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LINC-8
LINC-8 is the name of a minicomputer manufactured by Digital Equipment Corporation between 1966 and 1969. It combines a LINC computer with a PDP-8 in one cabinet, thus being able to run programs written for either of the two architectures.
The LINC-8 contains one PDP-8 CPU and one LINC CPU, partially emulated by the PDP-8. At any one time, the computer is in either 'LINC mode' or 'PDP-8 mode' - both processors can not run in parallel. Instructions are provided to switch between modes. In the LINC-8, all interrupts are handled by the PDP-8 CPU, and programs that rely on the interrupt architecture of the LINC can not be run.
The LINC is a 12-bit ones' complement accumulator machine, whereas the PDP-8, while also a 12-bit accumulator machine, operates in two's complement arithmetic.
Memory addressing on the two architectures is also different. On the LINC, the full address space is divided into 1024-word segments, two of which are selected for use at any one time: the instruction field and the data field. Direct access of data in the instruction field is possible using 10-bit addresses. The data field can only be indirectly addressed. The Instruction field and Data field are theoretically capable of being chosen from up to 32 areas of 1K 12-bit words each as the maximum architecture is 32K total words. As a practical matter, few LINC-8 systems ever were expanded to 8K total. Memory expansion is accomplished first by adding PDP-8 memory extension hardware and extended memory instructions and a few minor LINC processor modifications to address the memory beyond the basic 4K total. Once this is accomplished, 4K memory "wings" can be added in a daisy-chained buss arrangement, which in theory could be expanded out as many as seven times to implement the entire 32K. As a practical matter, it is always difficult to implement on the "regular" PDP-8, and, in the case of the LINC-8, it becomes necessary to slow down the CPU slightly just to add on the first additional 4K.
Thus, as a practical matter, LINC-8 memory segments are limited to segment 0-3, or perhaps 0-7 on the few 8K implementations. However, basic 4K machines cannot address beyond 0-3 while extended memory models can attempt to address segments 0-37 octal even if non-existent memory.
By convention, the segment 0 area is not available for normal fully emulated LINC operations. This is because the PDP-8 program usually known as PROGOFOP is loaded there to handle all interrupts, traps, etc. It is possible to write a program for a "partial" LINC CPU, meaning using only the hardware that actually exists. Whenever an operation is performed that it cannot handle, the PDP-8 operation resumes. However, the LINC operation could have been terminated for a variety of reasons. As such, it is always recommended that PROGOFOP be loaded when attempting to use "complete" LINC programs on this system.
Many operating systems were written for this machine; some were essentially slightly modified versions designed for the original LINC CPU it is partially based on. Bootup conventions allow an image of a custom version of PROGOFOP to first be loaded, followed by executing tape instructions to load the LINC-based operating system. In some cases, the bootup procedure is accomplished manually right on the LINC console switches; later systems self-start the system after loading PROGOFOP.
Other operating systems are actually more generic and are designed to mostly ignore the LINC side of things. These are PDP-8-only systems, although perhaps custom configured for the vagaries of the specifics of a LINC-8. In some cases, this means that they cannot be run on any other machine; in other cases, the LINC-8 merely represented a normal variation of drivers off of an otherwise non-descript PDP-8 system. An advantage of a PDP-8-based system is that PROGOFOP is superfluous here. If needed, the PDP-8 system can load PROGOFOP as well as a user program primarily LINC-oriented to get at the laboratory peripherals. The LINC convention of the entire first 1K being unavailable reserved for PROGOFOP is exchanged for the far smaller PDP-8 convention of reserving only 07600-07777 or the last 128-word page of the first 4K of the machine. This corresponds to a small reserved area at the end of LINC segment 3 in exchange for much greater overall flexibility.
Hub AI
LINC-8 AI simulator
(@LINC-8_simulator)
LINC-8
LINC-8 is the name of a minicomputer manufactured by Digital Equipment Corporation between 1966 and 1969. It combines a LINC computer with a PDP-8 in one cabinet, thus being able to run programs written for either of the two architectures.
The LINC-8 contains one PDP-8 CPU and one LINC CPU, partially emulated by the PDP-8. At any one time, the computer is in either 'LINC mode' or 'PDP-8 mode' - both processors can not run in parallel. Instructions are provided to switch between modes. In the LINC-8, all interrupts are handled by the PDP-8 CPU, and programs that rely on the interrupt architecture of the LINC can not be run.
The LINC is a 12-bit ones' complement accumulator machine, whereas the PDP-8, while also a 12-bit accumulator machine, operates in two's complement arithmetic.
Memory addressing on the two architectures is also different. On the LINC, the full address space is divided into 1024-word segments, two of which are selected for use at any one time: the instruction field and the data field. Direct access of data in the instruction field is possible using 10-bit addresses. The data field can only be indirectly addressed. The Instruction field and Data field are theoretically capable of being chosen from up to 32 areas of 1K 12-bit words each as the maximum architecture is 32K total words. As a practical matter, few LINC-8 systems ever were expanded to 8K total. Memory expansion is accomplished first by adding PDP-8 memory extension hardware and extended memory instructions and a few minor LINC processor modifications to address the memory beyond the basic 4K total. Once this is accomplished, 4K memory "wings" can be added in a daisy-chained buss arrangement, which in theory could be expanded out as many as seven times to implement the entire 32K. As a practical matter, it is always difficult to implement on the "regular" PDP-8, and, in the case of the LINC-8, it becomes necessary to slow down the CPU slightly just to add on the first additional 4K.
Thus, as a practical matter, LINC-8 memory segments are limited to segment 0-3, or perhaps 0-7 on the few 8K implementations. However, basic 4K machines cannot address beyond 0-3 while extended memory models can attempt to address segments 0-37 octal even if non-existent memory.
By convention, the segment 0 area is not available for normal fully emulated LINC operations. This is because the PDP-8 program usually known as PROGOFOP is loaded there to handle all interrupts, traps, etc. It is possible to write a program for a "partial" LINC CPU, meaning using only the hardware that actually exists. Whenever an operation is performed that it cannot handle, the PDP-8 operation resumes. However, the LINC operation could have been terminated for a variety of reasons. As such, it is always recommended that PROGOFOP be loaded when attempting to use "complete" LINC programs on this system.
Many operating systems were written for this machine; some were essentially slightly modified versions designed for the original LINC CPU it is partially based on. Bootup conventions allow an image of a custom version of PROGOFOP to first be loaded, followed by executing tape instructions to load the LINC-based operating system. In some cases, the bootup procedure is accomplished manually right on the LINC console switches; later systems self-start the system after loading PROGOFOP.
Other operating systems are actually more generic and are designed to mostly ignore the LINC side of things. These are PDP-8-only systems, although perhaps custom configured for the vagaries of the specifics of a LINC-8. In some cases, this means that they cannot be run on any other machine; in other cases, the LINC-8 merely represented a normal variation of drivers off of an otherwise non-descript PDP-8 system. An advantage of a PDP-8-based system is that PROGOFOP is superfluous here. If needed, the PDP-8 system can load PROGOFOP as well as a user program primarily LINC-oriented to get at the laboratory peripherals. The LINC convention of the entire first 1K being unavailable reserved for PROGOFOP is exchanged for the far smaller PDP-8 convention of reserving only 07600-07777 or the last 128-word page of the first 4K of the machine. This corresponds to a small reserved area at the end of LINC segment 3 in exchange for much greater overall flexibility.