UNIVAC III
Encyclopedia
The UNIVAC III, designed as an improved transistorized
replacement for the vacuum tube
UNIVAC I
and UNIVAC II
computers, was introduced in June 1962. It was designed to be compatible for all data formats. However the word size and instruction set were completely different; this presented significant difficulty as all programs had to be rewritten, so many customers switched to different vendors instead of upgrading existing UNIVACs.
The system was engineered to use as little core memory as possible, as it was a very expensive item. They used a memory system which had 25 bits width, and could be configured with from 8,192 words to 32,768 words of memory. Memory was built in stacks of 29 planes of 4,096 cores: 25 for the data word, 2 for "modulo-3 check" bits, and 2 for spares. Each memory cabinet held up to four stacks (16,384 words).
It supported the following data formats:
Instructions were 25 bits long.
The CPU had 4 accumulators, a 4 bit field (ar) allowed selection of any combination of the accumulators for operations on data from 1 to 4 words in length. For backward compatibility with the UNIVAC I and UNIVAC II data; two accumulators were needed to store a 12-digit decimal number and three accumulators were needed to store a 12-character alphanumeric value. When accumulators were combined in an instruction, the sign bit of the Most Significant Accumulator was used and the others ignored.
The CPU had 15 index registers, a 4 bit field (x) allowed selection of one index register as the base register. Operand addresses were determined by adding the contents of the selected base register and the 10 bit displacement field (m). Instructions that modified or stored index registers used a 4 bit field (xo) to select that index register.
Indirect addressing or field selection was selected if the 1 bit field (i/a) was set. Both indirect addressing and a base register could be selected in the indirect address in memory. Only a base register could be selected in the field selector in memory.
Sperry Rand began shipment in June 1962 and produced 96 UNIVAC III systems.
The operating systems(s) which were developed for the UNIVAC III's were called CHIEF, and BOSS. The largest number of UNIVAC III systems were equipped with tape drives, so tapes contained images of the system data at the head of any tape, followed by data. The OS could handle jobs at this time, so some tapes had data relating to job control, and others had data. UNIVAC III systems could have up to 32 tape drives.
Some systems were equipped at a later time with FASTRAND
drum, as the original design with only tape drives was found to be a drawback.
Transistor computer
A transistor computer is a computer which uses discrete transistors instead of vacuum tubes. The "first generation" of electronic computers used vacuum tubes, which generated large amounts of heat, were bulky, and were unreliable. A "second generation" of computers, through the late 1950s and...
replacement for the vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
UNIVAC I
UNIVAC I
The UNIVAC I was the first commercial computer produced in the United States. It was designed principally by J. Presper Eckert and John Mauchly, the inventors of the ENIAC...
and UNIVAC II
UNIVAC II
The UNIVAC II was an improvement to the UNIVAC I that UNIVAC first delivered in 1958. The improvements included core memory of 2000 to 10000 words, UNISERVO II tape drives which could use either the old UNIVAC I metal tapes or the new PET tapes, and some of the circuits were transistorized...
computers, was introduced in June 1962. It was designed to be compatible for all data formats. However the word size and instruction set were completely different; this presented significant difficulty as all programs had to be rewritten, so many customers switched to different vendors instead of upgrading existing UNIVACs.
The system was engineered to use as little core memory as possible, as it was a very expensive item. They used a memory system which had 25 bits width, and could be configured with from 8,192 words to 32,768 words of memory. Memory was built in stacks of 29 planes of 4,096 cores: 25 for the data word, 2 for "modulo-3 check" bits, and 2 for spares. Each memory cabinet held up to four stacks (16,384 words).
It supported the following data formats:
- 25 bit signed binary numbers
- excess-3Excess-3Excess-3 binary-coded decimal ' or Stibitz code, also called biased representation or Excess-N, is a complementary BCD code and numeral system it is used on some older computers that uses a pre-specified number N as a biasing value. It is a way to represent values with a balanced number of positive...
binary coded decimal with 4 bits per digit, allowing 6 digit signed decimal numbers - alphanumerics with 6 bits per character, allowing 4 character signed alphanumeric values
| 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| s | binary value (one's complement) | |||||||||||||||||||||||
| s | digit (XS-3) | digit (XS-3) | digit (XS-3) | digit (XS-3) | digit (XS-3) | digit (XS-3) | ||||||||||||||||||
| s | character | character | character | character | ||||||||||||||||||||
Instructions were 25 bits long.
| 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| i/a | x | op (opcode) | ar/xo | m (address) | ||||||||||||||||||||
The CPU had 4 accumulators, a 4 bit field (ar) allowed selection of any combination of the accumulators for operations on data from 1 to 4 words in length. For backward compatibility with the UNIVAC I and UNIVAC II data; two accumulators were needed to store a 12-digit decimal number and three accumulators were needed to store a 12-character alphanumeric value. When accumulators were combined in an instruction, the sign bit of the Most Significant Accumulator was used and the others ignored.
The CPU had 15 index registers, a 4 bit field (x) allowed selection of one index register as the base register. Operand addresses were determined by adding the contents of the selected base register and the 10 bit displacement field (m). Instructions that modified or stored index registers used a 4 bit field (xo) to select that index register.
Indirect addressing or field selection was selected if the 1 bit field (i/a) was set. Both indirect addressing and a base register could be selected in the indirect address in memory. Only a base register could be selected in the field selector in memory.
| 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| i/a | x | 0 | 0 | 0 | spare | l (address) | ||||||||||||||||||
| 0 | x | left bit (1..24 XS-3) | right bit (1..24 XS-3) | m (address) | ||||||||||||||||||||
Sperry Rand began shipment in June 1962 and produced 96 UNIVAC III systems.
The operating systems(s) which were developed for the UNIVAC III's were called CHIEF, and BOSS. The largest number of UNIVAC III systems were equipped with tape drives, so tapes contained images of the system data at the head of any tape, followed by data. The OS could handle jobs at this time, so some tapes had data relating to job control, and others had data. UNIVAC III systems could have up to 32 tape drives.
Some systems were equipped at a later time with FASTRAND
FASTRAND
FASTRAND was a magnetic drum mass storage system built by Sperry Rand Corporation for their UNIVAC 1100 series and 490/494 series computers.A voice coil actuator moved a bar containing multiple single track recording heads, so these drums operated much like moving head disk drives with multiple...
drum, as the original design with only tape drives was found to be a drawback.
External links
- UNIVAC III Data Processing System "A Third Survey of Domestic Electronic Digital Computing Systems" Report No. 1115, March 1961 by Martin H. Weik, published by Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland (at that time the computer was not yet available, 25 systems were on order and the time required for delivery was 18 months after placing the order)
- The UNIVAC III Computer
- UNIVAC III Photos
- UNIVAC III installations (serial numbers given where known)
- UNIVAC III Documentation (PDF) on bitsavers.org