From: ronkean@juno.com
Date: Mon Sep 27 1999 - 17:36:57 MDT
On Mon, 27 Sep 1999 12:27:20 +0200 KPJ <kpj@sics.se> writes:
> Do not magneto-optical media have lower read-write times than
> magnetic media?
I don't know anything about magneto-optical media, but some magnetic
media are rather slow, and no magnetic media is as fast as DRAM.
Tapes are magnetic media, and tapes are rather slow, perhaps the slowest
of all computer-related storage technologies. Hard disks (magnetic) and
CD-ROMs (optical) are somewhat faster than tape, but much slower than
volatile RAM (DRAM). There is a big operational difference between hard
disks and CDs on the one hand and tape on the other, and that is that
tape must be mechanically reeled to the spot where a read or write
operation is required, so tape has a slow average access time for random
access, very much slower than disk type geometry.
In principle, tapes could made to have about as high a data transfer rate
as hard disks, but not much effort has been put into that because tapes
are used for low-cost seldom accessed archives rather than frequent
access. Also, tapes are not suitable for numerous rewrites, as they wear
due to contact with the heads, whereas hard disks are well suited for
numerous rewrites since they do not wear (though the mechanism wears).
Tapes are much cheaper than hard disks in terms of media cost per
gigabyte.
Ron Kean
.
.
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