What was CP/M and what was its primary function?

CP/M, which originally stood for Control Program/Monitor and later Control Program for Microcomputers, was a mass-market operating system created in 1974. Its primary function was to organize files on magnetic storage media and to load and run programs stored on a disk, serving as a disk operating system for microcomputers.

Who developed CP/M and for which processors was it initially designed?

CP/M was developed by Gary Kildall of Digital Research, Inc. It was initially designed for microcomputers based on the Intel 8080 and Intel 85 processors.

What were the core components of the CP/M operating system?

The core components of CP/M were the Basic Input/Output System (BIOS), the Basic Disk Operating System (BDOS), and the Console Command Processor (CCP). The BIOS handled hardware drivers, the BDOS managed the file system and provided system services, and the CCP acted as the command-line interpreter.

How did CP/M become a dominant operating system in the microcomputer market?

CP/M became the de facto standard and dominant operating system for microcomputers, particularly those using the S-100 bus, through the late 1970s and mid-1980s. Its widespread adoption was driven by its ability to reduce programming effort for porting applications to different hardware, thereby increasing the market size for both hardware and software.

What led to CP/M's eventual displacement in popularity?

CP/M's popularity was eventually displaced by DOS, particularly after the introduction of the IBM PC in 1981. The rise of IBM-compatible hardware and the success of MS-DOS led to CP/M's decline in market share.

What was the original meaning of the acronym CP/M?

The acronym CP/M originally stood for 'Control Program/Monitor', suggesting its role as a primitive resident monitor, a precursor to a full operating system. Later, it was officially registered as 'Control Program for Microcomputers'.

What influences shaped the design of CP/M?

Various aspects of CP/M were influenced by the TOPS-10 operating system used on DECsystem-10 mainframe computers, which Gary Kildall had experience with. Additionally, the naming convention followed trends set by IBM's CP/CMS and Kildall's own PL/M language.

How did Digital Research increase the licensing cost of CP/M?

Initially, Gnat Computers licensed CP/M for $90 in 1977. However, due to high demand within a year, Digital Research was able to increase the license cost to tens of thousands of dollars.

Who were some of the key developers involved in the early stages of CP/M?

Gary Kildall was the original developer. John Pierce was primarily responsible for the development of CP/M 2.0. Kathryn Strutynski was an early employee who debugged CP/M 2.0 and became a key developer for CP/M 2.2 and CP/M Plus. Robert "Bob" Silberstein and David "Dave" K. Brown were also early developers.

What made CP/M a 'software bus'?

CP/M was described as a 'software bus' because it provided a standardized way for multiple programs to interact with different hardware components. This abstraction layer significantly reduced the effort required to port applications to new computer systems.

What were some of the limitations of early CP/M versions regarding disk handling?

Early versions of CP/M, such as version 1.0, lacked a mechanism to detect if a disk had been changed. This could lead to data corruption if the system attempted to write to a new disk using the directory information of the previous disk. Later versions (1.1/1.2 onwards) would signal a fatal error instead, preventing overwrites but requiring a reboot.

How did CP/M facilitate software portability?

The core components of CP/M (BDOS, CCP, and transient commands) were consistent across different hardware configurations. By only needing to adapt the hardware-specific BIOS, manufacturers could support a wide range of existing CP/M software, making it easier for applications to run on various machines.

What was the significance of the CP/M-80 retronym?

When 16-bit versions like CP/M-86 were released, the original 8-bit CP/M became known by the retronym CP/M-80. This was done to distinguish it from the newer 16-bit versions and avoid confusion.

Why did CP/M-86 fail to become the standard for the IBM PC?

CP/M-86 was initially expected to be the standard for the IBM PC. However, Digital Research and IBM could not agree on development and licensing terms. IBM then turned to Microsoft, and the significantly lower price of Microsoft's PC DOS ($40 vs. $240 for CP/M-86) further deterred customers, preventing CP/M-86 from gaining dominance.

What was the purpose of the XLT86 tool?

XLT86 was a tool developed by Digital Research that translated assembly language source code from the Intel 8080 processor to the Intel 8086. This facilitated the porting of CP/M-80 applications to the CP/M-86 platform by optimizing the output and handling calling conventions.

