🚀 go-pugleaf

In <44671@ucbvax.BERKELEY.EDU> chiueh@sprite.Berkeley.EDU (Tzi-cker Chiueh) writes:
| I have two questions on tape drives. Hope someone on the net can enlighten me.
| 
| 1) Although tapes are cheap, but tape drives are more expensive than disk drives.

It isn't, except for the very smallest disks, or the most expensive tape
drives (most 9 track's, for example).

|     Why is this the case? Also could someone tell me what is the breakdown of a
|    tape drive's cost. For example, the tape transport mechanism, the R/W head, 
|    and the A/D & DSP elctronics.
| 
| 2) The "position angle" of a tape head with respect to a tape in 4mm and 8mm 
|    tape drive is 90 and 200+ (?) degrees, but is 0 degree for linear scan tapes.
Yes, it is the difference between helical scan and linear drives.  The
helical scan moves the tape slowly, but has a rapidly rotating head
(on a drum).  It makes the tape transport simpler and more reliable (in theory)
for a given data density.

|    Also, does this mean that for 4mm and 8mm tapes, the head must touch the tape
|    during read/writes?

Yes, which is also the case for QIC.  Well, it doesn't actually touch
the *head* (in either case), but it contacts the 'shell' around the
heads.
--
Let no one tell me that silence gives consent,  |   Dave Olson
because whoever is silent dissents.             |   Silicon Graphics, Inc.
    Maria Isabel Barreno                        |   olson@sgi.com

In article <44671@ucbvax.BERKELEY.EDU> chiueh@sprite.Berkeley.EDU (Tzi-cker Chiueh) writes:
>Hi, 
>
>I have two questions on tape drives. Hope someone on the net can enlighten me.
>
>1) Although tapes are cheap, but tape drives are more expensive than disk drives.
>    Why is this the case? Also could someone tell me what is the breakdown of a
>   tape drive's cost. For example, the tape transport mechanism, the R/W head, 
>   and the A/D & DSP elctronics.

If disk drives had to track media like tape they would cost more.  If as many
tape drives were made & sold as disk drives they would cost less. 
I don't remember the exact numbers but the figures were like 1000:1 for
quanities manufactured.

>
>2) The "position angle" of a tape head with respect to a tape in 4mm and 8mm 
>   tape drive is 90 and 200+ (?) degrees, but is 0 degree for linear scan tapes.
>   Can someone explain what is the design consideration for this ? 

If you look inside a 4mm or 8mm drive you'll see the head mech is tilted.  This
causes the tracks to be written at ~6 deg. referenced to the bottem edge of the
tape.  The two write heads are placed ~20 deg. positive and negative in
reference to the track angle.  Every other track, written upper edge to lower
edge is at an opposite angle.  This is how azimuth recording is done.  The
track sync signals allow the head positioning mech. to advance or retard the
head speed to allow the head to be centered on the track.  When the head
wanders into the next or past track the deviation of the signal can be used
to calculate exactly how far off track center the head is located.  The linear
tape drives have all the heads fixed to write tracks parallel to the lower
edge of tape.

Several companies have been experimenting with azimuth recording on 1/4"
cartridges.  This will allow 150+ tracks on a 1/4" cartridge.  I doubt we'll
see any of these types of drives until the late 90's when, if I remember
correctly, the patent on azimuth recording runs out.


>   Also, does this mean that for 4mm and 8mm tapes, the head must touch the tape
>   during read/writes?
>

Actually you never want the tape to touch the head with any of them.  The
object is to have just a few molecules of air between the head and the tape.
I use to have a chart that showed objects in reference to a 1/4" cartridge
head.  A human fingerprint was several times the thickness of the distance
between the head and the tape.  Head design is an art.  The object is to
keep the tape wrapped around the head as close as possible without it
touching.

>Thanks.
>
>Tzi-cker


-- 
--------------------------------------------------------------------------
Al Amet (Unc Al)                                    Tallgrass Technologies
uncal@tallgrass.com                                 11100 West 82nd Street
Voice:(913)492-6002                                 Lenexa, KS 66214-3313

uncal@talgras.UUCP (Al Amet) writes:

>Actually you never want the tape to touch the head with any of them.  The
>object is to have just a few molecules of air between the head and the tape.
>I use to have a chart that showed objects in reference to a 1/4" cartridge
>head.  A human fingerprint was several times the thickness of the distance
>between the head and the tape.  Head design is an art.  The object is to
>keep the tape wrapped around the head as close as possible without it
>touching.

	All tape drives have their heads in contact with the media.
The chart that you have describes disk heads, which do float on a 
thin layer of air.   The only flexible media system that I am aware of 
that does use floating heads is the Bernouli drive.   In tape drives 
the head does wear because of the media contact.   Hard disk
heads do not wear while the drive is running.
-- 
>>>>>>>>>>>> Peter Reilley ..... pvr@wiis.wang.com ..... KA1LAT <<<<<<<<<<<<<
                     Well, that about says it.