In article <[email protected]>,
Andy Wood wrote:
> I believe Siemens at one time sold a system derived from the RCA Spectra.
Univac bought RCA's IBM-compatible mainframe business after RCA's then-record
losses. The Univac machines were dubbed the 90/60, 90/70, and 90/80. I
don't know what relationship Siemens might have had to the business.
> I encountered the RCA Spectra in the guise of an ICL (English Electric)
> System 4. I wrote assembly code for that which from my point of view was
> identical to S/360 assembly.
The native I/O macros were different, though our shop also had IBM DOS
macros that built the native I/O control blocks and performed simulated IBM
DOS I/O, minimizing changes to working IBM DOS Assembler programs before
recompiling them. A few of the syetm service macros were also different.
The problem-mode assembler language machine instructions were nearly
identical, though the 90/70 and 90/80 machines also implemented an AI (Add
Immediate) instruction, an RS instruction similar to MVI that added a 1-byte
signed constant to a halfword.
There were a few quirks; at release, the 90/70 microcode performed an MVC a
fullword at a time plus byte moves at the finish, with stalls and restarts
for overlapped source and destination. That made it very, very slow
processing the COBOL idiom "MOVE SPACES TO output-field-1" because that
compiled into
MVI outfld1,C' '
MVC outfld1+1(L'outfld1-1),outfld1
which was of course overlapped. A field engineering change added
special-case microcode to solve that problem.
> The operating system, about which I knew very little (and now recall even
> less), must have been quite different because the machines had several
> interrupt states each with its own set of GP registers. No chance of
> running an IBM operating system on one of those.
I recall the operating system on the Univac machines as VS/9.
Our CE, who had been with RCA before Univac bought their mainfram business,
claimed that Univac bought it for the maintenance contract revenue. If so,
they pioneered the business model that Computer Associates would later
follow in software.
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