Retrocomputing
Retrocomputing is the use of older computer hardware and software in modern times. Retrocomputing is usually classed as a hobby and recreation rather than a practical application of technology; enthusiasts often collect rare and valuable hardware and software for sentimental reasons. However, some do make use of it.

Historical retrocomputing
A more serious line of retrocomputing is part of the history of computer hardware. It can be seen as the analogue of experimental archaeology in computing. Some notable examples include the reconstruction of Babbage's Difference engine (more than a century after its design) and the implementation of Plankalkül in 2000 (more than half a century since its inception).

"Homebrew" computers

Some retrocomputing enthusiasts also consider the "homebrewing" (designing and building of retro- and retro-styled computers or kits), to be an important aspect of the hobby, giving new enthusiasts an opportunity to experience more fully what the early years of hobby computing were like.  There are several different approaches to this end. Some are exact replicas of older systems, and some are newer designs based on the principles of retrocomputing, while others combine the two, with old and new features in the same package. Examples include:
 Device offered by IMSAI, a modern, updated, yet backward-compatible version and replica of the original IMSAI 8080, one of the most popular early personal systems;
 Several Apple 1 replicas and kits have been sold in limited quantities in recent years, by different builders, such as the "Replica 1", from Briel Computers;
 A currently ongoing project that uses old technology in a new design is the Z80-based N8VEM;
 The Arduino Retro Computer kit is an open source, open hardware kit you can build and has a BASIC interpreter. There is also a version of the Arduino Retro Computer that can be hooked up to a TV;
 There is at least one remake of the Commodore 64 using an FPGA configured to emulate the 6502;
 MSX 2/2+ compatible do-it-yourself kit GR8BIT, designed for the hands-on education in electronics, deliberately employing old and new concepts and devices (high-capacity SRAMs, micro-controllers and FPGA);
 The MEGA65 will be a Commodore 65 compatible computer;
 The Commander X16 is an ongoing project that hopes to build a new 8-bit platform inspired by the Commodore 64, using off the shelf modern parts.
The C256 Foenix and its different versions is a new retro computer family based on the WDC65C816. FPGAs are used to simulate CBM custom chips and has the power of an Amiga with its graphic and sound capabilities.

Vintage computers
The personal computer has been around since approximately 1971. But in that time, numerous technological revolutions have left generations of obsolete computing equipment on the junk heap. Nevertheless, in that time, these otherwise useless computers have spawned a sub-culture of vintage computer collectors, who often spend large sums to acquire the rarest of these items, not only to display but restore to their fully functioning glory, including active software development and adaptation to modern uses. This often includes so-called hackers who add-on, update and create hybrid composites from new and old computers for uses for which they were otherwise never intended.  Ethernet interfaces have been designed for many vintage 8-bit machines to allow limited connectivity to the Internet; where users can access user groups, bulletin boards and databases of software.  Most of this hobby centers on those computers manufactured after 1960, though some collectors specialize in pre-1960 computers as well.

MITS Inc.
Micro Instrumentation and Telemetry Systems (MITS) produced the Altair 8800 in 1975, which is widely regarded as starting the microcomputer revolution.

IMSAI
IMSAI produced a machine similar to the Altair 8800, though considered by many  to be a more robust design.

Processor Technology
Processor Technology produced the Sol-20.  This was one of the first machines to have a case that included a keyboard; a design feature copied by many of later "home computers".

SWTPC
Southwest Technical Products Corporation (SWTPC) produced the SWTPC 6800 and later the SWTPC 6809 kits that employed the Motorola 68xx series microprocessors.  The 68xx line was to be followed later by the 6502 processor that was used in many early "home computers", such as the Apple II.

Apple Inc.
The earliest of the Apple Inc. personal computers are among some of the most collectable. They are relatively easy to maintain in an operational state thanks to Apple's use of readily available off-the-shelf parts.

Apple I: The Apple-1 was Apple's first product and has brought some of the highest prices ever paid for a microcomputer at auction.
Apple II: The Apple II series of computers are some of the easiest to adapt, thanks to the original expansion architecture designed into them. New peripheral cards are still being designed by an avid thriving community, thanks to the longevity of this platform, manufactured from 1977 through 1993. Numerous websites exist to support not only the legacy users, but new adopters who weren't even born when the Apple II was discontinued by Apple.
Macintosh: Perhaps because of its friendly design and first commercially successful graphical user interface as well as its enduring Finder application that persists on the most current Macs, the Macintosh is one of the most collected and used of the vintage computers. With dozens of websites around the world, old Macintosh hardware and software is put into daily use. Many maintain vast collections of functional and non-functional systems, which are lovingly maintained and discussed on worldwide user forums. The Macintosh had a strong presence in many early computer labs, creating a strong nostalgia factor for former students who recall their first computing experiences.

RCA
 The COSMAC ELF in 1976 was an inexpensive (about $100) single-board computer that was easily built by hobbyists. Many people who could not afford an Altair could afford an ELF, which was based on the RCA 1802 chip. Because the chips are still available from other sources, modern recreations of the ELF are fairly common and there are a number of fan web sites.

IBM
 The IBM 1130 computing system from 1966 which still has a following of interested users, albeit via an emulator rather than the actual machine.
 The 5100 also has an avid collector and fan base.
 The PC series (5150 PC, 5155 Portable PC, 5160 PC/XT, 5170 PC/AT) has become very popular in recent years, with the earliest models (PC) being considered the most collectible.

