IDE Training Course, Part 1: A Detailed Look at the Basics and Technology – THG.RU

Introduction

When buying a computer, the two most important buzzwords are gigahertz and gigabyte – unfortunately, marketing strategists will quickly relegate other equally important factors to the back burner. But as we all know, a clock will run smoothly only if all the gear wheels turn with low friction.

In this specific case, friction refers to the storage subsystem or the hard drive of every single computer. It’s not only its capacity but also its performance that determines whether the new high-end computer will actually be zippy, or whether it will feel more like a lame duck.

The reasoning behind fast hard drives has been discussed at length in numerous articles at Tom’s Hardware Guide. From the simple data transfer to streaming in video cuts or hard disk recording up to the swap file for Windows and the time it takes to boot the system – the hard drive capacity simply can never be high enough. That’s one of the reasons why more and more users connect two or more drives in what is called a RAID configuration (Redundant Array Of Independent Disk Drives). We’ll provide detailed information on this subject in later parts of this series.

In this first part, we’ll take a closer look at the IDE interface. Though the most common, it has attracted very little attention. We’ll shed light on its history and the technical details, and examine how each standard performs.

IDE: Where It All Began

The first hard drives did not have the interfaces that are common today. Instead, the drives were mounted directly onto the controller card and inserted in the ISA slot. Because of this rather impractical design, the actual controller was moved to the bottom of the hard drive without further ado, while the host adapter still had to be connected with the ISA bus.

Today this adapter is integrated directly on the motherboard, though it’s really just an interface because the actual control logic is still located on the drive. Regardless of the protocol used, the length of the IDE interface has always been 16 bits. Modern motherboards offer two IDE interface channels, each of which can address two drives.

In the mid-80’s, Imprimis used a proprietary interface standard for 5.25″ hard drives from the Wren series (these were used and sold primarily by Compaq). When 3.5″ hard drives were introduced, this standard was promptly adopted. The name of the interface and, thus, the standard was supposed to be “PC AT,” but preference was given to a term that would not interfere with any trademarks: “Advanced Technology Attachment,” in short, ATA, a name that is still used today.

However, not only did the name remain obscure for months, a generally accepted specification was not available either. That’s why hard drives from one manufacturer often did not function with models from other sources. It was particularly problematic to detect a “slave” as a second hard drive.

At the same time, a number of different manufacturers teamed up to form the CAM committee (Common Access Method), which primarily concentrated on standardizing the SCSI specification. This organization eventually agreed to adopt the very first ATA standard based on the Imprimis interface. However, it was only in 1994, after countless changes, adaptations and amendments, that the ANSI (American National Standards Institute) accepted the proposal and declared it a standard (X3.221).

In reality, the term IDE (Integrated Drive Electronics) was coined unofficially, as there is no tangible standard behind it. Rather, it is a generic term encompassing all of the existing ATA specifications. Only Western Digital used the term “IDE” for marketing purposes, pepping it up as “Enhanced IDE.”

To support drives other than hard drives (e.g., ZIP or CD-ROM drives), the ATA standard had to be expanded under the name ATAPI (ATA Packet Interface), because the ATA instruction set was never intended to support the operation of storage drives other than hard drives.

ATA Standards at a Glance

In the following paragraphs, we’ll discuss the individual evolutionary stages of ATA. The summary table at the end will provide you with the details.

ATA-1
This is the mother of all IDE standards, from 1994. This specification provides one channel with which two drives can be run (master and slave). It supports PIO modes 0, 1 and 2 (Programmed I/0), as well as DMA modes 0, 1, 2 (Direct Memory Access) and Multiword-DMA 0. Because of its age, ATA-1 is unable to handle CD-ROM drives, as these are based on ATAPI (starting with ATA-4). Nor does it support the performance-boosting block mode or logical block addressing – with the result that the maximum usable hard drive capacity is limited to 528 MB.

ATA-2
Things just weren’t moving fast enough for hard drive manufacturers, which is why Seagate (Fast-ATA) and Western Digital (Enhanced IDE) decided to take matters into their own hands. By 1996, ANSI had managed to adopt ATA-2 as an “ATA interface with extensions” that included the following improvements:

PIO modes 3 and 4 were added, as were Multiword DMA modes 1 and 2. Furthermore, ATA-2 also supported block transfers and addressing hard drives using Logical Block Addressing (LBA). Various enhancements for simple identification of the drives were integrated as well, enabling BIOS to independently detect the hard drive and all its drive parameters for the first time.

What was left were the different terms coined by the marketing departments.

