use a cable.

The rules for accessing the registers in an ATA or ATAPI devices are defined at two levels: 1) at the hardware level a device must implement the register access rules defined by ATA/ATAPI-x, and 2) a host must follow the register access rules defined by the command protocols - also defined by ATA/ATAPI-x.

What Happened to Parallel ATA?

It is nearly impossible to purchase new systems (motherboards) with a Parallel ATA (or PATA, aka IDE or EIDE) interface. And the same it true for Parallel ATA hard disk or ATAPI CD/DVD devices. The old Paralell ATA (PATA) interface has been replaced by the Serial ATA (SATA) interface. The only devices implementing the PATA interface that you can still buy at a retail store are Compact Flash (CF) devices.

The ATAPI interface was widely implement for CD and DVD drives but it is impossible to buy a new CD or DVD drive with a PATA interface. CD and DVD drives generally have Serial ATA (SATA) or USB interfaces.

PCMCIA PC Card ATA and Compact Flash

PCMCIA PC Card ATA and Compact Flash (CF) devices are generally solid state disk drives using flash memory technology. However, there were some very small disk drives, such as the IBM/HGST MicroDrive, that used the PC Card ATA or CF interface. The PC Card ATA and CF interfaces are basically a variation of PATA. PC Card ATA and CF adds several additional signals to allow access to other PCMCIA specific data in the device.

Pure PCMCIA PC Card ATA devices only operate in the PCMCIA defined interface modes. But a CF device supports both the PCMCIA PC Card ATA and TrueIDE (TrueATA) interface modes. In TrueIDE (TrueATA) mode a CF can be plugged onto a normal 40-wire or 80-wire PATA cable with another ATA or ATAPI device.

The Physical Interface

The PATA interface is defined by the ATA/ATAPI-x standards published by T13. Use the ATA/ATAPI-4 or -5 or -6 documents. Avoid using the ATA/ATAPI-7 or -8 documents unless you need information about a specific ATA/ATAPI-7 or -8 feature. A PATA interface must conform to the signal usage and signal timing found in these T13 documents.

Use the PCMCIA and/or Compact Flash (CFA) documents for the signal usage and signal timing of the PCMCIA PC Card ATA and/or Compact Flash (CF) interface.

Page updated 21 Feb 2015.