The focus here is on technological developments in microcomputer operating systems from the late 1970s to the mid-1980s, deliberately excluding larger systems such as workstations and contemporary minicomputers. Another key topic is the external computer bus of this era. While operating systems served as the launching point for third-party software vendors, the bus could be considered the primary hardware interface to the computer. Although there were parallel and serial interfaces, the bus was more fundamental because it allowed for the creation of virtually any peripheral, including cards for serial and parallel ports.
This discussion does not delve into the contemporary processors and their complex histories. Additionally, it overlooks economic considerations, market dynamics, strategic decisions, and other factors in the broader context.
In retrospect, PC-DOS / MS-DOS emerged victorious, with the IBM PC becoming the new de facto standard in this market. The well-documented story of how and why this happened is widely known. However, in the periphery, intriguing developments were stifled, potentially escaping broader historical narratives. Some examples here will shed light on traces of that overlooked story.
In the late 1970s and early 1980s, many contemporary computer manufacturers expanded their proprietary solutions by incorporating CP/M1 capabilities, either through add-on cards or by redesigning their machines. This trend emerged as CP/M gained market traction. For instance, the Apple II could run CP/M software using third-party Z80 processor cards, such as the Microsoft SoftCard.2 Similarly, the Commodore 128 included a Z80 processor, enabling it to run CP/M alongside its native operating systems.3
Additionally, some systems came with CP/M pre-installed from the start. Notable examples include the Osborne 14, an early portable computer that bundled software like WordStar5 and SuperCalc6, and the Kaypro II7. These integrations highlighted CP/M's versatility and widespread adoption during that era.
Not to be unfashionable, the ABC802 did also came prepared for a possible extension of running CP/M.8
Developed by Gary Kildall9 (Digital Research Inc.)10, CP/M (Control Program for Microcomputers, Control Program / Monitor) is one of the seminal operating systems in the history of personal computing. CP/M began in 1973 when Gary Kildall wrote the initial version to run on Intel 8080/85-based microcomputers. Officially released in 1974, CP/M quickly became one of the first widely used de facto operating systems for personal computers.
In the pre-CP/M era, early microcomputers lacked standardised operating systems. Probably it could not be fitted in them, often low on memory. Sometimes they had though "monitors," early basic communications with the system for debugging, status etc. Users often had to write their own software to interact more directly with the hardware, which was naturally a significant barrier to wider adoption and usability. By providing a de facto standardised operating system that could run on various hardware platforms, CP/M played a pivotal role in the growth of the personal computer market during the late 1970s and early 1980s. It enabled software developers to write programs that could be distributed widely and run on a variety of machines, paving the way for a burgeoning software industry.
CP/M featured a simple, yet effective file system and command-line interface, which was user-friendly for its time. One significant strength was its design, which made it easily adaptable to various hardware platforms. This portability was a crucial factor in its widespread use. CP/M utilised a BIOS11 (Basic Input/Output System) to handle hardware-specific operations. This abstraction layer enabled the operating system to run on different machines with minimal modifications, enhancing its portability and flexibility. The BIOS is also one of the features that translated well to the future MS-DOS era.
CP/M fostered a rich ecosystem of software applications and development tools. Popular software like WordStar was first developed for CP/M, and a successful database management dBASE II12 became very popular software ported to CP/M. Microsoft's MS-DOS, later on became the standard operating system for IBM PCs, was heavily influenced by CP/M. The initial version of MS-DOS (also known as 86-DOS or QDOS) was even designed to be 'compatible' with (legacy) CP/M-86 software, facilitating an easier transition for users and developers. Its interactive command-line featured many familiar commands. Portability was easier when APIs were close enough for a smoother transition. This included compatibility with CP/M’s BIOS and BDOS (Basic Disk Operating System) calls, which were mapped to equivalent functions in MS-DOS.
On the hardware side, there was also a similar standardisation development. The S-100 bus,13 originally known as the Altair bus, was introduced in 1974 with the MITS Altair 8800,14 one of the first commercially successful personal computers. Initially designed for the Intel 8080 microprocessor, it was later adapted for other processors, including the Zilog Z80 and the Intel 8085. The bus consisted of a 100-pin edge connector, providing a standardised interface for attaching CPU, memory, and peripheral cards. Users could easily add or replace components to upgrade their systems, which promoted a thriving third-party hardware market. The standardisation of the bus allowed components from different manufacturers to work together.
