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Announcement date: October 1977
Codename: Star
OS support (VMS): VMS V1.5
CPU Details
CPU name (VMS): KA780
Number of processors: 1
CPU technology: Bipolar Schottky
CPU cycle time: 200ns [1]
Instruction-buffer: 8 bytes [1]
Translation-buffer: 128 entries [1]
Control store: 4K 99-bit words [1]
Gate delay: 3ns
User Writable Control Store: 2K 99-bit words [1]
Cache: 8KB [1]
Compatibility mode: Yes [1]
Console processor: LSI-11 [1]
Console device: RX01 [1]
Minimum memory: 2MB
Maximum memory: 64MB
Physical address lines: 30
Memory checking: 8-bit ECC/longword [1]
Max I/O throughput: 5.0MB/s
MASSBUS: 4 @ 2.0MB/s
UNIBUS: 4 @ 1.5MB/s
LAN support: optional
VUPs: 1.0 [2]
A 'typical' VAX-11/780 marketing image

The VAX-11/780 was the first member to ship of the VAX-11 family of larger computers. The VAX series was conceived as the successor to the successful PDP-11 series of minicomputers, and in order to make the VAX seem more PDP-11 friendly, they retained the -11 moniker for the first VAXen, hence the -11/780 designation.

It was announced on October 25th, 1977 at Digital Equipment Corporation's Annual Meeting of Shareholders.[4]

One of the main design goals was to increase the address space available, in fact the VAX acronym originally stood for Virtual Address eXtension).[3]

The first VAX-11/780 systems shipped with one quarter of a megabyte of memory, built from 4Kb chips.[3]

The 11/780 didn't have normal firmware, instead it loaded its microcode from floppy. There was also the VAX-11/785, which was an upgraded version.

The VAX-11/780 was given the codename "Star" and its operating system, VAX/VMS, was codenamed "Starlet".[4] VAX/VMS Version V1.0 shipped in 1978, along with the first revenue-ship 11/780s.

Operating Systems

An actual VAX-11/780 system

The 11/780 was to ship with VMS 1.0.


SIMH is the only known emulator for the 11/780. SIMH can address up to 128MB of RAM emulating an 11/780. Also the following peripherals are emulated:

  • CPU VAX-11/780 CPU
  • TLB translation buffer
  • SBI system bus controller
  • MCTL0,MTCL1 memory controllers, MS780C with 4MB memory each, or MS780E with 8MB-64MB each
  • UBA DW780 Unibus adapter
  • MBA0,MBA1 RH780 Massbus adapters
  • TODR time-of-day clock
  • TMR interval timer
  • TTI,TTO console terminal
  • RX console RX01 floppy disk
  • DZ DZ11 8-line terminal multiplexer (up to 4)
  • CR CR11 card reader
  • LPT LP11 line printer
  • RP RP04/05/06/07, RM02/03/05/80 Massbus disks, up to eight drives
  • HK RK611/RK06(7) cartridge disk controller with eight drives
  • RL RL11/RL01(2) cartridge disk controller with four drives
  • RQ UDA50 MSCP controller with four drives
  • RQB second UDA50 MSCP controller with four drives
  • RQC third UDA50 MSCP controller with four drives
  • RQD fourth UDA50 MSCP controller with four drives
  • RY RX211 floppy disk controller with two drives
  • TS TS11 magnetic tape controller with one drive
  • TQ TUK50 TMSCP magnetic tape controller with four drives
  • TU TM03 tape formatter with eight TE16/TU45/TU77 drives
  • XU DEUNA/DELUA Ethernet controller
  • XUB second DEUNA/DELUA Ethernet controller

More information about SIMH's VAX 11/780 emulation can be found here.

Related Documents

VAX 11/780 Architecture Handbook Vol. 1 1977-78. EB-07466-20
VAX-11/780 Hardware User's Guide. EK-11780-UG-001
VAX-11/780 Installation Manual. EK-SI780-IN-002
VAX 11/780 Hardware Handbook 1979-80. EB-17835-18
VAX Maintenance Handbook VAX-11/780. EK-VAXV2-HB-002
VAX-11/780 Diagnostic System Technical Description. EK-DS780-TD-001
VAX-11/780 Diagnostic System User's Guide. EK-DS780-UG.002
MS780-E MS780-H Memory Subsystem Technical Description. EP-780EH-TD-002
KA780 Central Processor Technical Description. EK-KA780-TD.001
Translation Buffer, Cache and SBI Control Technical Description (VAX-11/780 Implementation). EK-MM780-TD-001
MS780 Memory System Technical Description. EK-MS780-TD-001
FP780 Floating-Point Accelerator. EK-FP780-TD.001
KC780 Console Interface Board Technical Description. EP-KC780-TD-001
KC780 Family Remote Diagnosis Options Technical Manual. KC780, KC782 and KC785. EK-KC780-TM-007
VAX/11/780 Microprogramming Tools User's Guide. AA-H306B-TE
VAX-11/780 Data Path Description. AA-H307B-TE
VAX-11/780 Sofwtare Installation Guide. AA-M545B-TE
CI750 CI780 Computer Interconnects Maintenance Advisory. EP-CIVAX-RM-001
VAX-11/780 Unibus Adapter Technical Description. EK-DW780-TD.001
RH780 Massbus Adapter Technical Description. EK-RH780-TD-001
Guide to VAX-11/780 System Troubleshooting. EY-2217E-SG-0001
KA780 Field Maintenance Print Set. MP00496
DW780 Field Maintenance Print Set. MP00497
KC780 Field Maintenance Print Set. MP00534
11780 Field Maintenance Print Set. MP00539
MS780-H Field Maintenance Print Set. MP01759


[1] VAX Hardware Handbook Volume 1 - 1986.
[2] Systems & Options Catalog. European Edition. Spring 1990.
[3] VAX Architecture Reference Manual. Timothy E. Leonard. 1987. EY-3459E-DP. ISBN 0-932376-86-X.
[4] Nothing Stops It! VAX Open VMS At 20.