VAX-11
| Company type | Product line |
|---|---|
| Industry | Computer hardware |
| Founded | 1976 |
| Founder | Digital Equipment Corporation (DEC) |
| Defunct | 1988 |
| Successor | MicroVAX series, VAX 8000 series |
| Headquarters | United States |
Area served | Worldwide |
| Products | 32-bit superminicomputers |
| Parent | Digital Equipment Corporation (DEC) |
The VAX-11 series represents a now-obsolete line of 32-bit superminicomputers that operated using the Virtual Address eXtension (VAX) instruction set architecture (ISA). These systems were designed and produced by Digital Equipment Corporation (DEC), with development commencing in 1976. A notable feature was their ability to execute user mode PDP-11 instructions (hence the "-11" suffix), offering a compatibility bridge for existing PDP-11 users.
The inaugural model, the VAX-11/780, was unveiled in October 1977. Competing companies such as Data General and Hewlett-Packard were unable to keep pace with the swift advancements introduced by the VAX architecture. In 1982, DEC expanded the lineup with more affordable variants including the 11/750, 11/730, and 11/725. More advanced models originally labeled as VAX-11/790 and 11/795 were later rebranded under the VAX 8600 series.
The production of the VAX-11 family ceased in 1988, succeeded by the MicroVAX series for entry-level applications and the VAX 8000 series targeting high-end markets. Among its models, the VAX-11/780 stands out as one of the most influential and extensively analyzed computers in computing history.
VAX-11/780
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The VAX-11/780, internally referred to as "Star," was launched on October 25, 1977 during DEC's Annual Shareholders Meeting. This system marked the debut of the VAX architecture. Its central processing unit (CPU), designated KA780, utilized Schottky transistor-transistor logic (TTL) technology operating at a cycle time of 200 nanoseconds (equivalent to a frequency of 5 MHz), and incorporated a small cache memory of 2 KB. Both memory and input/output operations interfaced through the Synchronous Backplane Interconnect (SBI).
The CPU was microprogrammed with microcode stored partly in PROM and partly in a writable control store loaded at startup from an 8-inch floppy disk via an auxiliary PDP-11/03 processor responsible for running diagnostic routines.
At launch, memory support extended up to a maximum of 8 MB through one or two MS780-C controllers—each capable of handling between 128 KB and 4 MB. Later enhancements introduced MS780-E controllers which increased total addressable memory capacity to as much as 128 MB. The KA780 CPU featured a physical address space of 29 bits allowing for a theoretical maximum memory size of up to 512 MB. Memory modules consisted of ECC-protected MOS RAM chips arranged on array cards managed by dedicated memory controllers.
For input/output connectivity, the VAX-11/780 employed Unibus for slower peripheral devices and Massbus for high-speed storage units such as disk and tape drives. Following the release of RA series drives in December 1982, Unibus also accommodated certain high-performance peripherals. Standard configurations included one Unibus slot (expandable up to four) and optional Massbus interfaces (up to four). Additionally supported was Computer Interconnect (CI), DEC’s proprietary network technology facilitating disk sharing across multiple VAX systems within a VMScluster environment.
DEC established the performance of the VAX-11/780 as a benchmark unit termed one VAX Unit of Performance (1.0 VUP). Subsequent systems were evaluated relative to this baseline—for example, a machine rated at 2.0 VUPs would deliver twice the processing speed compared to the original VAX-11/780 model.
VAX-11/782
Introduced in 1982 and known by the codename "Atlas," the VAX-11/782 is a dual-processor adaptation of the VAX-11/780. Both CPUs connect to the MA780 multiport memory bus and function in an asymmetric multiprocessing arrangement: the primary processor manages all input/output operations and process scheduling, while the secondary processor focuses on demanding computational workloads. This setup yields performance up to 1.8 times greater than a single VAX-11/780.
This system traces its origins to a "dual VAX-11/780" prototype crafted by George H. Goble and his team at Purdue University during their exploration of multi-CPU Unix kernel enhancements.
VAX-11/784
The VAX-11/784, nicknamed "VAXimus," represents a rare four-processor variant within the VAX-11/780 family. Like the 11/782, it employs asymmetric multiprocessing with four KA780 CPUs sharing access to the MA780 memory bus. Its performance is rated at 3.5 VUPs. Notably, Avie Tevanian, co-founder of the Mach kernel initiative, utilized a VAX-11/784 to run early Mach kernel versions.
VAX-11/785
Launched in April 1984 under the codename "Superstar," the VAX-11/785 features an enhanced KA785 CPU operating at a 133 ns cycle time (7.52 MHz), compared to the KA780’s 200 ns (5 MHz), achieving 1.5 VUPs performance. This speed increase was made possible through Fairchild's Advanced Schottky TTL (FAST) logic technology.
VAX-11/787
The VAX-11/787 is believed to be a dual-processor variant of the VAX-11/785; however, details regarding its production remain unclear.
VAX-11/750
The VAX-11/750, code-named "Comet," is a compact and lower-performance VAX system introduced in October 1980, utilizing bipolar gate array technology. This design reduced power usage and enhanced reliability compared to the VAX-11/780. The KA750 CPU runs at a 320 ns cycle time (3.125 MHz) with a performance rating of 0.6 VUPs. Memory capacity ranges from 2MB when paired with an L0011 controller up to 14MB using an L0022 controller.
Unlike the 11/780, which boots from an 8-inch floppy disk via its console processor, the VAX-11/750 initiates booting and diagnostics through a TU58 DECtape II cassette drive.
VAX-11/751
Designed for more demanding environments, the VAX-11/751 is a ruggedized, rack-mounted variant of the VAX-11/750.
VAX-11/730
Released in April 1982 and assigned the codename "Nebula," the VAX-11/730 is a smaller, lower-performance bit-slice implementation based on AMD Am2900 components. Its KA730 CPU operates at a 270 ns cycle time (3.70 MHz) with a performance rating of 0.3 VUPs and supports up to 5MB of memory.
VAX-11/725
Referred to as "LCN" ("Low-Cost Nebula"), this budget-friendly model shares the KA730 CPU but is housed in a more compact enclosure designed for reduced noise levels (55 dB) and lower heat output (maximum 575 W), making it suitable for office settings. It supports up to 3MB of memory.
VAX-11/790 and VAX-11/795
The designations VAX-11/790 and VAX-11/795 correspond to what later became known as the VAX 8600 and VAX 8650, respectively.
Remaining machines
- Prior to its permanent closure, the Living Computer Museum in Seattle operated a VAX-11/780-5 running OpenVMS version 7.3.
- The Computer History Museum located in Mountain View possesses three units of the VAX-11/780 along with one each of the models VAX-11/725, VAX-11/730, and VAX-11/750.
- Germany’s RECHENWERK Computer & Technikmuseum Halle exhibits both a VAX-11/730 and an uncommon East German clone known as the Robotron K 1840.
- The Verde Binario retrocomputing collective maintains a functioning VAX-11/780, honored with its own commemorative calendar.
- Pennsylvania’s Large Scale Systems Museum houses several systems including the VAX-11/785, VAX-11/780, VAX-11/750, and VAX-11/730.
- Indiana University Bloomington’s Luddy School of Informatics features a display including a VAX-11/780 alongside other computers from that era.