How did MS-DOS borrow concepts from CP/M?

MS-DOS adopted several concepts from CP/M, including drive letters (A:, B:, etc.) and the 8.3 filename format. Its file-handling data structures were also identical, making it easier to port CP/M software.

What was the main innovation of MS-DOS compared to CP/M?

MS-DOS's main innovation was its File Allocation Table (FAT) file system. Additionally, it generally had access to more memory and built more commands into its command-line shell, making it faster and easier to use on floppy-based systems compared to CP/M.

What is ZCPR and what did it replace?

ZCPR, which stands for Z80 Command Processor Replacement, was introduced as a drop-in replacement for the standard Digital Research console command processor (CCP) in CP/M systems. It offered enhanced features and customization options.

What were some key features of ZCPR3?

As of version 3, ZCPR included features such as shells, aliases, I/O redirection, flow control, named directories, search paths, custom menus, passwords, and online help. It also had the capability to be compiled for 8080 processors with reduced features.

What were the minimum hardware requirements for a basic 8-bit CP/M system?

A minimal 8-bit CP/M system required a computer terminal with an ASCII character set, an Intel 8080, 8085, or Zilog Z80 microprocessor, at least 16 kilobytes of RAM starting at address 0, a means to bootstrap the first sector of a diskette, and at least one floppy disk drive.

How did manufacturers customize CP/M for their specific hardware?

Manufacturers customized CP/M by adapting the BIOS portion of the operating system to match their specific hardware configurations, including memory, disk drives, and console devices. This allowed the core OS components (BDOS, CCP) to remain consistent.

What was Personal CP/M?

Personal CP/M was a ROM-based version of the operating system developed by Digital Research in partnership with Zilog and American Microsystems. It was aimed at lower-cost systems and was described as being rewritten to take advantage of the enhanced Z-80 instruction set.

What is the Transient Program Area (TPA) in CP/M?

The Transient Program Area (TPA) was the read/write memory space in CP/M, typically located between hexadecimal address 0100 and the start of the BDOS. This area was available for CP/M application programs to load and execute.

What was DDT in CP/M?

DDT, short for Dynamic Debugging Tool, was a debugging utility included with CP/M. It was nicknamed 'DDT' after the insecticide, implying its function as a 'bug' killer, allowing users to examine, manipulate, and step through program execution.

Did CP/M originally support resident programs similar to DOS TSRs?

No, CP/M originally did not support the equivalent of Terminate and Stay Resident (TSR) programs as seen in DOS. However, programmers could intercept OS calls to extend functionality, and CP/M 3 introduced support for dynamically loadable Resident System Extensions (RSX).

What was the typical process for installing software on CP/M systems?

Software installation often involved running an installation program that adapted the application to specific hardware features, such as printers and terminals, usually through escape sequences. This process often needed to be repeated for each application, as CP/M lacked a centralized service for device management.

What was the standard 8-inch floppy disk format for CP/M?

The standard 8-inch floppy disk format for CP/M was based on the IBM System/34 and IBM 3740, featuring 128 bytes per sector, single density, and single-sided recording.

Why was there no standard 5.25-inch CP/M disk format?

There was no single standard 5.25-inch CP/M disk format because various manufacturers like Kaypro, Morrow Designs, and Osborne each used their own formats. This fragmentation required software distributors to support multiple formats, contributing to CP/M's eventual obsolescence.

How were files named in CP/M?

CP/M files followed an '8.3' filename format, consisting of up to eight characters for the name, followed by a period, and then up to three characters for the extension. The extension typically indicated the file type, such as '.COM' for executable programs or '.TXT' for text files.

How did CP/M handle file sizes?

File sizes were specified in terms of the number of 128-byte records (which corresponded to disk sectors on 8-inch drives) occupied by the file. There wasn't a standard way to specify exact byte counts, and text files conventionally used a Control-Z character (ASCII SUB) to mark the end of the file content.

What was the purpose of CP/M's user areas?