Acorn BBC & Archimedes
 The Acorn BBC Micro was a very popular British computer in the 1980s with home and educational users, and enjoyed near universal usage in British schools into the mid-1990s.  It was possible to use 100K -inch disks, and it had many expansion ports.
 The Archimedes series the de facto successor to the BBC Micro has also enjoyed a following in recent years, thanks to its status as the first computer to be based around ARM's RISC microprocessor.

Tandy/Radio Shack
 The Tandy/RadioShack Model 100 is still widely collected and used as one of the earliest examples of a truly portable computer.  Other Tandy offerings, such as the TRS-80 line, are also very popular, and early systems, like the Model I, in good condition can command premium prices on the vintage computer market.

Sinclair
 The Sinclair ZX81 and ZX Spectrum series were the most popular British home computers of the early 1980s, with a wide choice of emulators available for both platforms.  The Spectrum in particular enjoys a cult following due to its popularity as a games platform, with new games titles still being developed even today.  Original "rubber key" Spectrums fetch the highest prices on the second hand market, with the later Amstrad-built models attracting less of a following.  The earlier ZX81 is not as popular in original hardware form due to its monochrome display and limited abilities next to the Spectrum, but still unassembled ZX81 kits still appear on EBay occasionally.

MSX
 Although nearly nonexistent in the United States, the MSX architecture has strong communities of fans and hobbyists worldwide, particularly in Japan (where the standard was conceived and developed), South Korea (the only country had a MSX based game console, Zemmix), Netherlands, Spain, Brazil, Argentina, Russia, Chile, the Middle East and others. New hardware and software are being actively developed to this day as well.
 One of the latest fundamental (from hardware and software perspectives) revivals of the MSX is the GR8BIT.

Robotron
 The Robotron Z1013 was an East German home computer produced by VEB Robotron. It had a U880 processor, 16 kByte RAM and a membrane keyboard.
 The KC 85 series of computers was a modular 8 bit computer system used in East German schools.

Commodore

 The Commodore 64 was the most sold singular model of computer in the world.
 The Commodore PET was the first computer made by commodore, and is highly collectible.
 The VIC-20 is the friendly computer and the first computer for Elon Musk and Linus Torvalds (creator of Linux).

Xerox

 The Xerox Alto, designed and manufactured by Xerox PARC and released in 1973, was the first personal computer equipped with a graphic user interface.  In 1979, Steve Jobs of Apple Inc. arranged for his engineers to visit Xerox in order to see the Alto.  The design concepts of the Alto soon appeared in the Apple Lisa and Macintosh systems.
 The Xerox Star, also known as the 8010/40, was made available in 1981.  It followed on the Alto.  Like the Alto, this machine was expensive and was only intended for corporate office usage.  Therefore, being out of the price range of the average user, this product had little market penetration.

Silicon Graphics

 The SGI Indy, built in 1993 for Silicon Graphics has a history of usage in the development of the Nintendo 64 as well as various CGI projects throughout the 1990s and early 2000s. The Indy and other machines in the SGI lineup have remained cult classics

In popular culture
In an interview with Conan O'Brien in May 2014, George R. R. Martin revealed that he writes his books using WordStar 4.0, an MS-DOS application dating back to 1987.
US-based streaming video provider Netflix recently released a multiple-choice movie branded to be part of their Black Mirror series, called Bandersnatch. The protagonist is a teenage programmer working on a contract to deliver a video-game adaptation of a fantasy novel for an 8-bit computer in 1984. The multiple storylines evolve around the emotions and mental health issues resulting from a reality-perception mismatch between a new generation of computer-savvy teenagers and twenty-somethings, and their care givers.

Education
Due to their low complexity together with other technical advantages, 8-bit computers are frequently re-discovered for education, especially for introductory programming classes in elementary schools. 8-bit computers turn on and directly present a programming environment; there are no distractions, and no need for other features or additional connectivity. The BASIC language is a simple-to-learn programming language that has access to the entire system without having to load libraries for sound, graphics, math, etc. The focus of the programming language is on efficiency; in particular, one command does one thing immediately (i.e., COLOR 0,6 turns the screen green).

Reception
Retrocomputing (and retrogaming as aspect) has been described in one paper as preservation activity and as aspect of the remix culture.

Internet
Though many retro computers pre-date widespread use of the Internet many enthusiasts find way to connect their machines using technologies such as Retronet that emulate the modems and X.25 protocol the machines were designed at the time to use.

See also
 Computer Conservation Society
 Computer History Museum
 History of computing hardware
 List of home computers by video hardware
 Living Computers: Museum + Labs
 Retrogaming
 SIMH, the multi-system emulator
 Vintage Computer Festival

References

"Preserving Computing's Past: Restoration and Simulation" Max Burnet and Bob Supnik, Digital Technical Journal, Volume 8, Number 3, 1996.

External links
Retro Computer Museum, a computer museum in Leicestershire, UK with regular "come and play" open days
Retrocomputing Museum for re-implementations of old programming languages
RETRO German paper mag about digital culture
The Centre for Computing History The Centre for Computing History UK Computer Museum
Living Computer Museum Request a Login from the LCM to interact with vintage computers over the internet.
bitsavers Software and PDF Document archive about older computers
Vintage Computing Resources Active resources for retrocomputing hobbyists
Learning to code in a “retro” programming environment
Beginning Programming Using Retro Computing
LOAD ZX Spectrum Museum, a retro computing museum in Portugal mostly focused on the Sinclair line of computers

 
History of computing
Nostalgia