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Hard Disk History and Details
Sources: Symantec Corp., Microsoft, Maxtor, IBM,
Tom's Hardware, KEPCIL Designs.
Here we look at the history and development of the Hard
Disk Drives. Included are some of the Microsoft Knowledge Base articles about the factors that are affecting sometimes
hard disk drives and which can be accessed from the above links.
BIT OF THE HISTORY:
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.
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ATA Standards at a Glance
The individual evolutionary stages of ATA.
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.
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/ 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.
Serial ATA
Often abbreviated SATA or S-ATA, an evolution of the Parallel ATA physical storage interface. Serial ATA
is a serial link -- a single cable with a minimum of four wires creates a point-to-point connection between devices.
Transfer rates for Serial ATA begin at 150MBps. One of the main design advantages of Serial ATA is that the thinner
serial cables facilitate more efficient airflow inside a form factor and also allow for smaller chassis designs.
In contrast, IDE cables used in parallel ATA systems are bulkier than Serial ATA cables and can only extend to
40cm long, while Serial ATA cables can extend up to one meter.
Serial ATA is the next generation ATA interface. It provides faster data transfer speeds, more bandwidth, more
potential for speed increases in future generations and better data integrity. Serial ATA hard ware is smaller
and more compact than traditional parallel ATA components. A powerful command set and hot plug features make SATA
very attractive for ATA RAID applications.
The most interesting performance feature of SATA is the maximum bandwidth possible. With a maximum external (burst)
data transfer speed of 150 MB per second (ATA maximum at 133 MB/second), Serial ATA improves hard drive performance
to keep pace with increasing data intensive environments such as audio/video, consumer electronics and entry-level
servers. The overall performance increase of SATA over ATA can currently be expected to be up to 5%, but improvements
in SATA technology will surely improve on that.
Serial ATA brings these powerful benefits for storage solutions:
- Improved command set for better data integrity.
- Performance increase to 150MB/s maximum external (burst) data transfer rate.
- Thin cables for easy routing and improved cooling inside a PC chassis or JBOD box.
- Maximum cable length increases to 1 meter for increased design and layout flexibility in a system.
- Connectors designed for blind mate and hot plug.
- Reduced pin count enables RAID scalability.
- Backward compatible with existing parallel ATA software and drivers.
Serial ATA supports all ATA and ATAPI devices.
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ATA-1
|
ATA-2
|
ATA-3
|
ATA-4
|
ATA-5
|
ATA-6
|
| Added PIO modes |
0,1,2 |
3,4 |
- |
- |
- |
- |
| Added DMA modes |
0,1,2Multiword 0 |
Multiword 1,2 |
- |
- |
- |
- |
| UltraDMA modes |
- |
- |
- |
0,1,2 |
3,4 |
5 |
| Maximum transfer rates |
11.1 MB/s |
16.6 MB/s |
16.6 MB/s |
33.3 MB/s |
66.6 MB/s |
100 MB/s |
| Cables |
40-wire |
40-wire |
40-wire |
40/80-wire |
80-wire |
80-wire |
| ANSIstandard, year |
X3.221-1994 |
X3.279-1996 |
X3.298-1997 |
NCITS 317-1998 |
NCITS 340-2000 |
NCITS 347-2001 |
| Added features |
- |
Block transfers, LBA, drive identification |
SMART,reliability features |
CRC, 80-wire cable |
- |
48 bit LBA |
| Known as |
ATA/IDE |
ATA/IDE |
ATA/IDE |
UltraDMA/33 |
UltraDMA/66, ATA/66 |
UltraDMA/100, ATA/100 |
Overview: Performance of PIO Modes
|
PIO Overview
|
Cycle time