It is important to note that CP/M and the S-100 bus were not dependent on each other. They were distinct standards, each contributing independently to the diverse and evolving personal computer market. These unifications highlighted the significance of a common ground. However, identifying where that intersection lay and how to achieve it remained an unresolved challenge.
The rise of CP/M and the S-100 bus standard occurred roughly in the same time span, creating a synergistic environment where microcomputer users could benefit from a standardised software platform CP/M and a standardised hardware interface S-100. This combination contributed to the growth of the personal computer industry by making it somewhat easier for users to expand and customise their systems and for developers to create compatible hardware and software.
But eventually these standards had their drawbacks, as time progressed. The S-100 bus large and complex backplanes and cards made systems bulky and costly to design and maintain. The parallel bus architecture was prone to electrical noise and signal integrity issues, leading to potential data corruption and system instability, as more cards were added. High power consumption due to its wide range of supported voltages required robust power supplies and cooling solutions, further increasing costs. Despite being a standard, variations in implementation among manufacturers caused compatibility issues. The bus also suffered from relatively slow data transfer speeds, becoming a performance bottleneck. Additionally, the connectors were not robust, leading to mechanical issues and the need for frequent maintenance. As newer, more efficient bus standards like the ISA (internal 16-bit of IBM PC/AT) emerged, the S-100 bus quickly became outdated, struggling to keep up with evolving hardware capabilities.15
CP/M, originally designed for 8-bit microprocessors, had several drawbacks that limited its effectiveness as computing technology advanced. Its memory management capabilities were restricted, allowing it to address only up to 64KB of memory. The absence of built-in networking capabilities hindered its usefulness in networked environments, becoming a significant limitation as businesses and individuals began connecting computers in local area networks (LANs) and using modems for remote communication -- although there were applications running e.g. terminal emulations. CP/M's command-line interface, though functional, was basic and started to feel outdated as graphical user interfaces like those in e.g. the Apple Macintosh and later Microsoft Windows emerged, offering more intuitive and visually appealing experiences. Additionally, CP/M struggled to support emerging hardware technologies such as high-resolution graphics, advanced sound systems, and sophisticated input devices, making it less appealing for multimedia applications. Its single-tasking nature, which allowed only one program to run at a time, became a significant drawback as multitasking grew in importance for productivity and user convenience. Furthermore, the existence of many variations of CP/M created by different hardware manufacturers led to compatibility issues, with software written for one version often not running correctly on another. These limitations collectively contributed to CP/M's decline as a previous dominant operating system.
IBM’s decision to use MS-DOS for its PCs was a major blow to CP/M. IBM PCs quickly became the industry standard, and MS-DOS emerged as the dominant operating system. It is important to note that IBM also offered CP/M and UCSD Pascal as alternatives to MS-DOS, but the pricing for CP/M was significantly higher. The saying 'You couldn't go wrong with buying an IBM,' originally used when considering mainframes, underscored the reliability and growing popularity of the IBM PC. Even though PC-DOS / MS-DOS was built on a 'clone' of CP/M, it evolved and laid the foundation for a large developer market.
This shift fostered a competitive software market for PCs, which established a standard in both hardware and software. Previously, proprietary computer brands with unique solutions had competed for dominance. While early de facto standards here provided some cohesion, their future impact was limited.
In 1974, i.e. the same year of birth as the S-100, the Data Board 4680 system was designed by Dataindustrier AB16 with support for three microprocessors: Intel 4004, Motorola 6800, and Intel 8080. Other additional processors were initially considered for use, and also cards were built, but ultimately, the Z80 became the predominant choice. This original system consisted of a CPU card, and separate cards for RAM and EPROM for software. The 4680 bus featured a 16-bit address bus and an 8-bit data bus, allowing it to directly address 64 KB of memory.
The modular system was used in various applications such as a diagnostic machine for brain tumors at a prominent hospital, the printing process at a major newspaper, or a control system for an industrial manufacturer in collaboration with an automation company.
In 1977, the 7S (Seven S) debuted as a combined monochrome terminal and computer utilizing the Data Board 4680 bus and powered by the Z80 processor. Following this, in 1978, the ABC80 was introduced as a Z80-based monochrome home computer, also with a variation as the "ABC-bus", which could connect to Data Board 4680.
By 1981, the ABC800 emerged as an enhanced model for both office and home use, equipped with 32 KB of RAM and featuring color graphics. And as we know, in 1983 the ABC802 was launched as a variant of the ABC 800, offering 64 KB of RAM, with 32 KB designated for use as a RAM disk. Or the alternative use: as a 64 KB CP/M machine. Further enhancing the lineup was the ABC806, which featured 160 KB of RAM, with 128 KB allocated as a RAM disk. Also with enhanced graphics. All of these computers were in fact based on the Data Board 4680 bus.
But Data board 4680 represented more of a niche approach to microcomputer design, focusing on specific industrial and computing needs rather than aiming for broad consumer appeal. Its influence was felt in specialized applications but obviously did not have the same widespread impact as the S-100.
Data Board 4680 was employed in embedded control applications. This could include industrial automation, where precise timing and control were necessary, leveraging the capabilities of primarily the Z80 processor. In educational and experimental settings, the Data Board 4680 provided a platform for early computing enthusiasts and hobbyists to explore different microprocessor architectures. Certain specialized computing tasks, such as data acquisition systems or specific instrument control applications, benefited from the versatility. Engineers and scientists could customize systems based on their specific requirements.
The designer of the basis for the ABC-line of computers and the Data Board 4680, was in the main Lars Karlsson, together with a group of engineers. A self-taught engineer, Karlsson early on realise the importance of the "bus"17 but also the abstraction or generalisations of the "bus". But as technology progressed, the bus also had to change. When 16-bit processors came along, and Unix became a topic of interest, the bus also had to adapt. Dataindustrier AB, alternatively called by the acronym DIAB AB later, started by Karlsson in 1971, became one of Swedens primary designer for microcomputers. No other company nationally made such a success in this market with their own design. Lars Karlsson left Sweden for USA in 1983, to focus on Data Board 4680 and the future, but also then sold shares of the company he once started.
Computer manufacturers in the beginning of 1980s faced critical decisions about their future direction. The importance of the 1981 IBM PC was evident, but the extent of its impact and the direction of the market were uncertain. Key questions included: Where was the technology heading? How crucial was legacy support? How could the company stay relevant in the changing technological landscape?
Business as Usual: Some manufacturers adopted a "business as usual" approach, assuming that their customers would remain satisfied with whatever they produced and innovated. This group often targeted the low-end market, where affordability and entertainment, such as gaming, were key factors. They produced cheaper computers that fit well within this (rather large) niche.
Partial Compatibility: Another group chose to create "clones" of the IBM PC with a twist. These manufacturers, including local and national companies like Nokia and Ericsson, made PCs that were not fully compatible with the original IBM PC. They aimed to offer a superior product by adding unique features or improvements, hoping for customer loyalty. However, they often miscalculated the market risks and faced high costs, which led to their decline within a few years.
Full Compatibility: The third group understood the critical importance of full compatibility with the IBM PC. They focused on reverse engineering, including replicating the BIOS, to ensure that their PCs were entirely compatible with IBM PCs. This approach allowed them to capitalize on the existing software ecosystem and meet the demands of users who required seamless compatibility. Companies like Compaq successfully adopted this strategy, becoming significant players in the market by offering reliable IBM PC clones.
But there was at least one group more: they bet on UNIX as the future.18
Unix was developed in the late 1960s and early 1970s at AT&T's Bell Labs by Ken Thompson, Dennis Ritchie, and some others. That is years before CP/M. Initially, it was a small, flexible operating system for the prevalent and current minicomputers (most famously the PDP-11). Thus it was aimed at significantly different computers than CP/M. But Unix quickly gained popularity in academic and research institutions due to its portability, powerful features, and the availability of its source code for educational purposes.
In the late 1970s, AT&T began licensing Unix to commercial vendors, which led to a proliferation of Unix versions. Different vendors developed their own variants, leading to extreme fragmentation.
One significant variant was the Berkeley Software Distribution (BSD), developed at the University of California, Berkeley. BSD introduced many enhancements and became a foundation for later Unix systems. But they also had license fees to be paid to AT&T for some Unix software. A significant difference at the start was that important networking such as TCP/IP was supported on BSD, but only later added to the AT&T versions.
In the years to come, overcoming fragmentation was a significant issue, perhaps the largest of them all. Besides technological challenges, licensing restrictions and the use of the Unix brand also hindered companies, development, and market expansion.