CP/M provided 16 numbered user areas (0-15) to organize files on a disk, as it lacked subdirectories. This feature was intended to provide some compatibility with multi-user MP/M systems and help organize files, especially on hard drives, allowing different users or tasks to have their own file spaces.

Did CP/M have standardized graphics support?

CP/M did not offer standardized graphics support until the release of GSX (Graphics System Extension) in 1982. Due to memory constraints, graphics were not a common feature, and most systems relied on ASCII art or block graphics characters accessible through programming.

What were some popular applications originally developed for CP/M?

Popular applications that debuted on CP/M include WordStar (a word processor), dBase (a database program), VisiCalc (the first spreadsheet), SuperCalc (another spreadsheet), and AutoCAD (a CAD application). Many compilers and interpreters for languages like BASIC, FORTRAN, and PL/I were also available.

What was the 'end-of-file' convention for text files in CP/M?

Text files in CP/M were conventionally terminated with a Control-Z character (ASCII SUB, hexadecimal 1A). This character marked the end of the file's content, and its presence within the file could lead to truncation of data.

What was the inefficiency in CP/M's file allocation for small files?

With the introduction of larger disk drives and different density formats, CP/M's file allocation system could lead to inefficient disk space usage. The smallest allocatable unit increased from 1 KB on single-density drives to 2 KB or more on double-density drives, meaning even a single-byte file could occupy a much larger block of disk space.

What were some examples of CP/M derivatives or compatible operating systems?

Examples include IMDOS for the IMSAI 8080, Cromemco CDOS, MSX-DOS for MSX computers, TPM-II/III on Epson QX-10, Pro-DOS for the SAM Coupé, and various Eastern Bloc derivatives like SCP and CP/J. TurboDOS was a notable enhancement that supported multi-processor systems.

How did CP/M influence later operating systems like MS-DOS and Windows?

CP/M's influence is seen in MS-DOS and Windows through conventions like drive letters (A:, B:, C:), the 8.3 filename format, wildcard characters (*, ?), and reserved filenames (like CON:, PRN:). The Control-Z end-of-file marker also carried over.

What was the role of the BIOS in CP/M?

The BIOS (Basic Input/Output System) was the lowest-level component of CP/M, directly controlling hardware. It contained functions for character input/output to the console and reading/writing disk sectors, abstracting hardware variations from the rest of the OS.

What was the purpose of the CCP in CP/M?

The Console Command Processor (CCP) served as the user interface for CP/M. It accepted commands typed by the user, executed internal commands directly, or loaded and ran external (transient) programs.

How did CP/M handle disk sector sizes?

CP/M's BDOS initially assumed a fixed disk sector size of 128 bytes, common for single-density 8-inch floppy disks. For formats with larger sectors, the blocking and deblocking of data, along with buffer management, was handled by the model-specific code within the BIOS.

What was the 'software bus' concept in CP/M?

The 'software bus' concept referred to CP/M's ability to provide a standardized interface between applications and diverse hardware. This abstraction layer allowed software to run on different machines with minimal modification, primarily by adapting the BIOS.

What was the significance of Digital Research's open-source release of CP/M code?

In 1997 and 1998, Caldera released some CP/M 2.2 binaries and source code under an open-source license. This allowed for modification and redistribution, and later, Lineo expanded this license, making the code more accessible for preservation and development.

What was the 'resident monitor' aspect implied by CP/M's original name?

The original name 'Control Program/Monitor' implied a primitive, always-present program that managed basic system operations, similar to early resident monitors. This was a foundational concept that evolved into the more complex operating system.

How did CP/M's licensing strategy evolve?

CP/M started with very low licensing fees for early adopters, like Gnat Computers in 1977. However, as its market value became apparent, Digital Research significantly increased licensing costs, reflecting its growing importance as a standard.

What was the impact of independent programmers and 'hackers' on CP/M's software ecosystem?

The availability of affordable microcomputers running CP/M allowed independent programmers and hobbyists to acquire them. They shared their software creations through user groups, which was a significant driver of software innovation for the platform.

What was the purpose of the 'MOVCPM' utility?