ATA-3
This standard was published as X3.298-1997 in 1997, and offered relatively few improvements. These mostly involved the reliability of the fast transfer modes (Multiword DMA 2 and PIO 4) because conventional 40-wire IDE cables often presented a source of errors. For the first time, a feature for actively improving reliability was introduced: since 1998, SMART (Self-Monitoring Analysis And Reporting Technology) has been prompting hard drives to check themselves and then report errors to BIOS.

The standard itself has been officially adapted only rarely due to the lack of faster transfer modes. Instead, many manufacturers decided to use such features as SMART without actually complying with ATA-3 specifications. That’s why compatibility issues continued to arise.

ATA Standards at a Glance, Continued

ATA/ ATAPI-4
In 1998, ANSI included the ATAPI standard (NCITS 317, see below) in the latest version of the ATA standard, making it possible to connect CD-ROM drives and other storage media. Further changes included the introduction of the UltraDMA modes 0, 1 and 2, and the recommendation to use an 80-wire IDE cable, which could bring about significant improvements in reliability. Faster modes (ATA-4), however, make the use of higher-grade cables imperative.

To safeguard data integrity, the protocol was expanded to include CRC (Cyclical Redundancy Checking), and additional commands were defined – including what is known as Command Queuing and the possibilities of command overlapping. Due to its maximum data transfer rate, the UltraDMA mode 2 would soon be known as UltraDMA/33. Modes 0 and 1, on the other hand, were never implemented by the manufacturers.

ATA/ ATAPI-5
ATA-5 was introduced under the name of NCITS 340 in 2000. UltraDMA modes 3 and 4 were the most interesting. In order to be able to use the possible bandwidth of 44 or 66 MB/s, the use of an 80-wire IDE cable was required.

With ATA-5, some old ATA commands were thrown overboard; others were modified to face the new performance realities.

ATA/ ATAPI-6
The prevailing version of the ATA standard so far includes UltraDMA mode 5 and the expansion of the LBA mode from 28 bits (with a maximum of 137 GB per drive) to 48 bits. Furthermore, Acoustic Management is included as well. This makes it possible to use software to throttle the access speed of modern hard drives, noticeably reducing the operating noise. For the first time, ergonomics is an important factor. Efforts to officially integrate commands for the faster handling of audio and video streams are currently underway.

ATA7?
This standard does not yet exist, because Serial ATA is about to be introduced and is not supported by a number of leading manufacturers. However, if ATA7 is submitted later, it is sure to include UltraDMA mode 6.

Overview: Performance of PIO Modes

Overview: Performance of DMA Modes

Overview: Performance of UltraDMA Modes

* subject to change. This standard may never be adopted officially as the successor technology, Serial ATA, is ready for takeoff.

ATAPI: CD-ROM Drives Get Connected

ATA was never intended initially to communicate with drives other than hard drives. The first CD-ROM drives used SCSI, or they were connected to the system using their own interface card – not a very advanced method, considering the fact that it basically duplicated the ATA system. By the way, the progression to ATAPI also brought higher performance to tape drives, as until then those had only been connected via the slow-paced floppy controller.

Data is sent in packets, hence the name “Packet Interface.” As a matter of fact, the ATAPI protocol no longer has anything in common with ATA; instead, it is akin to the working principle of SCSI. Unlike with hard drives, the protocol used can differ greatly from model to model, whereas in the case of today’s hard drives the protocol conforms to either UltraDMA/100 or UltraDMA/133. In addition, ATAPI absolutely needs a driver to communicate with the drive, while most of the time BIOS is able to access hard drive data directly. Booting from the CD-ROM drive has not been a problem for a while now. Yet added features, such as playing audio CDs without having to load an operating system, have been mastered by only a few motherboard manufacturers (e.g., AOpen).

For the Sake of Form: Standardization Committees

The following represents a hierarchical listing of all the organizations involved in the standardization process:

• American National Standards Institute: ANSI

  ANSI handles the development and the adoption of standards of all kinds. In doing so, however, it does not have an active role, but merely takes care of the “management” side: it appoints other organizations as Standards Developing Organizations (SDOs), which are the ones doing the actual work. Once the work is done, ANSI ultimately handles the promulgation of adopted standards.

• Information Technology Industry Council: ITIC ITIC is a group comprised of several dozens of companies. It’s the branch in charge of the development of all the standards in computer technology, hence an SDO.
• National Committee for Information Technology Standards: NCITS is a commission of the ITIC, handling the support and further development of standards within the computer industry. It used to be called X3. NCITS is deeply structured so that there are various subunits for all of the relevant areas.
• T13 Technical Committee: T13 is the unit responsible for the development of ATA today.

