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From: Stephen Fuld <sfuld@alumni.cmu.edu.invalid>
Newsgroups: comp.arch
Subject: Re: fuzzy disks, Is Parallel Programming Hard, And, If So, What Can
 You Do About It?
Date: Mon, 26 May 2025 11:16:25 -0700
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On 5/26/2025 10:42 AM, John Levine wrote:
> According to Chris M. Thomasson <chris.m.thomasson.1@gmail.com>:
>> For some damn reason I thought of a fractal disk arm, an arm that had a
>> fractal structure, the disk rotates, but the fractal arm can read from
>> many places at once? Try not to flame me too much. ;^)
> 
> Dunno about fractal, but I have used head per track disks with a fixed arm
> with many heads, and a disk with a crooked Y-shaped arm with two heads over
> two tracks. 

Yup.  And IIRC the IBM 3380 had a linear actuator with two heads per 
arm, one covering the outer cylinders, the other the inner cylinders. 
The tradeoff was shorter seeks, thus smaller seek time but higher cost 
due to more heads.


> None of them could do more than one transfer at a time but I
> think that was a limit of the electronics of the era, not a fundamental
> issue.

Depends on what you mean by more than one transfer at a time.  If you 
mean two simultaneous independent data streams to the host, that would 
require a second host connection.  But if you mean two simultaneous 
transfers into a buffer in order to get higher host transfer rate, that 
is apparently now available.

https://www.seagate.com/innovation/multi-actuator-hard-drives/

However, I think that, except for streaming applications, the bigger 
payoff is two simultaneous seeks.



-- 
  - Stephen Fuld
(e-mail address disguised to prevent spam)