Re: SUMMARY: 8mm vs. 4mm

From: Bill Wyatt (wyatt@cfa0)
Date: Thu Mar 10 1994 - 19:43:55 CST

Michael Grabenstein ( wrote:
: >In article <> (Paul Eggert) writes:
: >> (Gary Braida) writes:
: >>
: >>>Media Costs
: >>> 8mm $16 (112m data grade)
: >>> 4mm $27 (120m data grade)

Hmm. I was quoted ~$14 for 120m data grade 4mm tapes.

: > One thing here too is, that the 120M tape for 4mm is the longest
: >you can buy. The tape drives should accept 60M and 90M tapes too which are
: >cheaper. 90M tape stores 2 gig, 60M stores 1.3 gig, 120M I think is 2.7
: >gig, right? This is all without compression.

Well, 120m tape is not supported by DDS. DDS-2, however, does support it.
DDS-2 format is a little denser, so you get 4 GB per 120m tape without

: >>>Which one is faster

: >>That's true, but 8mm have about twice the transmission rate of 4mm at
: >>the same level of technology, which is not surprising given that
: >>they're twice as wide. For dumps, transmission rate is more important
: >>than seek time.
: >>
: > This is interesting, because my dumps to my 4mm tape drive have
: >always "felt" faster. But I have never really tested it (of course my 8mm
: >and 4mm are on different machines...).

It's possible that the 4mm is actually faster. If you've got a case where
the computer (or network) can't fill the 8mm buffer fast enough to keep the
tape streaming, then it has to stop and restart. This would slow it waaaay

: > I am not up on the compression 4mm tape drives, but I know there is
: >an HP tape drive that can store up to 8gig, not sure on what tape. I assume
: >120M tapes.

The DDS-2 drive (4 GB native), assuming 120m tape and compression is
quoted at up to 16 GB. In real life, expect 6 GB worst case, and average
at about 8 or so. 16 is pretty unlikely.

Bill Wyatt, Smithsonian Astrophysical Observatory  (Cambridge, MA, USA)
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