SDS 9 Series

The 1965 SDS 92 is an incompatible 12-bit system built using monolithic integrated circuits.

Programmer-accessible registers are A (accumulator), B (extension), X (index), and P (program counter—14 bits), plus an overflow indicator.

The binary point is assumed to be immediately left of the high-order bit of the fraction.

The floating point formats are: For address generation, indexing, if specified, is performed before indirection.

The programmed operator facility allows the instruction code field to indicate a call to a vector of subroutine addresses.

The six bit instruction code allows up to 64 programmed operators (octal 00 through 77).

If the P bit is set, an instruction code of xx is treated as a call to location 1xx (octal).

Bit 9 of location zero is set to '1'b to indicate an indirect address, allowing the programmed operator routine to indirectly access the data specified in the address of the POP instruction.

The instruction format for the 910 and 920 systems is as follows: The SDS 910 weighed about 900 pounds (410 kg).

[5] The 930 offers a "memory extension system" that allows addressing more than 16284 words.

Two 3-bit "Extend Memory Registers", called EM2 and EM3, are provided which can be loaded with a value to be used as the high-order three bits of the effective address.

when the computer is started the value in EM2 is set to 2 and EM3 to 3, allowing programs to address the first 16384 words of memory.

For programs running in user mode, the high-order three bits of the address field of an instruction serve as an index to an array of eight registers (R0-R7).

A sixth bit (Pn) in each register indicates a read-only block of storage.

There are no P bits; the R0–R5 equivalents, called M0–M5, contain the read-only values 0–5, providing direct access to physical addresses 0–8K-1 (00000–177778).

The 940 also includes a facility to execute System Programmed operators (SYSPOPS), used to call monitor services.

MONARCH is not an executive system, since application programs have control of all the resources of the computer when running.

Instead it is a monitor, providing job-to-job transition and supporting services to applications.