Running at a data transfer rate of 510 kbytes/s, the HP C1533A tape
drive can record a full 4-Gbyte DDS-2 cartridge in just over two hours,
almost an hour less than typical DDS-2 drives. Its development required
improvements in tape material, length, and thickness, new read and write
heads, a new drum design, and new methods for linearity measurement
and adjustment.
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DDS
(1989)
DDS-DC
(1991)
'$ 9 3 /$ #1(5$ (& (-31.#4"$# ( 23.1$2 $(&'3 &(& !83$2 .% # 3 38/(" + " / "(38
DDS-2
(1993)
DDS-3
(1995)
DDS-4
(1997)
DDS Format
Enabling
Technologies
• Audio DAT
• Media
Specifications
• Format
• Error
Correction
• 90-m Tape
• DCLZ
Compression
• MP+ Media
• 120-m Tape
• Thinner
Tracks
•
•
•
•
Uncompressed
Capacity
• 1.3 GBytes
• 2.0 GBytes
• 4.0 GBytes
• 12.0 GBytes
• 24.0 GBytes
Uncompressed
Transfer Rate
• 183 kBytes/s
• 183 kBytes/s
• 360 kBytes/s
to 750 kBytes/s
• 500 kBytes/s
to 1.5 MBytes/s
• 500 kBytes/s
to 3 MBytes/s
$"$,!$1 $6+$339 "* 1# .41- +
MP ++ Media
Increased bpi
New Format
PRML
Channel
(Partial
Response
Maximum
Likelihood)
• ME Media
• 180-m Tape
• Thinner
Tracks
5.+43(.- .% 3'$ 3 /$
%.1, 3
 Hewlett-Packard Company 1994
DDS-1
3.0 m
Coating
DDS-1
2.5 m
Base
Film
DDS-2
2.0 m
9.5
6.0
4.0
Back
Coating
The HP C1533A DDSĆ2 tape drive has a nativeĆmode data
transfer rate of 510 kbytes/s, 40% faster than other designs. It reĆ
cords on highĆcapacity 4ĆGbyte DDSĆ2 cartridges or on earlier DDS
media.
achieved using the DCLZ data compression standard) and
has a data transfer rate more than 2.5 times that previously
available on DDS tape drives. The HP C1533A not only reads
and writes tapes based on the DDSĆ2 format standard, but is
also able to read and write tapes based on the original DDS
format standard to provide compatibility with the large
installed base of DDS tape drives already in existence.
The DDSĆ2 format standard calls for the data to be written
on tracks that are nominally 9.1 m wide as opposed to the
previous DDS format standard, which used a 13.6Ćm track
width. The DDSĆ2 format standard also makes use of tapes
that are 120 m long rather than the previous 90Ćm and 60Ćm
tapes. These changes, defined by the DDSĆ2 format standard,
along with a data transfer rate increase to 510 kbytes/s from
183 kbytes/s (the data transfer rate seen by the user is effecĆ
tively doubled to over 1 Mbyte/s by the use of data comĆ
pression) required numerous technical developments.
The media used for DDSĆ2 are an enhancement of the existĆ
ing DDS 60Ćm and 90Ćm media. Physically, all three cartridges
look similar; they use the same cartridge shell and are all
designed to meet the same environmental and data reliability
specifications. What differentiates them, apart from the packĆ
aging, is the length of tape in the cartridge shell and the
signal characteristics or recording properties of the media.
The tape drive differentiates between the cartridge types by
the use of recognition holes in the cartridge shell.
The longer tape length is achieved by reducing the total
thickness of the tape so that the tape pack volume is the
same for 120 m as for 60 m and 90 m. Fig. 3 shows the relaĆ
tive thicknesses of the three DDS media types and a simpliĆ
fied view of the construction of the tape. To provide optimal
headĆtoĆtape contact when switching between the different
tape thicknesses (the drive needs to read and write DDSĆ1
tapes as well as DDSĆ2 tapes) the stiffness of the tapes needs
to be matched as closely as possible. However, because the
relationship between tape thickness and stiffness is a cubed
law, use of the same base film material is not possible. A
new base film material, polyamide or PA, has been develĆ
oped. It has high stiffness, and by careful design of the
 Hewlett-Packard Company 1994
0.5
0.5
0.5
Length
60 m
90 m
120 m
Thickness
13 m
9 m
6.5 m
3.81 mm
3.81 mm
3.81 mm
Base Film
PET
PET or PEN
PA
Coating
MP
MP
MP+
Width
DDS tape types. MP = metal particle. PET = polyethylene
terathalate. PEN = polyethylene naphtalate. PA = polyamide.
heads and drum, the ability to switch from one tape type to
another can be optimized.
