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IN THE LAST TWO ARTICLES, we have covered the internal performance parameters of hard disc drives, that is, more precisely, those parameters that mostly relate to a HDD as an electromechanical device. For a brief recap, HDDs use electronic and mechanical parts and the mechanical latencies are what mostly holds back the performance of any disc drive. The main reason is the inertia of any mechanical component, starting from the spindle and the platter to the read / write heads and the actuator. Whoever read through the first two articles on the subject should at least have some basic understanding of how media density and rotational speed translate into sequential transfers, likewise, the influence of rotational latency and seek latency on the random access speed should be clear.

Interface Speed as Basis for Classification

Interestingly, however, in this respect, is that neither one of the parameters we covered so far are being used for a performance-based classification of the different disc drives on the market. Rather, we are looking at PIO, Ultra DMA, UltraATA, Parallel ATA and Serial ATA in the desktop sector and a whole bunch of SCSI in the high-end sector. For reasons of simplicity, we will leave SCSI out of the loop for the time being and concentrate on UltraDMA and Ultra ATA technology first to get some feeling about the role of the interface or, more specifically, about what is called effective host transfer rate in the industry.

By the end of this, I'll try to explain how what appears a very straightforward issue at first glance can lead to very complex system interactions with all kinds of different issues fighting against each other internally within the system.

A Brief History of ATA

ATA, short for Advanced Technology Attachment is a set of specification for interfacing of peripheral components with the system logic. All current interfacing specs fall under the general umbrella of ATA / ATAPI (ATA Packet Interface). For parallel (ATA) drives, a total of seven standards exist, from the original ATA to ATA/ATAPI-7 with the latter being supported only by Maxtor.

At One Glance (just the buzzwords)

• ATA (support for HDDs only)
• ATAPI (add support for optical drives)
• ATA-2 (faster PI/O modes and PnP support)
• ATA-3 (power management and S.M.A.R.T)
• ATA/ATAPI-4 (merging of ATA and ATAPI, formalization of UDMA-33: PIO Mode4 + Burst)
• ATA/ATAPI-5 (Ultra ATA-66 with 80-wire cabling, 48-bit LBA addressing for drives up to 128 Peta-Bytes)
• ATA/ATAPI-6 (Ultra ATA-100)
• ATA/ATAPI-7 (Ultra ATA-133)

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