PDT-11

Introduction

The PDT-11 is DEC's only "official" programmable terminal offering. First announced on May 1978 with the first delivery on June 1978; over 2600 were sold. The PDT-11 (Programmed Data Terminal) is based on the DEC LSI-11 microprocessor, and supports a VT-100 display terminal or DECwriter teleprinter as the console plus up to three additional slave CRT or printer workstations. All models are available with up to 60K bytes of RAM high speed memory. The PDT-11/130 also provides up to 512K bytes of mass storage via twin tape cartridges. The PDT-11 150 provides up to 512K bytes of mass storage via two floppy disks. A single PDT-11/110 with 32K bytes of memory sold for $4,800 (1978). A PDT-11/151 with 60K bytes of RAM and twin diskette drive sold for $9,300 (1978).

The PDT-11 Series of user-programmable terminals represents another link in the Digital Equipment chain of products that provided users of distributed systems with virtually every piece of hardware that they require. As a mature product line, the PDT-11 Series continues to be available, but maintained a relatively low profile when compared to newer DEC offerings. In particular, the lower-end models' (the 110 and 130) are generally sold only on a quantity basis to OEMs and large end users, although single quantity units may be available on a refurbished basis. The processor employed by PDT-11 family members is the LSI-11, a Digital Equipment-manufactured microprocessor that was compatible with the company's popular PDP-11 minicomputer.

The man/machine interface for the terminal family can be either a DEC VT100 CRT display terminal or a DECwriter keyboard/printer terminal, depending on the PDT-11 model. Two versions of the PDT-11 family (the 11/110 and 11/130) have the processor housed within the cabinet of the VT-100. The PDP 11 Jl30 provides up to 512K bytes of mass storage via twin minicassette tape drives built into the display monitor cabinet. The PDT 11/150 has the processor housed in a separate cabinet which also housed two diskette drives. The diskettes were single sided, IBM 3740 compatible, 8-inch diameter removable platters, each of which contained 77 tracks and stores 256K bytes for a total of 512K bytes of diskette storage.

Processor

The processor in all PDT-11 terminals was the DEC LSI-11, a microprocessor version of the DEC PDP-11 and compatible with that system with minor exceptions. (For example, the PDP-11 Extended Instruction Set (EIS) is not supported, and the PDT-ll goes about handling I/O using a separate I/O microprocessor, rather than emulating the PDP-11's I/O page function.) The PDT-11's processor has a single-instruction cycle time of 490 nanoseconds, a memory access time of 400 nanoseconds, and an I/O latency of 30 to 125 microseconds, depending on the operation involved. It had a repertoire of 66 instructions.

The PDT series were desktop systems marketed as "smart terminals". The /110 and /130 were housed in a VT100 terminal enclosure. The /150 was housed in a table-top unit which included two 8-inch floppy drives, three asynchronous serial ports, one printer port, one modem port and one synchronous serial port and required an external terminal. All three employed the same chipset as used on the LSI-11/03 and LSI-11/2 in four microm chips. There is an option which combines two of the microms into one dual carrier, freeing one socket for an EIS/FIS chip. The /150 in combination with a VT105 terminal was also sold as MiniMINC, a budget version of the MINC-11.

Diskette Drive

(PDT-11/150 only): The dual diskette drives were housed with the LSI-11 processor in a separate cabinet from other system components. Each drive accommodated eight-inch diameter diskettes recorded with 77 tracks in IBM 3740 format, single side. Average access time for each diskette is 488 milliseconds. The dimensions of the diskette unit are 20.08 inches deep, 13.0 inches wide and 13.42 inches high. The front panel of the diskette unit had indicator lights which show various operating conditions. One shows when a system error occurs in self-test mode, another shows that the LSI-11 microprocessor is executing instructions, another shows the presence of power, and another shows that the system is waiting for a response from the console terminal. Two of the indicator lights are available to the user program.

DECtape Mini Cartridges

(PDT-11/I30 only): This was a mass memory magnetic tape subsystem consisting of two cartridge transports, capable of reading and writing a total of 512K bytes of data on pre-formatted, block-addressable cartridges at 800 bits per inch. The system stores information at fixed positions on the tape rather than at unknown or variable positions as in conventional magnetic tape recording. Thus, the tape is used much like a disk. Data blocks can be read or written over in random fashion without disturbing previously recorded information. The average search time for any record is 10 seconds.

Keyboard / Printer

A DECwriter teleprinter terminal may be used as a slave PDT-11 printer, a PDT-11/150 console, or an additional PDT-11 workstation attached via the optional cluster controller. The DECwriter III (LA120) prints at 180 cps. The DECwriter IV (LA38) prints at 10 or 30 cps.

Software

The PDT-11/130 and /150 utilized the RT2/PDT operating system, which is a run-time subset of RT-ll, an operating system developed for the PDT-ll Series of computers. RT11/PDT features included monitors, handlers, and utilities that supervise the PDT-11's operation and support execution of RT-11 applications. RT2/PDT can support both single-job and foreground/background modes of operation. The single job version requires 16K bytes of memory; the two-partition version, 32K bytes of memory. The PDT-11/130 and /150 support MACRO-H, FORTRAN- IV ,APL-11, BASIC-11, and MU BASIC-11 (PDT-11/150 only) programming languages, as well as the FMS-11 forms development language, which can be used to develop video form applications packages for data entry and display. Programs are developed on any full RT-11 system, then down-line loaded into mass storage for later execution. Either of two IBM 2780/3780 emulation software packages, PDT-11 2780/3780 PE and RT-11/2780, allowed the PDT-11/130 and /150 to communicate with an IBM host as an RJE terminal.

The PDT-11/130 can support either DECnet-11S or DECnet-RT for DEC network communications. The PDT-11/150 supports only DECnet-RT. The PDT-11/110, which contains no local mass storage, utilizes the RSX-11S operating system, a run-time version of RSX-11M. DECnet-S is also supported.

PDT-11/11O

This was a VT100 Terminal to which has been added an LSI-11 microprocessor, up to 60K bytes of random access memory, ports for synchronous or asynchronous communications with a host system, a port for a local printer and interfaces for up to three additional VT100 terminals or hard copy terminals. User programs may be automatically loaded from a DEC host processor or from a user selected host via user provided software.

PDT-11/13O

This is a VT100 Terminal with all of the features of the PDT-ll/llO. In addition, the 130 was equipped with dual integrated mini cartridge magnetic tape drives which provided up to 512K bytes of mass storage.

PDT-11/15O

This was a VT100 Terminal and a separate desktop cabinet which housed the LSI-11 processor, and two diskette drives on which was stored up to 512K bytes of RAM storage. The 150 also had up to 60K bytes of semiconductor memory and three ports on the terminal. One of the ports connected the terminal to a communications line. One was used to connect a local serial printer. The third was used to connect a video or hard copy terminal. An optional cluster controller permitted attaching three additional VT100s or other EIA compatible video or teleprinter terminals.

Transmission Specifications

The PDT-11 terminal family operates on full-duplex synchronous or asynchronous communication lines at switch selectable speeds ranging from 50 to 9600 bps. Parity is also switch selectable. An EIA RS 232C interface is standard on all models.