Some PC HD maker offered a drive with a clear top so you could see the heads
moving. I had a friend write a VB program to do random seeks. It was fun to
watch. Still have the drive and the program. Don’t know if the program will run
in Win 11. 😊
> On Oct 2, 2024, at 13:39, Paul Koning via cctalk
> wrote:
>
>
> -Original Message-
> From: Jon Elson
> Sent: Tuesday, October 01, 2024 4:55 PM
> To: Tom Gardner via cctalk
> Subject: [cctalk] Re: Might be antique computer parts
>>
>>> On 10/1/24 18:29, Tom Gardner via cctalk wrote:
>>>
>>> I wouldn't call the 2314 low tech - it was the highest areal density at the
>>> time, a breakthru with ferrite heads and very low cost to manufacture.
>>> Note I said cost, its profit margin was enormous, in part by putting as
>>> much expensive electronics as possible in the control unit. ??
>>> Actually the 2314 did not ship with the first 360's in 1965; it was
>>> announced in April 1965 about 1 year after the 360 announcement and AFAICT
>>> from Bitsavers document dates it didn't ship until late 1966, which FWIW,
>>> at the Computer History Museum, 1966 is also the date for first shipment of
>>> the 2414 and its ferrite heads. BTW the hydraulic actuator design goes
>>> back to the 1311 - more or less the same actuator in the 1311, 2311 and
>>> 2314.
>>
>> Well, yes, and in the days of SLT logic, everything was expensive. So,
>> putting as much of the functions in the control unit rather than the drive
>> was good. But, one thing that this mindset caused was that they could not
>> have one drive seeking while another drive was transferring. The entire
>> operation, cylinder seek, rotational seek and data transfer was all one
>> atomic operation. That really killed the throughput of the whole disk
>> system. The reason was that the IBM developers came from systems like 7070
>> and 7090 where all permanent storage was on tape, and they didn't quite
>> "get" how central disks were going to be to the 360 systems. They had the
>> CKD scheme, where you could search several cylinders for a match of some
>> arbitrary field in the DATA portion of a sector, but this resulted in
>> massive slowdown of the system, as it tied up not only the drive, but the
>> controller and the channel as well! Thus the need for the database system,
>> which would make selecting the desired record much faster.
>>
>> I didn't mean that the 2314 DISK was low tech, just that the drive, itself,
>> was quite spartan.
>>
>> Jon
>
> For the earlier 1311, lack of overlap made perfect sense. After all, the
> 1620 has no interrupts, no parallelism of any kind: every I/O operation
> stalls the CPU until the operation is finished. (That and the BB instruction
> are among the reasons why Dijkstra rejected the 1620.)
>
> Speaking of high profit margins: on the 1620, there was an extra cost option
> called "direct seek". I don't know if involved a jumper cut or some actual
> circuitry (an adder, most likely). We didn't have that, and the result is
> that a seek from cylinder x to cylinder y was done by a full retract to
> cylinder 0, followed by a seek out to y. It was amusing to watch the shaking
> resulting from a simple "incrementing seek test" -- seek to cylinder i for i
> = 0 to 99. Those last few seeks would take the better part of a second.
>
>paul
>
