John Baker wrote:
ECKD architecture provides for a maximum track (head) number of 65535.
It also provides for a maximum track capacity of 16777215 bytes.
All things considered, the maximum configuration for a single addressable
device is 2**56 bytes - 2*32 bytes.
The number of records per track is limited to 255 (excluding Record Zero).
I just can't see a capacity limitation problem.
I can see small one: nobody uses other geometry than 3390 (please, let's
forget 3380 and older stuff, I'm talking about life datacenters, not
musea).
z/OS does not support devices with 64k heads or 16M B/trk. DASD
manufacturers also does not offer such emulation.
This is capacity limitation problem.
This problem can be solved by IBM. They can do anything they decide:
- provide new geometry
- more cylinders, despite of word/halfword considerations
- more heads, longer tracks
- use 'reserved' fields in CCW
- make revolution - FBA support
- or even something completely new (linear storage)
- or drop mainframe business
- or just let it die by not changing anything.
--
Radoslaw Skorupka
Lodz, Poland
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