And they're not strictly just a disk. It's more like a complex multiplexing system for an array of disks. It has interesting capabilities like "channel programs" that persist to this day which allow you to send miniature programs to the disk controller to have it seek out the precise record you're looking for in one of several access modes.
IBM still provides almost the entirety of it's OS documentation online:
> send miniature programs to the disk controller to have it seek out the precise record you're looking for
A very long time ago, a guy I used to work with was porting a sales and stock control database he'd written on the Commodore PET to a PC. By then he had a 286 with a 20MB hard disk and 2MB of RAM to play with - whopping stuff! - but his original program would assemble up a query routine, and transmit it to the 6502 in the PET disk drives over HPIB. Then it would chunter away discovering the records it needed to construct a reply while the host computer could continue working as normal. It was absolutely genius stuff, and it made the whole system seem really responsive even though in reality it was pretty slow.
ISAM in all important variants pretty much required DASDs, CKDs (Count Key Data) in fact as opposed to FBAs (Fixed Block Access - which act like normal drives people are familiar with)
Tapes don't provide CKD interface and thus do not work with ISAM.
Why do you think that the presentation was done in 1964?
On Youtube there is no mention about the date.
OS/360 was announced in 1964 but it was first delivered more than a year later.
I doubt that such presentations were done about a product that no customers could use and which might still be changed until the first deliverable version.
So I believe that it is unlikely that this presentation was done earlier than 1965 and it is likely that it was not done before 1966. The first OS/360 versions were delivered in November/December 1965.
If the videos are indeed so old, then probably they were not intended for customers but for the internal training of IBM employees, which would match the "CONFIDENTIAL" label.
And they're not strictly just a disk. It's more like a complex multiplexing system for an array of disks. It has interesting capabilities like "channel programs" that persist to this day which allow you to send miniature programs to the disk controller to have it seek out the precise record you're looking for in one of several access modes.
IBM still provides almost the entirety of it's OS documentation online:
https://www.ibm.com/docs/en/zos-basic-skills?topic=set-what-...