|
Data transfer
|
Implemented
|
| PIO mode 0 |
600 ns |
3.3 MB/s |
Since ATA-1 |
| PIO mode 1 |
383 ns |
5.2 MB/s |
Since ATA-1 |
| PIO mode 2 |
240 ns |
8.3 MB/s |
Since ATA-1 |
| PIO mode 3 |
180 ns |
11.1 MB/s |
Since ATA-2 |
| PIO mode 4 |
120 ns |
16.6 MB/s |
Since ATA-2 |
Overview: Performance of DMA Modes
|
DMA Overview
|
Cycle time
|
Data transfer
|
Implemented
|
| Single Word DMA 0 |
960 ns |
2.1 MB/s |
Since ATA-1 |
| Multi Word DMA 0 |
480 ns |
4.2 MB/s |
Since ATA-1 |
| Single Word DMA 1 |
480 ns |
4.2 MB/s |
Since ATA-1 |
| Multi Word DMA 1 |
150 ns |
13.3 MB/s |
Since ATA-2 |
| Single Word DMA 2 |
240 ns |
8.3 MB/s |
Since ATA-1 |
| Multi Word DMA 2 |
120 ns |
16.6 MB/s |
Since ATA-2 |
Overview: Performance of UltraDMA Modes
|
UltraDMA overview
|
Cycle time
|
Data transfer
|
Implemented
|
| UltraDMA 0 |
240 ns |
16.6 MB/s |
Since ATA-4 |
| UltraDMA 1 |
160 ns |
25 MB/s |
Since ATA-4 |
| UltraDMA 2 |
120 ns |
33.3 MB/s |
Since ATA-4 |
| UltraDMA 3 |
90 ns |
44.4 MB/s |
Since ATA-5 |
| UltraDMA 4 |
60 ns |
66.6 MB/s |
Since ATA-5 |
| UltraDMA 5 |
40 ns |
100 MB/s |
Since ATA-6 |
| UltraDMA 6* |
30 ns |
133 MB/s |
With ATA-7* |
* subject to change. This standard may never be
adopted officially as the successor technology, Serial ATA, is ready for takeoff.
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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).
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
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
T13 is the unit responsible for the development of ATA today.
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GOOD TO KNOW:
1) Terminology
As Used in CONFIGURING a drive (in CMOS Setup) ...
CYLINDERS: Like tracks, the number of concentric cylinders upon which data is recorded, typically 300 to 3000.
SECTORS: Number of pie shaped wedges each track is divided into typically 8 to 64.
HEADS: Number of sides of magnetic material available to record on and hence number of read/write heads in the
disk drive typically 2 to 256.
As Used in COMPARING drive speeds (Usually advertised) ...
SEEK TIME: Average time to locate a cylinder on the drive typically 8 to 16 mS.
ACCESS TIME: Average time to locate a cylinder AND a specific sector on the drive and begin typically 10 to 30
mS.
DATA TRANSFER RATE: Number of K Bytes/second which disk can send to PC typically 500K/sec to 5000K/sec.
2) Drive Performance Issues
Seek time along is not enough to indicate the preformance of a drive. Seek time is affected by the technology used
to position the heads on the disk: Either a Band Stepper ot Voice Coil.
ACCESS TIME = SEEK TIME (Time to move to the cylinder) + ROTATIONAL LATENCY TIME (Time to wait for sector). This
is affected by Rotational Speed: at 3600 rpm, Rotational Latency is 8.33mS. Newer drives, rotating at 7200 rpm
have faster access times.
INTERLEAVE is only used for OLDER drives, not IDE or SCSI and hence is irrelevant for most modern applications.
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.
Hard Disk Drive size is sometimes informed bigger by the manufacturers than the operating system scan disk verification
confirms. Consider: 1000 bytes = 1 KiloByte, 1000 KB = 1 MegaByte, 1000 MB = 1 GigaByte and 1024 bytes = 1 KB,
1024 KB = 1 MB, 1024 MB = 1 GB. For example:
To quote the Microsoft Knowledge Base article referenced below:
"For most users, FAT32 will have a negligible performance impact. Some programs may see a slight performance
gain from FAT32. In other programs, particularly those heavily dependent on large sequential read or write operations,
FAT32 may result in a modest performance degradation."
FAT32 does NOT affect system performance.
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