The Massbus is a high-performance

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

input/output In computing, input/output (I/O, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals ...

bus A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...

designed in the 1970s by

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...

(DEC). The architecture development was sponsored by Gordon Bell and John Levy was the principal architect. The bus was used by Digital to interconnect its highest-performance computers with

magnetic disk Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is ac ...

and

magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magne ...

storage equipment. The use of a common bus was intended to allow a single controller design to handle multiple peripheral models, and allowed the

PDP-10 Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...

PDP-11 The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were sold, ...

, and

VAX VAX (an acronym for Virtual Address eXtension) is a series of computers featuring a 32-bit instruction set architecture (ISA) and virtual memory that was developed and sold by Digital Equipment Corporation (DEC) in the late 20th century. The V ...

computer families to share a common set of peripherals. At the time there were multiple

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s for each of the 16-bit, 32-bit, and 36-bit computer lines. The 18-bit

PDP-15 The PDP-15 was the fifth and last of the 18-bit minicomputers produced by Digital Equipment Corporation. The PDP-1 was first delivered in December 1959 and the first PDP-15 was delivered in February 1970. More than 400 of these successors to th ...

/40 connected to Massbus peripherals via a PDP-11 front end. An engineering goal was to reduce the need for a new driver per peripheral per operating system per computer family. Also, a major technical goal was to place any magnetic technology changes (data separators) into the storage device rather than in the CPU-attached controller. Thus the CPU I/O or memory bus to Massbus adapter needed no changes for multiple generations of storage technology. A business objective was to provide a subsystem entry price well below that of IBM storage subsystems which used large and expensive controllers unique to each storage technology and processor architecture and were optimized for connecting large numbers of storage devices. The first Massbus device was the RP04, based on

Sperry Univac UNIVAC (Universal Automatic Computer) was a line of electronic digital stored-program computers starting with the products of the Eckert–Mauchly Computer Corporation. Later the name was applied to a division of the Remington Rand company and ...

Information Storage Systems's (ISS) clone of the IBM 3330. Subsequently, DEC offered the RP05 and RP06, based on

Memorex Memorex Corp. began as a magnetic tape, computer tape producer and expanded to become both a consumer media supplier and a major IBM plug compatible peripheral supplier. It was broken up and ceased to exist after 1996 other than as a consumer ele ...

's 3330 clone. Memorex modified the IBM compatible interface to DEC requirements and moved the data separator electronics into the drive. DEC designed the rest which was mounted in the "bustle" attached to the drive. This set the pattern for future improvements of disk technology to double density 3330, CDC SMD drives, and then "Winchester" technology. Drives were supplied by ISS/Univac, Memorex, and Control Data. Multiple generations of tape technology and performance were also Massbus connected although the architecture was a Master Massbus drive and slave tape drives. DEC also developed the Massbus RS03/04, a head per track disk drive for high performance swapping. The last Massbus disk drive was the DEC designed RM80 as DEC shifted to internal development of large disks.

Logical implementation

The bus is logically implemented as two separate sections: * An asynchronous control bus used to access

memory-mapped I/O Memory-mapped I/O (MMIO) and port-mapped I/O (PMIO) are two complementary methods of performing input/output (I/O) between the central processing unit (CPU) and peripheral devices in a computer. An alternative approach is using dedicated I/O pro ...

registers in the individual storage devices, and * A high-speed, synchronous data bus that is used to carry the actual data transfers between the storage devices and the host bus adapter. The data bus is 18 bits wide plus parity.

Massbus peripherals

Disk

* RP04 88 MB

Information Storage Systems pack-loaded (removable) disk drive * RP05/RP06 100/200 MB

677-51/677-01 pack-loaded (removable) disk drive The RP04 and RP06 disks were comparable to the 100 Mb

IBM 3330 IBM manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive (HDD) and floppy disk drive (FDD) were invented by IBM and as such IBM's employees were responsible fo ...

Mod I and IBM's 200 Mb Model II thereof. The 100 Mb RP05 was designated as "high performance" compared to the RP04.EK-DEC20-SP-002 * RP20 - 1.2Gb (non-removable) * RMxx disk drives: ** RM02/03/05/80 * RS03/RS04 head per track disks

Tape

* TU45 9 track, capable of 800 BPI and 1600 BPI; 120,000 bytes/second * TU78/TA78 6250 GCR The 1600/6250 BPI TU78 uses DEC's Massbus, whereas the TA78 uses the HSC50

controller Controller may refer to: Occupations * Controller or financial controller, or in government accounting comptroller, a senior accounting position * Controller, someone who performs agent handling in espionage * Air traffic controller, a person ...

Massbus CPU interfaces

* RH11—To the PDP-11's

Unibus The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon B ...

* RH750—To the VAX-11/75x bus

References

{{computer bus computer buses DEC hardware