Slide Rule, Minimum Latency Calculator for the UNIVAC Solid-State Computer
date: label: date made
content: ca 1960
name: label: maker
content: Remington Rand Univac
notes: label: Description
content: This circular device was an aid to programming the UNIVAC solid-state computer. It consists of a paper disc with equal divisions running from 1 to 200 near the edge, and a clear plastic rotating disc that are pivoted together at the center. The upper disc is marked in red with two perpendicular diameters. The solid state computer had a magnetic storage drum on which locations were specified numerically. The latency calculator allowed programmers to write code for the machine to make the most efficient possible use of the drum memory. The back of the instrument gives a list of instruction codes and corresponding word times. Recieved in bag. Reference: Sperry Rand Corporation, Programming: Simple Transition to Electronic Processing UNIVAC Solid-State 80, 18-26.
label: Description
content: Compare 2005.0271.01. Date based on date of documents 2015.3097.03 and 2015.3097.04.
label: Description
content: According to Kirk Lubbes, who programmed the Univac Solid State Computer:
label: Description
content: "The SS90 had a drum memory, i.e. memory was not random accessible. One had slow memory and fast memory. The slow memory had only a single read/write head per track on the drum and fast memory had four read/write heads spaced at 90 degrees, so therefore the drum had to rotate a full revolution to access a memory word in slow memory and only a quarter turn to access fast memory.
label: Description
content: The trick in programming the SS90 was to have the instruction and its operand accessible at an optimal time so that the instruction could access its operand without waiting for the drum very far. As one started a program, this was not much a problem. The programmer new how much time that a given instruction would take to execute and the speed of the drum. Therefore, he calculated the position of the next instruction, based these two parameters. The minimum latency calculator was a mechanical device to help in this calculation. The problem was that as the programmer progressed, collisions occurred, i.e. the optimal location of an instruction or an operand was already taken by a previous instruction or operand. Since the drum was arranged in bands and the read/write heads were at the same location on each band, if one had a collision, you could put the necessary instruction or operand in a parallel band at the same position. This worked the bands all filled up.
label: Description
content: The basic approach was to get a program working using the best latency that you could. Then the programmer would go back and start rearranging instructions and operand locations to achieve minimum latency. In those early times, machine time was expensive and memory severely limited. So it was important that production programs were efficient."
label: Description
content: Reference:
label: Description
content: Nonccession file 2015.3097.
label: Location
content: Currently not on view
place: label: place made
content: United States: New York, New York
setName: label: See more items in
content: Medicine and Science: Computers
label: See more items in
content: Computers & Business Machines
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content: Slide Rules
creditLine: label: Credit Line
content: Gift of R. Kirk Lubbes
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 2015.3097.01
label: nonaccession number
content: 2015.3097
label: catalog number
content: 2015.3097.01
objectType: label: Object Name
content: slide rule
physicalDescription: label: Physical Description
content: paper (base, bag material)
label: Physical Description
content: plastic (covering disc material)
label: Physical Description
content: metal (rivet material)
label: Measurements
content: overall: .1 cm x 14.5 cm x 14.5 cm; 1/32 in x 5 23/32 in x 5 23/32 in