Parallel ATA

By James Pyles

The most recent parallel Advanced Technology Attachment (ATA) hard drive interface is the ATA/133. This refers to the data transfer rate of the hard drive interface in MB/sec. The ATA/133 is similar to it’s predecessors in that it uses the same 40 pin, 80 conductor cable and is fully backward compatible with the ATA/33, ATA/66, and ATA/100. Master/Slave operations between drives of different interface speeds also pose no problem.

The hard drive interface data transfer rate is dependant on the chipset used on the system board. In 1998, Intel introduced a chip set capable of transfer rates of over 66 MB/sec, making the ATA/66 possible and doubling the previous standard data transfer rate of 33 MB/sec. The ATA/100 was introduced in 2001 and the ATA/133 came shortly afterwards. All ATA specifications up to this point have been built around the parallel bus. Electrically, it’s difficult to design a bus that is both fast and wide. Speed is sacrificed for width. For this reason, the ATA/133 is thought to be the last in the line of parallel ATA drive interfaces. The next step in ATA interface standards is the Serial ATA (SATA) interface. SATA interfaces are only now beginning to become available in higher end PCs and the vast majority of current hardware still uses parallel ATA interfaces.

According to Maxtor, a major hard drive manufacturer, The ATA/133 clocks data at 133 MB/sec…faster than the ATA/100, and addresses big drives larger than 137 GB. They further state that at 32K application request size, under Windows NT, 2000, and XP operating systems, The ATA/133 reads and writes faster than the ATA/100.

What is important to know is that the ATA/133 and ATA/100 do not have sustained transfer rates of 133MB/sec and 100 MB/sec respectively. Maxtor states that in its tests of both interfaces, the ATA/133 has a sustained transfer rate of 114 MB/sec while the ATA/100 has a sustained rate of 89 MB/sec. Both interfaces have burst transfer rates, at least theoretically, of 133 and 100 MB/sec each. Maxtor states that the ATA/133’s burst rate is 28 percent faster than the ATA/100.

The figures for transfer rates differ somewhat, depending on the source. Techchannel reports that the ATA/100 has a burst transfer rate of only 85 MB/sec and that the Ultra ATA/133 has a sustained transfer rate of 45 MB/sec.

In order to upgrade your system to a faster ATA interface speed, you need a system board chipset that supports the interface speed, a 40 pin, 80 conductor cables, an operating system capable of DMA transfers, and a device capable of transferring data at the speed of the interface. These conditions are usually no problem in modern PCs.

According to, ATA/133 and ATA/100 chipsets are supported in Linux by numerous companies including Intel, AMD, and CMD Technologies. You are most likely using an ATA/100 or 133 interface on your current system and running Linux with no difficulty.

PC World Magazine tested numerous hard drives and produced a list of the Top 10 Hard drives in its August 2003 issue. Hard drives were assessed by cost, speed, software, documentation, and mounting kits. The number one drive listed is the Maxtor DiamondMax Plus 9 using an ATA/133 interface with a capacity of 120 GB and costing $135. It was the only ATA/133 listed. In the top ten were five ATA/100 drives, two Serial ATA drives, and two ATA/6 (firewire) drives. The ATA/100 drives ranged in price from $95 to $175.

Keep in mind that the ATA/100 is the most common hard drive interface on the market which may account for that particular interface placing the most drives on the list. The price difference between ATA/100 drives is in part due to the difference in capacities of each drive, from 80 GB to 160 GB. For more details on this comparison, visit:,aid,111118,00.asp.

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