The PDP-8 was a popular 12-bit minicomputer manufactured by DEC in the 1960s and 1970s, used for business, industrial, and scientific applications. It lacked pre-installed operating system software and used paper and magnetic tape for storage. Different models were produced, with new instructions, registers, and I/O devices. The PDP-8 was replaced by cheaper microcomputers in the late 1970s. Today, enthusiasts have implemented the PDP-8 in a single FPGA chip and software emulators, and vintage computers can still be found.
A PDP-8 was a 12-bit minicomputer manufactured by Digital Equipment Corporation (DEC) from the mid-1960s through the late 1970s. It included a simple processor, main memory, and at least one input/output (I/O) device, such as a teleprinter. These computers were often used for business applications as well as for controlling industrial machines and scientific experiments.
Unlike many modern computers, the PDP-8 did not include pre-installed operating system software. A simple program can be typed using the switches on the front panel of the machine. Typically this was a boot loader, which then carried other software from a data storage device; paper tape and magnetic tape were the most common PDP storage media at the time. Compilers and interpreters were available for a variety of computer programming languages, including BASIC, DIBOL, FOCAL, and FORTRAN. Several operating systems have also been developed for this machine; OS/8 was one of the most commonly used.
Many different models of PDP-8s were produced. For example, the PDP-8/E introduced an advanced memory controller to support virtual machines. The /A model increased core memory capacity beyond the 32K word limit. Other models often added instructions and registers. Over time, new types of I/O devices have also been introduced, including disk drives, cartridge tape drives, and analog-to-digital converters.
Early PDP-8 systems were built with individual transistors, diodes, and resistors. In the late 1960s, TTL integrated circuits replaced many of these components, simplifying manufacturing. In a final move to save power and simplify the design, custom CMOS integrated circuits were used in the late 1970s.
The PDP-8 was very popular in the early 1970s; it was the first powerful computer that could be purchased cheaply rather than rented. Many companies used them to manage their business operations, including accounting and inventory control. Some were even rented out to the public by the hour in computer centers; programming, word processing, and playing games were common activities. PDP stands for Programmable Data Processor; DEC generally avoided using the term computer, often associated with a large and expensive array of machines. By the late 1970s, smaller, lower-priced microcomputers from Apple and Tandy were taking away much of its market.
The PDP-8 processor, memory and control circuitry are not very complex by today’s standards; enthusiasts have implemented all of this in a single FPGA chip, making cheap hardware “clones” a reality. There are several software emulators that can run PDP programs. Much of the original DEC system documentation is also available on the Internet. One website even offers online access to a real working PDP-8 system. Many of these vintage computers still work; some continue their original functions, while others can be purchased from auction sites and private collectors.
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