Re: What is a disk arm?

["James H. H. Lampert" <jamesl@xxxxxxxxxxxxxxxxx>]

On 6/13/13 3:06 PM, Dan Kimmel wrote:
> Something like 2MB took up an entire room. Big. Heavy. Expensive.
> They would only be used for something like an index with the actual
> data held on regular disks. This was at a time when most I/O was
> through punched cards and printers. The only actual use I can think
> of was in telephone switching equipment and I'm not sure about that.

I don't think I've ever been in the same room with an operational drive 
that had multiple arms per platter.

The Merlins I alluded to were the ultimate development in unsealed-pack 
drives: voice-coil head positioning, and error correction, in a drive 
that was mounted on power-driven drawer tracks in the drive rack.

I have, however, been in the same room with a fully operational computer 
that has actual core memory, a paper-tape drive, and a typebar console 
typewriter: the Computer History Museum has a fully-restored DEC PDP-1 
on display, which they power up and demonstrate twice a month. Because 
it uses core memory, it does not have to be IPL'd when it's powered up: 
core memory doesn't forget its contents with the power off (it does, 
however, forget when you read it, requiring you to refresh each bit as 
it's read).

They also have one of only two operational specimens of Babbage's 
"Difference Engine 2." It was funded by Nathan Myhrvold, and built by 
the London Science Museum, in return for his funding the completion of 
their specimen.

Alas, I don't think the CHM has any AS/400s on display. And while I know 
they have Merlin packs, and might have Merlin drives, they don't have 
any of them on display. (They do have a Winchester pack on display, though.)

--
JHHL