【Mitsubishi Electric】 MELCOM 3100 Series

As computers entered the 3rd generation, the focus turned to the general applicability of software -- as exemplified by the IBM System/360 -- and the industry caught on to the idea of "family series" where the same software could be shared over multiple models.

The MELCOM 3100 series took advantage of this family configuration concept. Announced in 1966, the series consisted of three models — the Model 10, the Model 30, and the Model 50 — that offered expandable performance and capacity on a building-block principle. Along with creating this series, Mitsubishi Electric also introduced the concept of a standard interface so that all compatible peripherals could connect to any model. The standard interface made it possible for clients to construct the most suitable computer system for their application. Cycle stealing was used for reading and writing data to memory, which made it possible to perform up to 11 I/O operations in parallel with arithmetic processing.

Mitsubishi Electric developed a tape operating system and a disc operating system for the series that provided various compilers, assemblers, and other utility programs. This software was completely compatible with the MELCOM 1530.

The main specifications of the MELCOM 3100 series machines are given below.

MELCOM 3100 series
Main memory Capacity 8K to 32K words
Word length 18 bits (three-character length)
Cycle time 1.75μs
CPU Data formats Characters (variable length)
Decimal numbers (1 to 30 digits)
Binary numbers (18 bits and 36 bits)
Floating-point binary numbers (36 bits and 54 bits)
Instruction word length Variable length
Instruction methods 1 address, 2 addresses, 3 addresses, indexed addressing, indirect addressing
No. of instructions 155
Computation speeds Computation speeds Addition and subtraction: 35 μs
Multiplication: 201 μs
Division: 473.5 μs
18-bit fixed-point binary numbers Addition and subtraction: 3.5 μs
Multiplication: 15.75 μs
Division: 15.75 μs
Single precision floating-point numbers Addition and subtraction: 80.5 μs
Multiplication: 129.5 μs
Division: 181 μs
Main peripherals Magnetic tape units (20K to 120K characters/second)
Magnetic tape units (20K to 120K characters/second)
Magnetic disk pack unit (7,250K characters)
Magnetic drum unit (750K characters)
Card readers (800 cards/minute, 1,650 cards/minute)
Card punchers (250 cards/minute, 150 cards/minute)
Line printers (1,000 lines/minute, 600 lines/minute)
Paper tape readers (1,200 characters/second, 400 characters/second)
Paper tape punchers (120 characters/second, 25 characters/second)

MELCOM 3100 series