Saturated Capacity: Int13h Extensions and LBA

Usually, the data on a hard drive are accessed with the help of three parameters: cylinder, head and sector. However, this is only possible to a certain degree, as access takes place via the graying Interrupt 19 (13h in hexadecimal notation). This Int13h, however, needs the exact positional data to be able to access the data. It has 24 bits to do so:

• 10 bits for the cylinder number (up to 1024);
• 8 bits for the number of the head (up to 256);
• 6 bits for the number of the sector (63, as numbering begins with 1 instead of with 0).

If you do the math based on 512 bytes per sector, you’ll get a total of some 16.5 million sectors, which is equivalent to 7.88 GB (8.46 GB if you base your math on 1,000 bytes per KB).

Since there isn’t a whole lot you can do with that nowadays, the Int13h had to be expanded. A simple change (for example, from 24 bits to 32 bits) would have meant that none of the old drives could have been addressed – thus a transparent expansion of the instruction set hat to be created.

With the help of the Int13h extension, addressing is increased to a full 64 bits (equaling 9.4 billion terabytes); however, not only the BIOS but also the operating system must be able to deal with this new operating mode and address the drive accordingly, as long as it registers as an Int13h extension device. Logical Block Addressing, known as LBA mode, handles the necessary conversion of the drive geometry. In the end, it is still addressed using the CHS method (cylinder, head, sector), but LBA enables easier access via numbered sectors.

Guaranteed Safe: SMART

No, this term does not denote a hip compact car, but rather a sort of intelligent early-warning system. SMART, Self-Monitoring Analysis and Reporting Technology, permanently gets values from a modern hard drive’s several sensors.

We generally differentiate between two types of operational failure: predictable and unpredictable errors. The latter simply occur every so often, and there’s nothing you can do to prevent them (for example, the sudden defect in a chip). One example of predictable failure would be damage to the spindle motor. If you monitor the temperature of the spindle motor bearing or the time it takes to spin up, you’ll be able to detect unusual behavior days, or even weeks before the failure – in a case like this, SMART would sound an alarm during boot-up. Ideally, the user still has time to save all important data to another storage medium.

The monitoring scope may vary from drive to drive. The most common, however, includes the following factors:

• Number of Remapped Sectors
  Remapping takes places if sectors on the hard drive are about to crash, in which case backup sectors are available to compensate for the loss in capacity. Disadvantage: there’s a slight drop in performance.
• Max. Headroom
  How far away are the read/ write heads from the surface? If the distance is small, then this may presage a head crash.
• ECC Error Count
  Records the number of encountered or corrected bit errors. An increasing number may indicate a lingering defect.
• Temperature
  An increase in the drive temperature may be a sign of problems with the spindle motor.
• Data Throughput
  An inexplicable reduction in the transfer rate may also be caused by a defect.

Even if your BIOS doesn’t provide SMART support, most of the time you can determine your drive’s status using software provided by the drive manufacturer or with system tools like Norton Utilities.

Our recommendation: if BIOS or another diagnosis software sounds SMART error messages, stop using the affected drive as soon as you possibly can and contact the manufacturer’s support hotline. If your drive is still under warranty, you most likely won’t have a problem exchanging it.

Hardware Check: The Proper Cables

Modern drives with UltraDMA/66 or UltraDMA/100 require the use of 80-wire IDE cables. Though they only require 40 of them directly (it’s still a 40-wire connection), the other half makes sure that the operation is smooth.

From left to right: 50-wire SCSI-2 cable, 80-wire IDE cable, 34-wire floppy cable.

The purchase of twisted cables is a prudent investment. These offer significantly less resistance to the air that is circulating in the cabinet. They also allow you to get a better look at the inside of a computer that is so equipped.

Left: twisted floppy cable, also available for IDE. Though these cables are expensive, they don’t block essential air circulation inside the cabinet.

Dreams of the future: the cable on the left is for Serial ATA. First drives and controllers will be available from dealers as early as this summer.

Connecting and Configuring: You Don’t Have to Be a Rocket Scientist

The technical specs are quite simple: there’s one master drive and one slave drive per channel. You make the settings with jumpers directly on the drives, which are usually marked clearly nowadays.

While you can use 40-wire cables any way you like, 80-wire IDE cables are different. The connectors are color-coded – blue is the connector for the adapter, the black and gray cables are for the drives. While it is not important where you actually place the master or the slave, you should preferably use the outer connector if you connect only one drive, as otherwise signal reflections may occur.

The most valuable advice for connecting IDE devices, however, is to always use common sense. For example, you might want to avoid using an old CD-ROM drive in combination with a brand-new hard drive. For some controllers, you still can’t rule out the possibility that the total performance may suffer because of very different protocols and transmission capacities.

