FD-400 Interface -
Pertec Peripherals
came up with this 8 inch floppy interface around 1974 and it is the predecessor
to Shugart Associates 8 inch (50 pin) floppy interface. This drive utilized a
44-pin cable with a edge card type connector that supplied power as well as data
and control signals. This drive is actually still in use today primarily on
flight simulators and CNC milling machines.
SA-400 Interface - Shugart
Associates designed the SA-400 floppy disk drive in 1978 which was the first
5.25" floppy drive to gain wide acceptance. This drive utilized a 34-pin
cable that is still used in floppy drives today. The interface was later
modified for hard drives and this modified version became the ST-506 interface.
Although the pinouts of this interface have changed slightly over the years it
is still the standard for 5.25" and 3.5" floppy disk drives.
IPI
(Intelligent Peripheral Interface)
- This hard drive interface was used on
8" and 14" mainframe and minicomputer disk drives in the 1960's and
1970's.It can be found on disk drives manufactured from Control Data Corp. which
is now part of Seagate Technology.
SMD
(Storage
Module Device) -
This hard drive interface
replaced IPI and was used on 8" and 14" mainframe and minicomputer
disk drives until it was replaced by SCSI. It can be found on disk drives
manufactured from IBM,CDC and Pertec. Later an extended version called XSMD came
out as an extended version of SMD.
ST506/412 -
This interface was developed by Seagate Technology (originally Shugart) in
1980 for use with their ST-506 hard drive (5 megabytes). It was later revised in
1981 with a feature called "buffered seek" for their ST-412 (a 10
megabytes version). Due to its design limitations you would not see this
interface on drives larger than 140 megabytes. The interface consists of two
cables, a 34 pin and a 20 pin used for drive control and data transfer. This
interface was most commonly used in 80286 computers.
ESDI (Enhanced Small Device Interface) -
An ad hoc group of controller and device manufacturers (led by Maxtor
Corporation) met to develop a standard that would increase the data capacity and
speed of the existing ST506/ST412 interface. The first standard The Enhanced
Small Disk Interface was released in 1983 but then it was decided to merge this
interface with the Enhanced Tape interface into one standard in October of 1983.
Although the cabling of this interface is the same as ST506 it performs a lot
better error checking and the encoding and decoding is performed on the drive
and not the controller making for a faster transfer rate than its predecessor.
This interface was used on disk drives at the time in the range of 138mb to
676mb.
SCSI (Small Computer System Interface) -
This interface originated
as the SASI (Shugart Associates System Interface) in 1979. It was one of
several disk interfaces of that time that worked at a logical level instead of
the widely accepted device level. Working at a logical level allowed for a
stable interface while the disk devices could change rapidly. In 1980 Shugart
Associates attempted to replace the IPI (Intelligent Peripheral
Interface) through the standards committee, but were not able to due to limited
industry acceptance. NCR added features to Shugart's original interface and in
1982 the standards committee decided to start a project for SCSI which
was to be based on SASI. During the project, optical WORM commands were added,
no longer limiting SCSI to disks. In 1986 ANSI approved SCSI as a standard.
Connecting via a 50 -pin ribbon cable, up to seven
"different" devices can be connected at the same time. This includes
hard drives, tape drives, floppy drives and even printers.
IDE (Integrated Drive Electronics) -
This interface originated
in 1988 when a number of peripheral suppliers formed the Common Access Method
Committee to push an industry-wide effort of adopting a standard software
interface for SCSI peripherals. Part of their goal at that time was to specify
what is now known as the ATA (AT Attachment Interface) which would allow an
interface to be designed into the the AT -compatible motherboards of that time.
The ATA interface usually was not mentioned at the time , it was
encompassed in the IDE term. ATA refered to the interface itself and IDE to the
hard drive. Hard drives used with this type of interface are
"intelligent" devices that have most of the controller functions built
into the drive circuit board. These drives have a 40 -pin connector that plug
directly into the motherboard.
ATA (AT Attachment
Interface) -
ATA defines a universally agreed upon register set and a 40 pin connector and
its associated signals. This is the AT bus or IDE interface.
XTA (XT Attachment) -
This was an implementation of the ATA Interface that used
an
integrated 8 bit XT controller
during the late 1980's
Although rarely used one computer
manufacturer of the time that did use it was Vendex. Miniscribe make a drive
called the MS8425XT (20Mb.) at that time.
ATA-2 -
This
was an upgrade to the ATA interface standard to provide for greatly increased
EIDE (Enhanced IDE) and FAST-ATA -
This is an
enhanced version of the ATA-2 standard
as marketed by disk drive manufacturers such as Seagate/Quantum
(FAST-ATA) and Western Digital (EIDE).
DISK DRIVE
RECORDING:
DATA ENCODING SCHEMES
FM ENCODING (Frequency Modulation Encoding) -
This is an outdated encoding scheme that was used in 8 inch floppy disk drives
during the 1970's. The problem with it was that it used up half of the disk
space for timing signals used in the encoding process. Later (in the 1980's) the
technology was refined and replaced with a new standard called MFM encoding.
MFM ENCODING
(Modified Frequency Modulation Encoding) - This is an encoding scheme was
was an enhancement to FM. Basically this scheme converts the digital bits from
the computer into a pattern of magnetic changes or "flux reversals"
that are stored on the hard drive. MFM does away with the need for timing
signals thus it is more efficient than FM. It was widely used in hard drives in
the 1980's and is still in use today in floppy drives.
