Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!ucsd!ucsdhub!hp-sdd!hplabs!hp-sde!hpcea!hpausla!cjh From: cjh@hpausla.HP.COM (Clifford Heath) Newsgroups: comp.arch Subject: Re: memory speed & futurology Message-ID: <2220001@hpausla.HP.COM> Date: 26 Sep 88 06:57:28 GMT References: <2179@ditmela.oz> Organization: HP Australian Software Operation Lines: 29 > It would seem that the access time on hard or optical disks is > limited by rotational speed in the long run. You can add sectors > and tracks to reduce the track to track seeks, but there is that > limiting factor. Depending who you believe, it is obvious that > the WORM has a higher limit than the magnetic disk, or exactly > the opposite. (Drifting slightly...) Given the (perhaps almost) unlimited density of optical disks, the limiting factor on rotational speed is the speed of the encoder/decoder. If you want to spin a disk with 1 million bits/track at 1000 revs/second, you've got to detect that information at 1Gbit/second. That's about two orders of magnitude more than is required by current magnetic technology. The example given is probably within reach, but it still gives a rotational latency of .5 ms, which although faster than current devices it's still not that fast. To go beyond that you eventually reach a limit at which electronics isn't fast enough to detect and serialize the information any more. Note that the optical read head is capable of these speeds, although the write head may find it harder (because of the use of heating effects). Optics in general are capable of speeds far in excess of what electronics can handle, n'est ce pas? (Blue sky on... I'm looking forward to optical computers, built as optical chips mounted directly on the fixed head of a super-fast optical disk. Pocket super-computers, here we come!) Clifford Heath, Hewlett Packard Australian Software Operation. (UUCP: hplabs!hpfcla!hpausla!cjh, ACSnet: cjh@hpausla.oz)