ATA-6 began development during 2000 and was officially published as a standard in early 2002. The major changes or additions in the standard include the following:

  • Ultra-DMA (UDMA) Mode 5 added, which allows 100MBps (called UDMA/100, Ultra-ATA/100, or just ATA/100) transfers.

  • Sector count per command increased from 8-bits (256 sectors or 131KB) to 16-bits (65,536 sectors or 33.5MB), allowing larger files to be transferred more efficiently.

  • LBA addressing extended from 228 to 248 (281,474,976,710,656) sectors supporting drives up to 144.12PB (petabytes = quadrillion bytes). This feature is often referred to as 48-bit LBA or greater than 137GB support by vendors; Maxtor refers to this feature as Big Drive.

  • CHS addressing made obsolete; drives must use 28-bit or 48-bit LBA addressing only.

ATA-6 includes Ultra-ATA/100 (also called Ultra-DMA or UDMA/100), which increases the Ultra-ATA burst transfer rate by reducing setup times and increasing the clock rate. As with ATA-5, the faster modes require the improved 80-conductor cable. Using the ATA/100 mode requires both a drive and motherboard interface that supports that mode.

Besides adding the 100MBps UDMA Mode 5 transfer rate, ATA-6 also extended drive capacity greatly, and just in time. ATA-5 and earlier standards supported drives of up to only 137GB in capacity, which became a limitation as larger drives were becoming available.

Commercially available 3 1/2'' drives exceeding 137GB were introduced during 2001, but they were originally available only in SCSI versions because SCSI doesn't share the same limitations as ATA. With ATA-6, the sector addressing limit has been extended from (228) sectors to (248) sectors.

What this means is that LBA addressing previously could use only 28-bit numbers, but with ATA-6, LBA addressing can use larger 48-bit numbers if necessary. With 512 bytes per sector, this raises maximum supported drive capacity to 144.12PB.

That is equal to more than 144.12 quadrillion bytes! Note that the 48-bit addressing is optional and necessary only for drives larger than 137GB. Drives 137GB or smaller can use either 28-bit or 48-bit addressing.