In 1983, same year as Luxor introduced ABC802, DIAB developed its first UNIX-compatible machine, the DIAB DS90, using the Motorola 68000 CPU. They initially used a UNIX System V license from AT&T, but being an industrial automation company, DIAB required a real-time operating system. To meet this need, they replaced the AT&T-supplied UNIX kernel with their own real-time variant. Over time, DIAB also developed their own versions of UNIX standard tools, eventually eliminating any code derived from UNIX. This allowed DIAB to deploy their machines independently, without needing an AT&T UNIX license. But not being able to use the UNIX brand, of course,
Two years later, DIAB continued enhancing the DS90 computer series, incorporating newer Motorola CPUs such as the 68010, 68020, 68030, and the 68040. Luxor was offered to sell a DS90 as they rebranded "ABC9000", and the operating *NIX called D-NIX, was instead rebranded as "ABCenix".19 Also a smaller model called ABC1600 run the same OS.20 This latter system D-NIX was even licensed or possibly only rebranded as Cromix for Cromenco.21 D-NIX and the computers from DIAB continued to live under a new ownership of Bull in the 1990s. They sold OEM solutions to other companies, e.g. Norsk Data.
Here somewhere in the mid 1980s was the beginning of what to become the "Unix wars."22. It was a period of competition and fragmentation continuing from the mid 80s into the 1990s. This era was characterized by disputes among various Unix vendors and standards bodies, leading to the proliferation of different Unix variants and standards.
But there were some achievements in standardization efforts such as POSIX and somewhat of the Single UNIX Specification (SUS). However, rivalry among vendors, intense competition, legal disputes over licensing, and ongoing compatibility issues continued to pose significant challenges. Competition often led to proprietary extensions, which further contributed to fragmentation.
That history, however, extends far beyond the lifespan of the ideas surrounding the ABC802 and its relatives.
Appendix: CP/M, Unix, MS-DOS/PC-DOS23
CP/M: Designed for microcomputers using Intel 8080 or Zilog Z80 processors, aimed at hobbyists, small businesses, and early personal computer users.
Unix: Initially designed for minicomputers and mainframes used by researchers, academics, and enterprise environments. Early Unix required more powerful hardware compared to CP/M.
MS-DOS/PC-DOS: Designed for IBM PCs and compatible microcomputers using Intel x86 processors, aimed at personal and business users.
CP/M: Simple, single-tasking operating system with a command-line interface.
- File System: Utilised a flat file system with an 8.3 filename convention (eight characters for the name, three for the extension).
- Memory Management: Limited to 64 KB of RAM, reflecting the hardware constraints of early microcomputers.
- Modularity: Relied on a system BIOS to handle hardware-specific functions, requiring customization for different hardware.
Unix: Multiuser, multitasking operating system with a hierarchical file system.
- File System: Supported long filenames and a complex directory structure. Utilised a hierarchical file system with nested directories.
- Memory Management: More advanced memory management, supporting larger amounts of RAM and virtual memory.
- Modularity: Designed to be highly portable across different hardware platforms. Unix was written in C, which facilitated easier adaptation to various systems.
MS-DOS/PC-DOS: Single-tasking operating system with a command-line interface.
- File System: Initially used the FAT12 file system, which also had an 8.3 filename convention. Later versions supported FAT16 and FAT32.
- Memory Management: Initially limited to 640 KB of conventional memory, with later enhancements for extended and expanded memory.
- Modularity: Less modular compared to Unix but more standardised than CP/M, as MS-DOS was designed to run on IBM PCs and compatible with a standard BIOS interface.
CP/M: Command-line interface (CLI) with a simple set of commands.
- Usability: Geared towards users with some technical knowledge, but less complex than Unix. Limited user interface features compared to Unix.
Unix: Command-line interface with powerful shell scripting capabilities. Early Unix systems used shells like the Bourne shell (sh).
- Usability: More complex commands and utilities, providing greater power and flexibility but requiring more technical expertise. Unix systems often included a rich set of command-line tools and utilities.
- GUI: Some systems had some (proprietary) graphical interfaces, like D-NIX. Later on not uncommon with X-Windows.
MS-DOS/PC-DOS: Command-line interface (CLI) with a straightforward set of commands.
- Usability: Designed to be user-friendly for business and personal use, simpler than Unix but more advanced than CP/M in terms of user interface and available commands.
- GUI: MS-DOS/PC-DOS itself did not include a GUI, but it could run graphical environments like Microsoft Windows, which started out as an add-on (graphical shell) to MS-DOS.
CP/M
- Software: Had a significant library of early business and productivity software, including word processors, spreadsheets, and database programs.
- Ecosystem: Dominated the early microcomputer market before being overtaken by MS-DOS. Limited networking and multiuser capabilities.
Unix
- Software: Known for its rich set of development tools, including compilers, text processing utilities, and networking tools. Early Unix also supported multiuser environments and networked operations.
- Ecosystem: Widely used in academic, research, and enterprise environments. Unix systems contributed to the development of the Internet and networking protocols.