MOVCPM was a utility provided with CP/M distributions that allowed users to relocate the operating system's code to different memory areas. This was necessary when adding more RAM to a system, as it required adjusting jump and call instructions to the new memory locations.

How did CP/M handle device-specific configurations like printers?

CP/M applications often required installation to configure device-specific features, such as printer control codes (escape sequences). Users typically ran an installation program to select or edit these sequences for different printers or terminals, as the OS itself did not standardize this.

What was the primary reason for the fragmentation of 5.25-inch disk formats in the CP/M era?

The lack of a standardized 5.25-inch disk format was due to the diverse choices made by manufacturers regarding sector size, density, track count, and sector layout. This fragmentation complicated software distribution, as distributors often had to support numerous formats.

What was the role of the 'zero page' in CP/M?

The 'zero page' in CP/M refers to the memory addresses from 0 to 255 (0x00 to 0xFF). It contained critical system pointers and data structures, including the jump table for BDOS calls and the location of the BDOS itself, making it a vital part of the OS's internal workings.

How did CP/M's user areas differ from subdirectories found in later operating systems?

CP/M's user areas were a way to partition files on a disk into 16 distinct logical groups, identified by numbers (0-15). Unlike subdirectories, they did not create a hierarchical file structure but rather separated files into different numbered 'spaces' on the same disk.

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A Look Back: The History of CP/M

Birth of an OS

CP/M, originally "Control Program/Monitor" and later "Control Program for Microcomputers," emerged in 1974. Developed by Gary Kildall at Digital Research, it was designed for Intel 8080/85-based microcomputers. Its architecture, influenced by mainframe systems like DEC's TOPS-10, provided a structured environment for managing files and running applications.

Rise to Dominance

By the late 1970s and early 1980s, CP/M became the de facto standard operating system for the burgeoning microcomputer market, particularly for S-100 bus systems. Its key advantage was portability; software written for CP/M could run on various hardware configurations, fostering a rich ecosystem of applications and reducing development effort for manufacturers.

The IBM PC Shift

The landscape shifted dramatically with the introduction of the IBM PC in 1981. Despite Digital Research's efforts and a significant price difference compared to Microsoft's MS-DOS, CP/M-86 struggled to gain traction. This marked the beginning of CP/M's decline as MS-DOS rapidly became the dominant standard for the new generation of personal computers.

The Engine Room: Core Components

BIOS (Basic Input/Output System)

The BIOS served as the hardware abstraction layer. It contained low-level drivers responsible for interacting directly with the system's hardware, such as the console (keyboard/display) and disk drives. Each CP/M system required a customized BIOS to match its specific hardware configuration.

BDOS (Basic Disk Operating System)

BDOS formed the core of CP/M's file management and system services. It implemented the file system structure, handled file operations like opening, reading, and writing, and provided standardized interfaces for applications, abstracting away the complexities of the underlying BIOS.

CCP (Console Command Processor)

The CCP was the user's gateway to the operating system. It functioned as the command-line interpreter, accepting user commands, executing built-in utilities (like DIR, ERA), or loading and running external programs (transient commands).

Evolution: Key Versions

CP/M-80 (8-bit)

The foundational version, running on 8-bit processors like the Intel 8080 and Zilog Z80. It was limited to 64KB of RAM but became the industry standard for early microcomputers.

CP/M Plus (CP/M 3.0)

Released in 1983, this was the final major 8-bit iteration. It introduced enhancements like bank switching for expanded memory access (beyond 64KB), date stamping, and improved performance, making it suitable for the later generation of 8-bit machines.

CP/M-86 (16-bit)

Developed for the Intel 8086 processor, this version aimed to bring CP/M into the 16-bit era. However, its adoption was hampered by licensing issues with IBM and competition from MS-DOS.

CP/M-68K & CP/M-8000

These versions targeted different 16-bit architectures: CP/M-68K for the Motorola 68000 and CP/M-8000 for the Zilog Z8000. They required recompilation of software but extended CP/M's reach to new processor families.

The Software Ecosystem: Key Applications

Word Processing & Databases

Pioneering applications like WordStar (a dominant word processor) and dBase (an early relational database) were first developed for CP/M, showcasing its capabilities for business productivity.

