Era of DEC 10 


The official name of the DEC 10 computer system is DEC. It is a member of the 4th generation of computers and was among those introduced in the middle of the 1990s. In the year 1960, DEC introduced the first PDP-10 computing system to the public. The Digital Equipment Corporation, often known as DEC, produced this computer system. PDP, which stands for “programmed data processor,” is the abbreviation for this computer system.


Being the part of 4th generation it had very advanced set of instructions. The user-mode instruction set architecture is substantially the same from the original PDP-6s through the KL-10 and KS-10. This paragraph discusses that architecture. The inclusion of multi-section extended addressing in the KL-10 is the only significant modification to the design; extended addressing, which modifies how an instruction’s effective address is generated, is briefly addressed towards the conclusion.

36-bit words and 18-bit word addresses are available on the PDP-10. Instruction addresses immediately map to physical memory in supervisor mode. Addresses are converted to physical memory in user mode. In earlier models, a user process had access to both a “high” and “low” memory: addresses with a 0 top bit utilised one base register, while higher addresses used a different base register. Each unit is continuous. With the advent of paged memory access, later architectures could support non-contiguous address spaces. The memory locations 0 through 15 can also be used to address the general-purpose registers of the CPU.

Further sets of instruction

The instruction set has a great deal of symmetry. Each instruction has a 23-bit effective address field that is made up of a 1-bit indirect bit, a 4-bit register code, and an 18-bit offset. It also has a 9-bit opcode, a 4-bit register code, and a 4-bit register code. The effective address is calculated before an instruction is executed. The effective address calculation is repeated using that word, adding the register (if not register zero) to the offset, until an indirect word with a zero indirect bit is reached. If the indirect bit is 1, a “indirect word” containing an indirect bit, register code, and offset in the same positions as in instructions is fetched at the calculated address and the process is repeated using that word, adding the register (if not register zero) to the offset.


The PDP-10 operating system’s initial moniker was just “Monitor,” but TOPS-10 eventually replaced it. At some point, the PDP-10 system was given the new moniker DECsystem-10. The WAITS operating system developed at Stanford University and the CompuServe time-sharing network were both built on early iterations of Monitor and TOPS-10.

Over time, some PDP-10 users started using operating systems built from key components created by companies other than DEC. For instance, the primary Scheduler, the Disk Service, and so on, can all originate from different universities. Commercial timesharing providers like CompuServe, On-Line Systems (OLS), and Rapidata had highly skilled internal systems development teams so they could alter the operating system as necessary for their own companies without being reliant on DEC or others.

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