A Look Back on Performance: From 3.2 to 120 GB

In order to give you a better picture of the fast-paced, albeit often underestimated, development in hard drive capacity, we put various representatives of different generations to the test for you, using a modern system. We included the following drives:

UltraDMA/33: Quantum Fireball ST 3.2A
This drive was our partner in a multitude of hardware tests in all categories at the end of the 90’s. Featuring 5,400 rpm and a buffer of 256 KB, it was one of the highlights a little less than five years ago.

The Quantum Fireball ST 3.2A offered the highest performance in 1997 and 1998. Modern operating systems like Windows 2000 or Windows XP, however, lose much of their speed because of these vintage models. For new computers, remember: stay away from old drives.

UltraDMA/33: IBM DTTA351010
The DTTA series from IBM was available with either 5,400 or 7,200 rpm. Sporting a buffer of 512 KB, this drive was populated rather decently, but it was one of the final models before UltraDMA/66 was introduced.

A whopping eight different versions of the Deskstar 16GP were available. The 14GXP was quite similar technologically, and it was also IBM’s first IDE family with 7,200 rpm.

UltraDMA/66: Seagate Barracuda ATA (ST320430A)
Seagate’s first IDE hard drive with 7,200 rpm went by the name of Barracuda ATA. For today’s standards, the drive featuring a 512 KB buffer gets extremely hot and makes a lot of noise – a rough diamond of days gone by, really, quite characteristic of the wild days of the UltraDMA/66.

UltraDMA/100: Western Digital WD1200
Western Digital’s high-end drives are still counted among the best to be had in the area of hard drives. The WD1200 with a capacity of 120 GB is available with a buffer of either 2 MB or an impressive 8 MB (1200BB and 1200JB, respectively). Its rotational speed of 7,200 rpm also makes for short access times.

The WD1200 is still one of the fastest IDE hard drives on the market.

Test Configuration

Benchmarks

Data Transfer Performance

Those were the days! These days you can barely do anything with maximum transfer rates of some 8.6 MB/s (Quantum UltraDMA/33). The first truly remarkable improvement in performance was brought about by the first generation of IDE hard drives featuring 7,200 rpm and UltraDMA/66.

Burst Performance

This clearly shows what each interface has to offer. While the first two UltraDMA/33 drives had access times of some 30 MB/s, the maximum (reading from the hard drive’s cache) jumped to over 50 MB/s with Seagate’s Barracuda ATA (UltraDMA/66), and today’s UltraDMA/100 hard drives feature an impressive 86 MB/s. This upper limit will soon be pushed significantly, with the introduction of Serial ATA.

Access Time Test

Modern IDE hard drives need at least 11 ms on average to access one sector or file. If the manufacturer states shorter access times, these generally refer to the pure seek times, which do not take into account rotational latency or the time it takes to initiate the read operation. Rotational latency describes the time it takes for the requested sectors to “pass by” the read heads once these have been aligned.

I/O Benchmark

It came as no surprise that a modern hard drive is able to execute more transfers per second than the older models in this test. What was astonishing, however, was the DTTA series from IBM, which should be more up-to-date and work faster than the much older Fireball ST series from Quantum.

The reason for this can be found in its market alignment. While the Fireball ST was a high-end drive, the 5,400 rpm DTTA was designed for the mass market. IBM’s portfolio included a drive with 7,200 rpm for performance-hungry applications.

Application Benchmark Winbench 99

For several years, Winbench has been an excellent indicator of the performance you can expect from a hard drive under ordinary circumstances. This clearly shows the quantum leap made in the development process.

Conclusion: A History of Success

After SCSI, which was considered to be both powerful and reliable from the beginning, IDE and ATA frequently caused compatibility problems in the early 90’s. Drive A as the master with drive B as the slave just wouldn’t work – however, you may have gotten lucky trying it the other way around. These problems have been a thing of the past since about 1997, when IDE finally grew out of its infancy stage.

With the introduction of the UltraDMA modes, this affordable interface was able to really take off, almost eliminating its performance deficit over the SCSI drives. While only three years ago a SCSI drive’s performance still excelled, you’ll be hard pressed to find an improvement in performance if you use a drive with 10,000 rpm. Moving on to the high-end scene (esp. servers), the tide turns and expensive SCSI drives show their strengths with many I/O operations per second and huge caches.

Working with IDE devices is made really simple these days; the performance to be expected is on a very high level as well, thanks to bandwidths of up to 100 MB/s (UltraDMA/100). The first products for Serial ATA, designed to increase bandwidth to 150 MB/s and to eliminate the undoubtedly cumbersome ribbon cables, will soon be rolled out.

Nevertheless, the technology and know-how concerning RAID continue to apply; this is a subject we’ll soon address in the second part of this series.