VAX 11/78X
Introduction
VAX-11/780
The VAX-11/780, code-named Star, was introduced on 25 October 1977 at DEC's Annual Meeting of
Shareholders. It was the first computer to implement the VAX architecture. The KA780 central
processing unit (CPU) was built from Schottky transistor-transistor logic (TTL) devices and has a
200ns cycle time (5 MHz) and a 2 KByte cache. Memory and I/O are accessed via the Synchronous Backplane Interconnect (SBI).
The first VAX-11/780 systems shipped with one quarter of a megabyte of memory built from 4KBit dynamic RAM chips.
The 11/780 didn't have ROM based firmware, instead it loaded its microcode from an 8" floppy into writable control store (WCS).
This gave DEC the advantage
of releasing new firmware versions that further optimized the instruction set. As well, static RAM based writable control store
was faster than ROM based firmware memory for microcode execution. An LSI-11/03 with an 8" floppy was part of every VAX-11/780 and was
used to boot the microcode into the VAX WCS. The first release of the 11/780 shipped with sub-optimal microcode, but performance was
improved later with an updated microcode release. The releases shipped on 8" floppy that were loaded by the 11/03 into WCS.
Later models of the VAX architecture no longer featured the WCS option. It made sense for the first VAX models so DEC could best
optimize the instruction set and allowed DEC to add or tweak the instruction set on these early VAXen.
The VAX-11/780 originally supported up to 8MB of memory through one or two MS780-C memory controllers, with each controller supporting between 128kB-4MB of memory. The later MS780-E memory controller supported 4MBytes to 64MBytes of memory, allowing the VAX-11/780 to support up to a total of 128MBytes of memory. The KA780 has a 29-bit physical address space, allowing it to address a theoretical maximum of 512MB of memory. The memory is constructed from 4KBit or 16KBit metal oxide semiconductor (MOS) RAM chips mounted on memory array cards. Each memory controller controls up to 16 array cards. The memory is protected by error correcting code (ECC).
The VAX-11/780 uses the Unibus and Massbus for I/O. Unibus was used for attaching lower-speed peripherals such as terminals and printers. Massbus was used for higher-speed disk and tape drives. Both buses were provided by adapters that interface the bus to the SBI. All systems come with one Unibus as standard, with up to four supported. Massbus was optional, with up to four supported. The VAX-11/780 also supported Computer Interconnect (CI), a proprietary network to attach disk drives and potentially share them with other VAX computers. Later, this feature was used to connect VAX computers in a VMScluster.
Digital used the performance of the VAX-11/780 as a reference point for describing the performance of subsequent VAX models. The performance of the VAX-11/780 became known as 1 VAX Unit of Performance (or 1.0 VUPS). Other VAX models were rated as a multiple of the VAX-11/780's performance, for example, a 2.0 VUPS VAX would be twice as fast as the VAX-11/780.
| VAX-11/780 SPECIFICATIONS |
|---|
CPU
|
VAX-11/780 Modules:
- M8237 TERMINATOR SILO
- M8218 SBL LOW BIT INTERFACE
- M8219 SBH HIGH BITS INTERFACE
- M8220 CAM CPU CACHE ADAPTER MATRIX
- M8221 CDM CPU CACHE DATA MATRIX
- M8222 TBM CPU TRANSLATION BUFFER MATRIX
- M8223 IRC CPU INSTRUCT DECODE and CLOCKS
- M8224 IDP CPU INSTRUCTION DATA PATH
- M8225 DBP DATA PATH B
- M8226 DEP DATA PATH E
- M8227 DDP DATA PATH D
- M8228 DCP DATA PATH C
- M8229 DAP DATA PATH A
- M8230 CEH CPU CONDITION CODE
- M8231 ICL CPU TRAPS AND INTERRUPT CONTROL
- M8232 CLK CPU CLOCK
- M8238 WCS KU780-A 2K WCS
- M8234 PCS KA780-A PCS, PROM CONTROL STORE
- M8235 USC MICRO SEQUENCE CONTROL
- M8236 CIB CONSOLE INTERFACE
VAX-11/782
The VAX-11/782, code-named Atlas, was a dual-processor VAX-11/780 introduced in 1982. Both processors shared
the same MA780 multi-port memory bus and the system operated asymmetrically, with the primary CPU performing all
I/O operations and process scheduling with the second, attached processor, only used for additional
computationally-intensive work. Effectively, this was two VAX-11/780s linked together to a shared memory cabinet.
For multistream computation-intensive tasks the system delivered up to 1.8 times
the performance of a VAX 11/780.
Personal experiences: at CAE Electronics we had 782s used for flight simulators. The shared memory was ideal for
sharing a common data set of flight variables that were accessed by programs running on each VAX. Two VAX systems and a shared memory cabinet
meant this occupied a large footprint at the data center. We had one VAX-11/780 installation for a simulator contract. One day the staff came in to find
that all the circuit boards were stolen, leaving only a shell of a system.
VAX-11/784
The VAX-11/784, code-named VAXimus, was a quad-processor variant of the VAX-11/780.
Similar to the VAX-11/782, it was an asymmetric multiprocessing system, with all four KA780 processors
sharing the same MA780 multi-port memory bus. Its performance was rated as 3.5 VUPS. This must
have had one large footprint as this was basically four VAX-11/780 computers connected through shared memory.
VAX-11/785
The VAX-11/785, code-named Superstar, was introduced in April 1984. Its KA785 CPU was essentially a
faster KA780, with a CPU cycle time of 133ns (7.52 MHz) versus the 200ns (5 MHz) CPU cycle time of the KA780,
giving a performance of 1.5 VUPS. The decrease in CPU cycle time was accomplished through use of higher speed Fairchild
Advanced Schottky TTL logic.
VAX-11/785 Modules:
- M7459 TRS, TERMINATOR & SILO
- M7460 KA785, SBL,CUP SBI LOW BITS
- M7461 KA785, SBH,SBI
- M7462 KA785, CAM, CACHE ADDRESS MATRIX
- M7463 KA785, CDM, CACHE DATA MATRIX
- M7464 KA785, TBM, CPU TRANSLATION BUFFER
- M7465 KA785, IDP, CPU INSTRUCTION DATA
- M7466 KA785, IRC, CPU INSTRUCTION DECODE
- M7467 KA785, DPB, CPU DATA PATH B
- M7468 KA785, DEP, CPU DATA PATH E
- M7469 KA785, DDP, CPU DATA PATH D
- M7470 KA785, DCP, CPU DATA PATH C
- M7471 KA785, DAP, CPU DATA PATH A
- M7472 KA785, CEW (CONDITION CODES, EXCEP)
- M7473 KA785, ICL (INTERRUPT CONTROL, LOW)
- M7474 KA785, CLK (CPU CLOCK)
- M7475 KA785, JCS, JOINT CONTROL STORE
- M7476 KA785, USC, MICRO SEQUENCER CONTROL
- M7477 KA785, CIB, CPU CONSOLE INTERFACE
Source: Text adapted from wikipedia.org.
VAX-11/780 Guides
VAX-11/785 Guides
| Document Name | Order Part No. | Publication Date | Domain |
|---|---|---|---|
| VAX-11/785 Hardware User's Guide | EK-11785-UG | 1984 | HW |
| 11785 Field Maintenance Print Set | NA | January 1985 | HW |
| KA785 Field Maintenance Print Set | NA | October 1983 | HW |
Sources: