The PDP-11/05 was designed as a lower cost replacement for the 11/20. The machine could address up to a maximum of 56KB of core memory.

The CPU (KD11-B) was based around MSI and SSI logic with a microcoded instruction set. No floating point or memory management options were available for this model.

The minimum system configuration for a PDP-11/05 was:

• KD11-B CPU
• 4KB Core memory (900ns cycle time)
• Programmer's console
• Teletype control
• Power fail/auto restart
• Power supply
• 4-level interrupt system

The computer could be supplied in either a 5.25" (9 slots) or 10.5" chassis (20 slots).