supported by peripheral options using various data formats. The 11/20 lacks any kind of memory protection hardware unless retrofitted with a KS-11 memory mapping add-on. There was also a very stripped-down 11/20 at first called the 11/10, but this number was later re-used for a different model (see below). PDP-11/45 (1972), PDP-11/50 (1975), and PDP-11/55 (1976) – A much faster microprogrammed processor that can use up to 256 KB of semiconductor memory instead of or in addition to core memory and support memory mapping and protection. It was the first model to support an optional FP11 floating-point coprocessor, which established the format used in later models. PDP-11/35 and PDP-11/40 – 1973. Microprogrammed successors to the PDP-11/20; the design team was led by Jim O'Loughlin. PDP-11/05 and PDP-11/10 – 1972. A cost-reduced successor to the PDP-11/20. DEC Datasystem 350 models from 1975 include the PDP-11/10. PDP-11/70 – 1975. The 11/45 architecture expanded to allow 4 MB of physical memory segregated onto a private memory bus, 2 KB of cache memory, and much faster I/O devices connected via the Massbus. PDP-11/34 (1976) and PDP-11/04 (1975) – Cost-reduced follow-on products to the 11/35 and 11/05; the PDP-11/34 concept was created by Bob Armstrong. The 11/34 supports up to 256 kB of Unibus memory. The PDP-11/34a (1978) supports a fast floating-point option, and the 11/34c (same year) supported a cache memory option. PDP-11/60 – 1977. A PDP-11 with user-writable microcontrol store; this was designed by another team led by Jim O'Loughlin. PDP-11/44 – 1979. A replacement for the 11/45 and 11/70, introduced in 1980, that supports optional (though apparently always included) cache memory, optional FP-11 floating-point processor (one circuit board, using sixteen AMD Am2901 bit slice processors), and optional commercial instruction set (CIS, two boards). It includes a sophisticated serial console interface and support for 4 MB of physical memory. The design team was managed by John Sofio. This was the last PDP-11 processor to be constructed using discrete logic gates; later models were all microprocessor-based. It was also the last PDP-11 system architecture created by Digital Equipment Corporation, later models were VLSI chip realizations of the existing system architectures. PDP-11/24 – 1979. First VLSI PDP-11 for Unibus, using the "Fonz-11" (F11) chip set with a Unibus adapter. PDP-11/84 – 1985-1986. Using the VLSI "Jaws-11" (J11) chip set with a Unibus adapter. PDP-11/94 – 1990. J11-based, faster than 11/84. Q-bus models The following models