9 Jun
2026
9 Jun
'26
4:21 p.m.
On 6/9/26 16:24, Tom Gardner via cctalk wrote:
Lot's of mis-information which I think I correct
below
I'm pretty sure the first shipments of the 23FD was in January 1971 the with 2835
Storage Control Unit for the 2305 Fixed Head DASD and the S/370 M155; it might have been
simultaneous but the 2835 did attach to existing S/360 M85 2880 Block Multiplexer channel
and the M85 shipped in December 1969. It was followed later that year with the shipment in
the S/370 M165 and then the rest of the S/370. FWIW, the 2835 SCU was very similar to the
3380 SCU, mainly differing due to the parallel data transfer from the drive. The 23FD was
a read only device
The 360/85 was EXTREMELY close to the 370/165, in fact it
was the prototype of the 165. Looking through principles of
operation from the two models shows instruction timings are
totally identical. The model 165 had a 23FD to load
microcode and diagnostics. The 360/85 had read-only 360
microcode, but emulators and diagnostics were loadable. I
can only assume that was done via a 23FD. The major
difference between 360/85 and 370/165 hardware was that
microcode was partially read-only in the 85, with 500 words
or writeable control store, implemented in 16-bit MST4
chips. The 165 had all microcode in writable ECL static RAM
in 64-bit chips. The /85 cache (storage buffer) was
implemented in the same 16-bit chip technology, the 165 was
done with the 64-bit chips. There were some slight
differences in the 360 vs. 370 processor status word, also.
Jon