RLL
ENCODING (Run Length Limited) - This is an encoding scheme that reduces the
amount of data-checking information that is stored and thus requires less flux
reversals for a given amount of data. The logic circuitry is more more
complicated than MFM but allows much more data to be recorded on the disk drive.
In RLL 2,7 the "run length" of zeros is limited to 7. The codes are
chosen so that the sequences of zeros in the codes always range from 2 to 7.
This allows for a 50% increase in disk space over MFM.
ARLL
ENCODING (Advanced Run Length Limited) - This is an advanced version of RLL
that has a run length of zeros from 3 to 9 which even further increases disk
space up to (100% over MFM).
| |
Serial ATA - New Interface for High-Performance and
Mainstream Desktop PCs
Most desktop storage systems today use a
parallel bus interface referred to as Ultra ATA/100. The parallel ATA
interface has been in use on desktop systems as the mainstream internal
storage inter-connect since the 1980s (over 15 years!). Today's PCs demand
higher speeds, more robust data integrity and flexibility for innovative
smaller designs. Physically and electrically, the current parallel bus has
run into limitations that will prevent this bus from providing higher data
transfer speeds. The move to a new technology is inevitable in the eyes of
industry leaders such as Intel, Dell, Seagate(r) and APT.
These same leaders formed the Serial ATA
Working Group (serialata.org)
and are dedicated to bringing this new technology to the forefront of
today's PCs. Serial ATA is designed to overcome the limitations of parallel
ATA while providing scalability for years to come. Setting the goal to be
compatible and at cost parity with current parallel ATA drives when in
volume, the Serial ATA Working Group is promoting the adoption of Serial ATA
in all systems where ATA drives are being used today.
What is Serial
ATA?
Serial ATA is a "serial" architecture as
opposed to today's "parallel" ATA internal disc drive bus. Serial ATA wraps
many bits of data into a packet and then at a higher speed (30 times faster)
than parallel, transfers the packet of data down the wire to or from the
host. In parallel drives today, Cyclic Redundancy Checking (CRC) is
performed on the data being transmitted back and forth-but is not performed
on the commands. Serial ATA integrates CRC on both the command and data
packet level for enhanced bus reliability. Cyclic redundancy code detects
all single and double-bit errors and ensures detection of 99.998% of all
possible errors. A Serial ATA drive can transfer data at 150 Mbytes/sec on
the bus to the host system with extremely reliable accuracy and the Serial
ATA interface will continue to allow scalability for a very long time.
Serial ATA provides
expansion for reliable performance growth
| |
Generation 1 |
Generation 2 |
Generation 3 |
| Data Rate |
150 Mbytes/sec |
300 Mbytes/sec |
600 Mbytes/sec |
| Approximate
Introduction |
Fall 2002 |
Mid-2004 |
Mid-2007 |
Additional Benefits
Serial ATA, an innovative new interface, allows
continued performance growth, enhanced data reliability, and overall
improved system dynamics above and beyond what parallel can efficiently
continue to provide. Still in its early market-entry stage, Serial ATA
provides immediate benefits to desktop users.
In addition to a faster, more reliable bus, Serial
ATA improves cabling and connectors for a robust yet simpler integration.
Gone are the days of bent pins, clumsy cabling and needlessly returned hard
drives. Serial ATA cables are thinner and longer for improved system airflow
and innovative system designs such as small form factor and consumer
electronics boxes. Connectors are easier to snap into place in a
"blind-mate" fashion, without any pins. Without the wide cables, system
integrators can easily route the longer data cables (1 meter) within the
system for simplicity or innovative designs.
Seagate Technology, a
Native in Serial ATA
The true Seagate "native" Serial ATA solution
offers customers the "real McCoy" in Serial ATA technology. By implementing
Serial ATA technology not only on the physical layer of the drive but also
in the controller, Seagate drives can communicate directly from the drive to
the host-up to the full 150-Mbytes/sec speed on the bus. In addition, the
native solution incorporates command queuing, which can be a big performance
boost in operating systems that can take advantage of that type of function.
Some drive manufacturers may not immediately offer these "native" Serial ATA
features on their first-generation Serial ATA drives.
Native Serial ATA =
150-Mbytes/sec bus speed, command queuing support, superset feature ready
(for example, first party DMA)-A True Serial ATA Controller, Not Just a
Translator Bridge Chip
An alternate way to quickly integrate Serial ATA
onto a drive is to use a "bridge" solution: the drive manufacturer inserts a
data serializer/de-serializer function before the data is sent or received
by the on-board ATA controller. Data on a bridged Serial ATA solution can
only be sent or received as fast as the ATA controller works. Since the
serial functionality is not natively tied to the drive controller link and
transport layers but is a separate function that translates data for a
parallel controller, it can only transfer at the parallel controller's
speed-100 or 133 Mbytes/sec.
The industry is ready to adopt Serial ATA
technology, and Seagate will offer its customers a high performance, true
native Serial ATA solution in the fall of 2002. Leading vendors will offer
controller cards in the fall of 2002 and motherboards with Serial ATA ports
integrated in mid-2003. |
Click here for more information on the History of
the Disk Drive!
Click here for more information on how a Disk
Drive works!
For more information about hard disk
drives go to our Product Support Page on our Corporate Website at
http://www.i-t-s.com/p_support.html.
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