IDE Technology

IDE Basics

IDE/ATA

Integrated Drive Electronics (IDE) and AT Attachment (ATA) are the same: a disk drive configuration that integrates the controller onto the drive instead of on a card. With this configuration, interface costs are reduced, and firmware implementations are simplified.

EIDE

Contrary to popular belief, Enhanced IDE is not a standard. It is a marketing program consisting of a software part -- an Enhanced BIOS specification which breaks the 504 Mb barrier - and a hardware part that has been derived from the ATA2 (Hard Drives) and ATA p1 (Tapes, CD-Roms) standards. EIDE consists of four basic features.

• High Capacity Addressing of ATA Hard Drives - This feature is based on the AT Attachment (ATA) industry standard specification that defines how drives greater than 528 Mb are addressed by the system BIOS. Proper implementation requires that the drive, BIOS and operating system all support the ATA specification.
• Fast Data Transfer Rates for ATA Hard Drives - This feature is based on the ATA industry standard specifications for Programmed Input/Ooutput (PIO) mode 3 and Multiword Direct Memory Access (DMA) mode 1. These transfer modes support burst transfer rates of upto 11.1 MB/Sec and 13.3 MB/SEC. respectavely. The fast transfer capabilites take advantage of higher bandwidth of ATA local bus attachments, and are wasted if the drive is attached to a low bandwidth connection such as the ISA bus.
• Dual ATA Host Adapters - This feature uses a secondary host adapter address along with a secondary system interrupt (IRQ15) to address a second ATA host adapter, thus supporting upto four devices.
• Non-Hard Disk ATA peripherals - This feature is targeted at CDROM drives, tape drives and other peripherals that use the ATAPI (AT Attachment Packet Interface) specification command set. Previously, only hard drives could be connected to an IDE controller.

ATAPI

• The Western Digital authored AT attachment Packet Interface (ATAPI) specification is an EIDE and ATA specification that enables connectivity of non disk peripherals to an IDE controller. In other word, ATAPI is designed to allow devices such as CD-ROMs and tape drives to plug into an ordinary ATA (IDE) port. ATAPI is packet based interface whose command set is actually derived from SCSI. The principal advantage of ATAPI hardware is that it is inexpensive and works with existing host computer hardware and cabling.

IDE operation Modes and Speeds

PIO

Programmed I/O uses an interrupt driven method to transfer data. The following chain of events occurs:

1. A data request is made by the CPU.
2. The device (Disk Drive) retrieves the data.
3. The device then generates an interrupt to the processor.
4. The CPU responds to the interrupt and the data transfer begins.

This method is slow , but is simple and efficient in terms of hardware cost.
PIO modes are rated according to maximum data transfer speed. The modes range from 0 to 4, with a subsequent speed increase on each level. The modes and speeds are

• Mode 0 = 3.3 MB/s
• Mode 1 = 5.2 MB/s
• Mode 2 = 8.3 MB/s
• Mode 3 = 11.1 MB/s
• Mode 4 = 16.6 MB/s