The 120Ćm tape, at 6.5Ćm total thickness, offers the thinnest
media currently in use in the data recording industry. This
has necessitated improvements in the accuracy of the tape
guidance system within the tape mechanism and in the tape
motion tension control servo of the mechanism to prevent
media damage.
The use of thinner tracks reduces the overall system signalĆ
toĆnoise ratio and the tape was called upon to make a conĆ
tribution to reducing the deficit. An increase of +3 dB over
the existing DDS media was needed. Existing 60Ćm and 90Ćm
media use metal particle (MP) coatings. To meet the addiĆ
tional signal requirements an enhanced MP tape has been
developed and has been designated MP+. By using a combiĆ
nation of magnetic particle size reduction, increased coercivĆ
ity, increased remanence, and reduced surface roughness of
the media, the additional signal requirements were achieved.
The higher headĆtoĆtape speed of the HP C1533A DDSĆ2
tape drive compared to previous DDS drives places addiĆ
tional constraints on the media. Without efficient lubrication
the surface of the media is damaged reducing the life of the
media. There is also the possibility of the heads becoming
clogged with debris from the media. To reduce this effect
the lubrication has been modified for DDSĆ2.
The changes needed for DDSĆ2 also called for modifications
to the heads. A DDS tape drive has four heads mounted on
a rotating drum. Two heads are used for writing and two for
reading. The tape is wrapped around the drum over an
angle that is nominally 90 degrees (see Fig. 4) so that only
one head is in contact with the tape at any given time.
During a write, the first write head (designated the A write
head) contacts the tape and data is written with an azimuth
angle of +20 degrees. The first read head (designated the A
read head) contacts the tape next to verify the previously
December 1994 HewlettĆPackard Journal
Direction of Rotation
B Write Head
Metal Layer
(Sendust)
A Read Head
Head
Gap
Ferrite
Tape Direction
90
B Read Head
Glass
A Write Head
Tape
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DDS-2 Written
Track with Maximum
Deviation of 2.5 m
Nominal Track
Center Line
Path of DDS-2
Read Head with
Maximum
Deviation of
2.5 m Opposite
to the Write
† Sendust is an alloy of 85% Fe, 6% Al, and 9% Si. It was developed at the University of Sendai,
Japan.
Data Written by the A Head
Data Written by the B Head
20
9.1 m
9.1 m
6° 22′39″
; 42!#+ &/2-!4 /. 4!0%
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 Hewlett-Packard Company 1994
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Window
Head
1 .0#4'-31*7 +#,2'-,#" 2&# 9 1.#!'$'!2'-, !**1 $-0 +6'+3+ "#4'2'-, $0-+ 120'%&2 *',# -$ ± + $-0 50'22#, 20!) &'1 1.#!'$'!2'-, '1 0#$#00#" 2- 1 *',#0'27 &#
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 Hewlett-Packard Company 1994
Window Style
Drum
Windowless
Drum
Lower Drum
(Stationary)
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68000
Microprocessor
SCSI
Bus
SCSI
Controller
Data
Compression
Processor
Format
Processor
128K-Byte
Data
Compression
Buffer
1M-Byte
Main
Buffer
(+' %#.) +" 0$! DDS
Format
Data
+.)0 ,.+!//+. %2% !/ 0$! 0 %*0+ "+.)0 /0*7
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 Hewlett-Packard Company 1994
Transfer Rate (kbytes/s)
1,200
1,000
800
600
400
200
0
0
2
4
6
8
10
Transfer Size (kbytes)
12
14
16
%<-191 (%8% 86%27*)6 6%8) 3* 8,) 8%4) (6-:) %8
(%8% '3146)77-32 6%8-3 :%6-%&0) 13() ;6-8-2+ *631 1)136= 32
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 Hewlett-Packard Company 1994
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;390( %073 0-/) 83 8,%2/ 3 9670)= *36 ,)6 )**3687 -2 8=4-2+
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