My Second Computer Was An Apple II

My second computer was an Apple II but my first computer was a Univac 1108.

The UNIVAC 1108 was a mainframe computer introduced in 1964 that was known for its reliability and performance in scientific, business, and real-time applications. It was a key model in the UNIVAC 1100 series, featuring integrated circuits for faster register storage and supporting multiprocessor configurations (the 1108 II) for enhanced multitasking. The 1108 was widely used, with over 200 systems sold, and was capable of running multiple programs concurrently.

Technical specifications and improvements

Architecture: Part of the UNIVAC 1100 series with a 36-bit word length.
Technology: Utilized integrated circuits instead of the thin-film memory used in its predecessor, the 1107.
Speed: Faster than the 1107, partly due to smaller and faster core memory.
Key features: Introduced base registers and additional hardware instructions to allow for dynamic relocation of programs in memory and support multiprogramming.
Multiprocessing: The 1108 II model, or 1108A, was the first in the series to support multiple processors, allowing it to handle multiple tasks simultaneously.

The Univac 1108 did not use 8-bit bytes, that came later

The UNIVAC 1108 did not use 8-bit bytes as its primary character addressing unit; its basic addressable unit (word size) was 36 bits. However, the architecture was flexible and could accommodate various sub-word fields for character data:

It could store six 6-bit FIELDATA characters per word.
It could also handle four 9-bit characters, the right-most eight bits of which were used for the ASCII code.
The concept of an 8-bit byte as the fundamental, universally addressable memory unit (which became standard with the IBM System/360, released around the same time in the mid-1960s) was not the native architecture of the 1108. The UNIVAC 1108 was a word-addressed machine with a 36-bit word length.

CPUs and Multiprocessing

The UNIVAC 1108 multiprocessor systems (known as the UNIVAC 1108 II or 1108A) were designed as a true general-purpose multiprocessing architecture, allowing for significant expansion and performance improvements over the single-processor version.

Key Features of Multiprocessor Configurations

Up to Three CPUs: The standard maximum configuration offered to customers included up to three Central Processing Units (CPUs).
Shared Memory: All processors in the system shared a common main memory, which was expandable up to 262,144 words (four 65K-word cabinets).
Multi-Module Access: A key component was the Multi-Module Access Unit (MMAU), which provided an eight-ported interface to the memory, allowing multiple CPUs and I/O controllers to access memory simultaneously with minimal conflict. This ability to access memory in an interleaved manner significantly increased throughput.
Dedicated I/O Controllers (IOCs): The system could also include up to two Input/Output Controllers (IOCs). These were separate processors dedicated to handling I/O functions, freeing the main CPUs to focus on computation.
Parallel Operations: A fully expanded system (three CPUs and two IOCs) could have up to five different activities occurring concurrently: three programs executing instructions in the CPUs and two I/O processes handled by the IOCs.
Operating System Support: The sophisticated EXEC 8 operating system was designed to manage the complexities of the multiprocessor environment, handling job scheduling, resource allocation, and “fail-soft” operations (the ability to continue running if one processor failed).
True Multiprocessing: Unlike some systems where one processor was a master and others were slaves, all CPUs in the 1108 II were considered equal, a hallmark of a true multiprocessor system. A “test-and-set” instruction was added to the instruction set to provide synchronization between the processors.
Special Configuration: While the standard maximum was three CPUs, one unique system with four CPUs was installed at United Airlines, though this specific configuration was not a generally available product.

Resources & References

Univac 3rd Generation Computers

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