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 <cctalk@classiccmp.org> > wrote: > > > -----Original Message----- > From: Jon Elson <el...@pico-systems.com> > Sent: Tuesday, October 01, 2024 4:55 PM > To: Tom Gardner via cctalk <cctalk@classiccmp.org> > 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 >
