John P Baker wrote:
[...]
You are correct that DASD manufacturers do not currently provide emulation
for 64K heads. However, PC DASD manufacturers have provided emulation for
256 tracks / cylinder for years. No hardware change is required here. Just
some revised microcode.
Not exactly.
"Just revised microcode" could mean motherboard replacement. I remember
IDE -> EIDE revolution (approx. 1994). IDE controller went from card to
motherboard. Disk size increased from 512MB to 8.4GB. No BIOS updates
were available. Many program (i.e. Windows 3.1) had problems with "big
disk" support.
Similar problems were before, at level of MS DOS 4 partition size were
increased from 32MB to 2GB. Many programs had to be changed.
The difference is that in PC world it is normal thing to replace
components every 3 years, it is normal that new shining disk requires
also new motherboard, nobody uses old (5 years old) programs, or their
users do not complain.
80 pin ribbon cable for UDMA is approx. 4 years old, but it is obsolete
by now, because "everybody uses" SATA, which is ...obsolete, because
there is new version of SATA...
Or try to insert ISA card to PC...
Compare it to mainframes:
Bus&Tag connectivity was finally dropped by IBM in z/990 - after 13
years (or similar) from ESCON introduction. What does it mean ?
That means, you still can use B&T with converter.
How old is the oldest supported disk unit ? 20? 25? 30?
--
Radoslaw Skorupka
Lodz, Poland
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