Spreadsheets & Development

Productivity tools such as VisiCalc and SuperCalc, the precursors to modern spreadsheets, found a home on CP/M. Furthermore, a wide array of compilers and interpreters for languages like BASIC, FORTRAN, and Pascal fueled software development.

Games & Utilities

While graphics were limited, text-based adventures like Zork and Colossal Cave Adventure were popular. Essential utilities like XMODEM for reliable file transfers also emerged, demonstrating the platform's versatility.

Enduring Influence: CP/M's Legacy

Foundation for DOS

Many fundamental concepts of MS-DOS, and subsequently Windows, trace their roots back to CP/M. This includes the use of drive letters (A:, B:, C:), the 8.3 filename convention, wildcard characters (*, ?), and reserved device names (CON:, PRN:).

Design Principles

The CP/M architecture, particularly its modular design with the BIOS abstraction layer, influenced subsequent operating system designs. The concept of a standardized OS allowing software portability across different hardware was revolutionary for its time.

Retrocomputing Revival

Today, CP/M continues to be appreciated by enthusiasts in the retrocomputing community. Active development and support for CP/M-based platforms persist, keeping the legacy of this pioneering operating system alive.

Branching Out: Derivatives and Compatibles

Official & Compatible Systems

Beyond official versions like CP/M Plus and CP/M-86, numerous compatible operating systems emerged. These included Cromemco CDOS, MSX-DOS, and various systems developed in the Eastern Bloc (e.g., SCP, CP/A), many offering enhanced features or targeting specific hardware.

Enhancements and Replacements

Projects like ZCPR (Z80 Command Processor Replacement) provided enhanced command-line interfaces, while systems like TurboDOS offered multi-processor capabilities. These efforts extended the life and functionality of the CP/M paradigm.

Open Source Movement

In later years, Digital Research's assets, including CP/M source code, were made available under open-source licenses. This allowed for continued development, preservation, and experimentation by the retrocomputing community, ensuring CP/M's historical code remains accessible.

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CP/M: The Genesis of Microcomputer Operating Systems

💡 Dive in with Flashcard Learning! 💡

A Look Back: The History of CP/M ⏳

🚀 Birth of an OS

📈 Rise to Dominance

📉 The IBM PC Shift

The Engine Room: Core Components ⚙️

💾 BIOS (Basic Input/Output System)

🗄️ BDOS (Basic Disk Operating System)

⌨️ CCP (Console Command Processor)

Evolution: Key Versions 💻

3️⃣ CP/M-80 (8-bit)

➕ CP/M Plus (CP/M 3.0)

8️⃣6 CP/M-86 (16-bit)

6️⃣8 CP/M-68K & CP/M-8000

The Software Ecosystem: Key Applications ⌨️

✍️ Word Processing & Databases

📊 Spreadsheets & Development

🎮 Games & Utilities

Enduring Influence: CP/M's Legacy 🔗

➡️ Foundation for DOS

💡 Design Principles

🏛️ Retrocomputing Revival

Branching Out: Derivatives and Compatibles 🔄

🏢 Official & Compatible Systems

🛠️ Enhancements and Replacements

🌐 Open Source Movement

Teacher's Corner 🧑‍🏫

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References

📜 References

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Disclaimer ⚠️

📜 Important Notice

Dive in with Flashcard Learning!

A Look Back: The History of CP/M

Birth of an OS

Rise to Dominance

The IBM PC Shift

The Engine Room: Core Components

BIOS (Basic Input/Output System)

BDOS (Basic Disk Operating System)

CCP (Console Command Processor)

Evolution: Key Versions

CP/M-80 (8-bit)

CP/M Plus (CP/M 3.0)

CP/M-86 (16-bit)

CP/M-68K & CP/M-8000

The Software Ecosystem: Key Applications

Word Processing & Databases

Spreadsheets & Development

Games & Utilities

Enduring Influence: CP/M's Legacy

Foundation for DOS

Design Principles

Retrocomputing Revival

Branching Out: Derivatives and Compatibles

Official & Compatible Systems

Enhancements and Replacements

Open Source Movement

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice