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In March 1955, 4096 words of magnetic-core memory were added to the system, replacing the earlier Selectrons. This required all 12 bits of addressing, and caused programs that stored data in the "spare bits" to fail. Later in 1955 a 12k-word drum memory secondary storage system was added as well.
The initial system consisted of three Data General Nova minicomputers with 12k words of memory, several VST 1200 terminals, a Tektronix 4002 graphics terminal, and an HP 7200 plotter. In September 1973 the CPUs were updated to 32k words of memory. [6]
It requires a minimum of 12K words of memory (8K for the operating system and 4K for the user swap area) and a swapping device; The standard swapping device, called a drum, was a disk drive with a head assigned to each track so there was no delay waiting for a read/write head to be repositioned on the drive.
If that memory is arranged in a byte-addressable flat address space using 8-bit bytes, then there are 65,536 (2 16) valid addresses, from 0 to 65,535, each denoting an independent 8 bits of memory. If instead it is arranged in a word-addressable flat address space using 32-bit words, then there are 16,384 (2 14) valid addresses, from 0 to ...
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. Addresses 00000 8 –17777 8 (the first 8192 words of memory) are always unmodified. If ...
Some PIC microcontrollers use a 12-bit instruction word but handle only 8-bit data. 12 binary digits, or 3 nibbles (a 'tribble'), have 4096 (10000 octal , 1000 hexadecimal ) distinct combinations. Hence, a microprocessor with 12-bit memory addresses can directly access 4096 words (4 kW) of word-addressable memory.
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Of the 12 bits in each word, exactly 3 were used for instruction op-codes. [13] [15] The PDP-5's instruction set was later expanded in its successor, the PDP-8. The biggest change was that, in the PDP-5, the program counter was stored in memory location zero, while on PDP-8 computers, it was a register inside the CPU.