🚀 go-pugleaf

Dear Dan / transatlantic cousins,

I hope I can add my little bit to the shared knowledge in this thread:

> "the 9020E, which was used as a display processor, had some additional
instructions but I forget what they were."

The 9020D and 9020E Compute Elements (CEs as they were always known) were
*identical*; a plug card told the CE whether it was in a D or an E system.
It's just that the *software* used in the 9020D CCC didn't make use of the
instructions that the 9020E DCC used. See below for the additional
instructions.

> "Was there a separate principles of operations published for it, since it
introduced a number of instructions (whether or not TS)?"

Yes - "IBM 9020D and 9020E System Principles of Operation", Form A27-2734-X
(mine is -2, dated June 1st 1971, 627 pages. I'm pretty sure this was the
final version).

> "The last Center went operational around 1973. If anyone really cares I
could probably find the actual date."

There was a 23rd 9020 centre (sorry - center!) at West Drayton in the UK.
The CCC was installed during 1973 and accepted from the FAA on 31st January
1974, though it was a while before it went operational. There were actually
two separate 9020D systems at West Drayton, a Simplex (used like a
mini-NAFEC) and a Triplex - four CEs (S/360-65s) in total. They remained
operational until April 1990 when the UK Host Computer System took over, but
the PAMs remained for much longer. It's a shame the rehost wasn't on to a
9021, a S/390 mainframe! Interestingly, the 9020 designation wasn't used in
the S/390 range.

There are references to both 20 and 22 ARTCCs in this thread. Am I right in
thinking there were 20 ARTCCs + NAFEC + OKC + UK = 23 'centers'?

> "About 1/4 the way down the left hand side is a square hole. It's where a
lighted button went. Any idea what the button was (vainly hoping I can find
the correctly labeled button somewhere)? I don't think it was "Power On", as
there is a switch on the lower right quadrant labeled that."

This was the '360 compatibility mode' button. I recall it was translucent
green and engraved "360" rather than "360 MODE" (p/n 5383203 - I have one
somewhere, perhaps I could JPEG it if you're bent on an accurate
restoration). The pushbutton was backlighted when 360 compatibility mode was
active, which could only be whilst in state 1, 0, or Test in either
Supervisor or Problem mode. When not in 360 mode the CE was in 9020 mode (we
only ever took our CEs out of 9020 mode when running the diagnostic that
checked that 360 mode worked!).

Placing the CE in 360 mode inhibited certain 9020 actions that were not
compatible with IBM System/360 architecture. These were (I could explain the
acronyms if anyone's *really* interested):

1) PSBAR stepping inhibited and LOS can't be sent to an SE.
2) Logical PSBAR cleared and Physical PSBAR set to the value in ATR slot 1.
3) PSA lockout and SE stopped result in checkstop, rather than an interrupt.
4) Bits 16-19 of PSW are part of interrupt code rather than an extension of
the system mask.
5) Only IOCE 1 channels can be used - IOCEs 2 and 3 not usable.
6) Storage protect operates differently. In 9020 mode, storage key = 0 is a
key match.
7) IOCE processor is hardware-stopped when part of a 360 mode system.
8) System IPL and PSW restart can't be used as they force state 3.
9) Certain 9020 op codes became invalid, as follows:

01 SCON - Set Configuration
02 CSS  - Convert and Sort Symbols*
03 CVWL - Convert Weather Lines*
0B DLY  - Delay
0C LI   - Load Identity
0D SATR - Set Address Translation Register
0E IATR - Insert Address Translation Register
0F RPSB - Repack Symbols*
52 LC   - Load Chain*
9A SPCI - Set PCI
A0 SPSB - Store PS Base address
A1 LPSB - Load PS Base address
D8 MVW  - Move Word
   * = Display Instruction, only _used_ in 9020E system.

Also, the 9020 Direct Control feature had extensions to that of regular 360
architecture, but these were not disabled in 360 mode. Direct Control was a
byte-wide bus between CEs that could transfer data by way of RDD (Read
Direct) and WRD (Write Direct) instructions. (I wrote a BAL program running
in the CE that used this port to interface to a PC!)

> "The rightmost switch above the Rate dial has no legend but two switch
positions labeled: "L-Reg" and "M-Reg".

The CE FEMDM, fig 6-1, shows the upper legend for this switch as "IND RLR
1", the lower legend as "INDICATE RLR 1 POSITION 6". The key itself is
labelled "L REG" (up) and "M REG" (down). The photo I have of our CEs shows
that only the lower legend has been applied, though I can't make out the
exact wording (the documentation - whilst generally excellent - doesn't
always reflect reality!). I would have imagined the FAA CEs to be the same -
obviously not.

The function of the switch is - you guessed it - to display either the L or
the M register in roller 1 position 6. The L and M regs were an addition (?)
to standard 360, and were part of the set of 'Display Registers' (L, M, XY,
K, N, Mixer). They were used (exclusively?) by the display instructions
above. There obviously wasn't enough room on the rollers to display all the
necessary information, hence this toggle.

[Set Answermode = Off]

The 9020D/E CEs (360-65s) were referred to as 7201-02s in much of the IBM
documentation, following the standard IBM nomenclature. The Input Output
Compute Elements or IOCEs (360-50s) were 7231-02s. The CEs in the 9020*A*
systems (360-50s) were 7201-01s. This is most confusing, as the 'box' number
7201 without the model number refers to both a 360-50 and a 360-65! The
basic difference is that 360-50s were 32 bit machines, and 360-65s were 64
bit machines. The regular (non-9020) 360-50 was box number 2050, and the
360-65 box number 2065.

I wouldn't be surprised if the RPSB instruction (Repack Symbols) takes the
prize for the most complex instruction ever implemented in the history of
mainframe computing - certainly of the era. Any comments? (I guess this
should be a new thread - if there isn't one on this topic already.)

Regards

Chris Bigos

FAA Academy 9020 Class of 79/80

Email: Chris...@COLDmail.com
(Make the obvious temperature change to the spam deflector)