MS-DOS/PC-DOS
- Software: Initially focused on providing a command-line interface and basic system utilities. Over time, MS-DOS amassed a significant library of applications including early versions of Microsoft Word and Excel, as well as various business and gaming software.
- Ecosystem: Became dominant in the IBM PC-compatible market, eventually overtaking CP/M. MS-DOS lacked built-in networking and multiuser capabilities in its early versions, focusing primarily on single-user desktop computing.
CP/M
- Networking: Very limited networking capabilities. Primarily designed for standalone systems.
- Multiuser: Not designed for multiuser operation. Single-tasking environment.
Unix
- Networking: Strong networking capabilities, supporting early development of TCP/IP and networked computing.
- Multiuser: Designed from the ground up to support multiple users simultaneously. Included features like file permissions and process management to handle multiple users and tasks.
MS-DOS/PC-DOS
- Networking: Limited native networking capabilities in early versions. Networking support evolved over time with add-on software and later versions of DOS.
- Multiuser: Designed as a single-user operating system, lacking inherent multiuser capabilities. Later versions of DOS (like MS-DOS 5.0 and later) included features for multitasking and enhanced memory management, but true multiuser support was not a native feature.
CP/M
- Portability: Required a custom BIOS for each hardware platform, which limited its adaptability to new systems.
- Adaptability: Less portable compared to Unix. Each new hardware platform necessitated significant modifications.
Unix
- Portability: Highly portable due to being written in the C programming language. Unix could be adapted to run on a wide variety of hardware platforms.
- Adaptability: Designed to be easily modified and extended. Unix’s modular architecture and use of C made it easier to port and adapt to different environments.
MS-DOS/PC-DOS
- Portability: Relied heavily on hardware-specific drivers and configurations, tied closely to the IBM PC architecture. Compatibility across different hardware platforms was limited without significant modifications.
- Adaptability: Adapted primarily through OEM versions tailored for specific hardware configurations. Microsoft allowed OEMs to customize MS-DOS for their hardware, contributing to its widespread adoption on various PC clones. (Not unlike their experience with adaptability of MSBASIC.)
- Bit för bit med ABC 800, Luxor datorer, Motala, 1984.
- Lundgren, Jan & Thornell, Sören, BASIC II boken, 1. uppl., Emmdata, Umeå, 1982.
- Lundgren, Jan & Thornell, Sören, BASIC II boken för ABC 802, 1. uppl., Emmdata, Umeå, 1983.
- Zaks, Rodnay, CP/M handboken med MP/M, Pagina, Stockholm, 1982.
Footnotes
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Elementary on CP/M: https://en.wikipedia.org/wiki/CP/M. ↩
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Z80 SoftCard: https://en.wikipedia.org/wiki/Z-80_SoftCard. ↩
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Commodore 128: https://en.wikipedia.org/wiki/Commodore_128. ↩
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Osborne 1: https://en.wikipedia.org/wiki/Osborne_1. ↩
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WordStar: https://en.wikipedia.org/wiki/WordStar. ↩
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SuperCalc: https://en.wikipedia.org/wiki/SuperCalc. ↩
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Almost the same computer, CP/M for ABC800: https://www.abc80.net/archive/luxor/sw/CPM/MYAB-Bruksanvisning-for-cpm-pa-ABC800.pdf. Although here it was an addition, instead of pre-built harware. ↩
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Some technical principals of the contemporary bus and some of its problems can be read at: https://en.wikipedia.org/wiki/Bus_(computing)#Minis_and_micros ↩
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Among them were in fact Microsoft with Xenix. ↩
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https://sv.wikipedia.org/wiki/DIAB_Serie_90 https://www.abc80.net/archive/luxor/DS90/reklam/8506-DIAB-DS90-Multi-user-16-32-bit-supermicro-computer.pdf & https://www.abc80.net/archive/luxor/DS90/Ett-helt-nytt-systemt%c3%a4nkande-fr%c3%a5n-dataindustrier.pdf ↩
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This chapter has been derived from chatting with ChatGPT and other current LLMs. We chatted and came to this reasonable conclusion and summary of facts. Also some sources: CP/M https://en.wikipedia.org/wiki/CP/M & CP/M-86 https://en.wikipedia.org/wiki/CP/M-86, UNIX https://en.wikipedia.org/wiki/History_of_Unix, and MS-DOS https://en.wikipedia.org/wiki/MS-DOS & IBM PC DOS https://en.wikipedia.org/wiki/IBM_PC_DOS. ↩