UNIVAC 1218

Sperry Univac
Industry	Computer hardware
Headquarters	United States
Products	UNIVAC 418 series computers

The UNIVAC 418 was a transistor-based computer created by Sperry Univac, characterized by its 18-bit word length and magnetic-core memory technology. The designation "418" derived from its 4-microsecond memory cycle duration combined with the 18-bit word size. Programming for this system utilized the assembly languages TRIM III and ART418.

Throughout its production, over 392 units were manufactured across three different models. The design originated from the Control Unit Tester (CUT), which was initially developed to evaluate peripherals intended for larger computing systems.

Architecture

The instruction word was structured in three distinct formats:

Format I – Operations involving Load, Store, and Arithmetic functions

f - Function code (6 bits)
u - Operand address (12 bits)

Format II – Arithmetic constants and Boolean operations

f - Function code (6 bits)
z - Operand address or immediate value (12 bits)

Format III – Input/Output instructions

f - Function code (6 bits)
m - Minor function code (6 bits)
k - Designator (6 bits) used for specifying channel numbers, shift counts, etc.

Numerical data was represented using ones' complement notation, supporting both single and double precision floating-point formats. The TRIM assembly language employed octal numbering, which aligned well with the 18-bit word length divisible by three, rather than hexadecimal notation.

The processor included several addressable registers:

A - A 36-bit double precision Accumulator divided into AU (upper 18 bits) and AL (lower 18 bits)
ICR - Index Control Register (3 bits), also known as the "B-register"
SR - Special Register (4 bits), functioning as a paging register to facilitate access to memory banks beyond the currently active one
P - Program address register containing 15 bits

Register contents were visible in binary format on the front panel in real time, with push-button input available when the machine was halted.

UNIVAC 418-I

The initial UNIVAC 418-I model was delivered in June 1963, offering memory capacities ranging from 4,096 up to 16,384 words.

UNIVAC 1218 Military Computer

A military adaptation of the 418-I was marketed as the UNIVAC 1218, standing nearly six feet tall and weighing . This variant required power sources of both 115VAC single-phase at 60 Hz and 115VAC three-phase at 400 Hz.

System/component	Price
Minimum configuration: 1218 computer with 4,096 words of memory and 4 I/O channels	$96,000
Most typical configuration: 1218 computer with 16,384 words of memory and 8 I/O channels	$127,000
Militarized magnetic tape subsystem (2 tape handlers)	80,500
Paper tape subsystem including keyboard and printer	25,000
High-speed printing system	77,500
80-column card reader/punch system	83,250
	——————
Total price for minimum configuration of the 1218 computer system	$362,250
Total price for most common configuration of the 1218 computer system	$393,250

UNIVAC 418-II

Introduced in November 1964, the UNIVAC 418-II featured memory sizes ranging from 4,096 to 65,536 words of 18 bits each and boasted a shortened cycle time of just 2 microseconds. Its military counterpart, designated UNIVAC 1219 ("Mk 152 Fire Control Computer"), was incorporated into the Navy’s Mk 76 missile fire control system to operate the AN/SPG-55 radar.

UNIVAC 418-III

Launched in 1969, the UNIVAC 418-III featured a significant memory expansion, increasing capacity from 32,768 to 131,072 words, along with an enhanced cycle time of 750 nanoseconds. This model introduced new instructions supporting floating-point calculations, binary-decimal data conversions, and block transfers of up to 64 words. Additionally, the SR register was upgraded to accommodate six bits.

Distinctive hardware capabilities such as buffer overflow interrupts and hardware-enabled buffer chaining facilitated efficient processing of high-speed serial character streams. Although the original 418 hardware became outdated by the 1990s, emulation continued in use—for example, at the California Department of Water Resources operating on a UNIVAC 1100/60 system. Among prominent users was London's Royal London Hospital, which acquired a UNIVAC 418-III in 1973.

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