PDP-5

The PDP-5 was Digital Equipment Corporation's first 12-bit computer, introduced in 1963.
History.
An earlier 12-bit computer, named LINC has been described as the first minicomputer and also "the first modern personal computer." It had 2,048 12-bit words, and the first LINC was built in 1962.
DEC's founder, Ken Olsen, had worked with both it and a still earlier computer, the 18-bit 64,000-word TX-0, at MIT's Lincoln Laboratory.
Neither of these machines was mass-produced.
Applicability.
Although the LINC computer was intended primarily for laboratory use, the PDP-5's 12-bit system had a far wider range of use. An example of DEC's "The success of the PDP-5 ... proved that a market for minicomputers did exist"
is:
The principal designer of the PDP-5 was the young engineer Edson de Castro who went on later to found Data General.
Hardware.
By contrast with the 4-cabinet PDP-1, the PDP-5 was a single 19-inch cabinet with "150 printed circuit board modules holding over 900 transistors." 
The PDP-5 weighed about .
A maximum of 4,096 12-bit words could be addressed.
Instruction set.
Of the 12 bits in each word, exactly 3 were used for instruction op-codes.
The PDP-5's instruction set was later expanded in its successor, the PDP-8, such that bit rotations could be combined with IAC and CLA to effectively load small constants in a single instruction. The PDP-5 was one of the first computer series with more than 1,000 built.
Software.
DEC provided an editor, an assembler, a FORTRAN II Compiler and 
a debugging tool.
Marketplace.
With a base price of $27,000 and designed for those not in need of the 18-bit PDP-4, yet having "applications needing solutions too complicated to be solved efficiently by modules systems" the PDP-5, when introduced in 1963, came at a time when the minicomputer market was gaining a foothold.