2 Oct
2024
2 Oct
'24
8:15 p.m.
-----Original Message-----
From: Jon Elson <elson(a)pico-systems.com>
Sent: Tuesday, October 01, 2024 4:55 PM
To: Tom Gardner via cctalk <cctalk(a)classiccmp.org>
Subject: [cctalk] Re: Might be antique computer parts
On 10/1/24 18:29, Tom Gardner via cctalk wrote:
Well, the IBM S/360 IOS implemented a stand-alone seek which allowed seek overlap
and pretty much eliminated seek latency. Later on in System/370 they added disconnected
command chaining and RPS which then reduced seek and rotational latency. S/360 and S/370
seemed to run fast enough for many applications not using database software. At least it
appears to me that the need for database software was driven by other market forces than
the performance of S/360 and S/370 Channel hardware
Tom
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