For those interested in the vintage 6502/65c02 MPU

Don't worry. You won't need to construct the
monstrosity shown in the photo to run S/O/S
SyMon III. The version presented here has
been modified so that it has minimum
hardware requirements:
NMOS or CMOS 6502 MPU(6502,65c02)
8k EPROM
1k RAM
ACIA(6551,65c51) three-wire serial port

This scaled-back system operating software
will fit within a 2764 or similar 8k x 8
read-only memory device, and requires
768 ($300) bytes of RAM. (more, of course,
if you want to run your own applications!)

S/O/S SyMon III has the following features:

Three-wire RS-232 serial device driver
(uses the IRQ interrupt for serial input
and has a 256 ($100) byte input buffer),
2x16 LCD module driver (use is optional),
Monitor with enhanced functions:
assembler, text editor,
Provisions for "copy & paste" method of
program storage/retrieval as well as
transfers between two SyMon systems,
Text or byte-string search functions,
Decimal-to-hex/hex-to-decimal conversion,
ASCII-to-hex/hex-to-ASCII conversion.

above: S/O/S system with (almost) everything...
It has the following:
CMOS 6502 MPU running at 1.77778 MHz:
-Rockwell(R65C02P2)
16k system program ROM:
-Hitachi(HN4827128G-25)
40k total system RAM:
-Toshiba(TC5564PL-15), NEC(D43256C-12L)
Lowest 8k RAM is non-volatile
Battery backed real-time clock:
-Dallas Semiconductor(DS1216)
RS-232 serial port:
-Rockwell(R6551AP)
Parallel (Centronics) printer port:
-Motorola(MC6821L)
Programmable priority 8 Ch. interrupt controller:
-Advanced Micro Devices(AM9519ADC)
640k double-sided floppy disk drive:
-SMC(FDC9797,FDC9229BT)
Full ASCII keyboard:
-Intel(D8279-5)
TTL monochrome 80x20 CRT video display
using 16 MHz dot clock with individuallly
controllable two-level character brightness:
-Rockwell(R6545-1AP)
8k custom video character generator ROM
with four font styles:
-Texas Instruments(TMS2764-25JL)
32k video display buffer RAM:
-NEC(D43256C-12L)
32k video display ROM (user's guide text):
-Advanced Micro Devices(AM27C256-90DC)
Console mounted video scrolling control
(allows scrolling up to 8 full screens)
Programmable sound generator:
-General Instruments(AY-3-8910)
Text-to-speech processor pair (with 2k buffer):
-General Instruments(CTS256A-AL2)
-General Instruments(SPO256A-AL2)
Buffered address/data/control busses for
external I/O hardware
Memory and I/O DMA capability