ZX-Spectrum

Pubblicato: giugno 24, 2011 in Sinclair
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From Wikipedia, the free encyclopedia

The ZX Spectrum (the “Z” is pronounced “Zed” from its original British English branding) is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd. Referred to during development as the ZX81 Colour and ZX82,[2][3] the machine was launched as the ZX Spectrum by Sinclair to highlight the machine’s colour display, compared with the black-and-white of its predecessor, the Sinclair ZX81.[4] The Spectrum was ultimately released as eight different models, ranging from the entry level model with 16 KB RAM released in 1982 to the ZX Spectrum +3 with 128 KB RAM and built in floppy disk drive in 1987; together they sold in excess of 5 million units worldwide.

The Spectrum was among the first mainstream audience home computers in the UK, similar in significance to the Commodore 64 in the USA. The introduction of the ZX Spectrum led to a boom in companies producing software and hardware for the machine,[6] the effects of which are still seen;[1] some credit it as the machine which launched the UK IT industry.[7] Licensing deals and clones followed, and earned Clive Sinclair a knighthood for “services to British industry”.[8]

The Commodore 64, BBC Microcomputer and later the Amstrad CPC range were major rivals to the Spectrum in the UK market during the early 1980s. The ZX Spectrum has enjoyed a resurgence in popularity thanks to the accessibility of ZX Spectrum emulators, allowing 1980s video game enthusiasts to enjoy classic titles without the long loading times associated with data cassettes and the issues with using an actual machine in areas that use NTSC. Over 20,000 titles have been released since the Spectrum’s launch and new titles continue to be released, with over 90 new ones in 2010.

Hardware

The Spectrum is based on a Zilog Z80A CPU running at 3.5 MHz (or NEC D780C-1 clone). The original model Spectrum has 16 KB (16×1024 bytes) of ROM and either 16 KB or 48 KB of RAM. Hardware design was by Richard Altwasser of Sinclair Research, and the machine’s outward appearance was designed by Sinclair’s industrial designer Rick Dickinson.[6]

Video output is through an RF modulator and was designed for use with contemporary portable television sets, for a simple colour graphic display. Text can be displayed using 32 columns × 24 rows of characters from the ZX Spectrum character set or from a set provided within an application, from a palette of 15 shades: seven colours at two levels of brightness each, plus black.[9] The image resolution is 256×192 with the same colour limitations.[10] To conserve memory, colour is stored separate from the pixel bitmap in a low resolution, 32×24 grid overlay, corresponding to the character cells. Altwasser received a patent for this design.[11]

An “attribute” consists of a foreground and a background colour, a brightness level (normal or bright) and a flashing “flag” which, when set, causes the two colours to swap at regular intervals.[10] Unfortunately, this scheme leads to what was dubbed colour clash or attribute clash with some bizarre effects in the animated graphics of arcade style games. This problem became a distinctive feature of the Spectrum and an in-joke among Spectrum users, as well as a point of derision by advocates of other systems. Other machines available around the same time, for example the Amstrad CPC, did not suffer from this limitation. The Commodore 64 used colour attributes in a similar way, but a special multicolour mode, hardware sprites and hardware scrolling were used to avoid attribute clash.

Sound output is through a beeper on the machine itself. This is capable of producing one channel with 10 octaves. The machine also includes an expansion bus edge connector and audio in/out ports for the connection of a cassette recorder for loading and saving programs and data.

Firmware

The machine’s Sinclair BASIC interpreter is stored in ROM (along with fundamental system-routines) and was written by Steve Vickers on contract from Nine Tiles Ltd. The Spectrum’s chiclet keyboard (on top of a membrane, similar to calculator keys) is marked with BASIC keywords, so that, for example, pressing “G” when in programming mode would insert the BASIC command GOTO.[12]

The BASIC was developed from that used on the ZX81 and a ZX81 BASIC program can be typed into a Spectrum largely unmodified, but Spectrum BASIC included many extra features making it easier to use. The ZX Spectrum character set was expanded from that of the ZX81, which did not feature lower-case letters. Spectrum BASIC included extra keywords for the more advanced display and sound, and also supported multi-statement lines. The cassette interface was also much more advanced, saving and loading around four times faster than the ZX81, and much more reliably. As well as being able to save programs, the Spectrum could in addition save the contents of arrays, the contents of the screen memory, and the contents of any defined range of memory addresses.

ZX Spectrum 16K/48K

The original ZX Spectrum is remembered for its rubber keyboard, diminutive size and distinctive rainbow motif. It was originally released in 1982 with 16 KB of RAM for £125 Sterling or with 48 KB for £175;[14] these prices were later reduced to £99 and £129 respectively.[15] Owners of the 16 KB model could purchase an internal 32 KB RAM upgrade, which for early “Issue 1” machines consisted of a daughterboard. Later issue machines required the fitting of 8 dynamic RAM chips and a few TTL chips. Users could mail their 16K Spectrums to Sinclair to be upgraded to 48 KB versions. To reduce the price, the 32 KB extension used eight faulty 64 kilobit chips with only one half of their capacity working and/or available. Links on the PCB were configured accordingly so as to place these faulty memory locations in the other (unused) half of each IC.[16] External 32 KB RAM packs that mounted in the rear expansion slot were also available from third parties. Both machines had 16 KB of onboard ROM.

About 60,000 “Issue 1” ZX Spectrums were manufactured; they can be distinguished from later models by the colour of the keys (light grey for Issue 1, blue-grey for later models).[17]

Peripherals

Several peripherals for the Spectrum were marketed by Sinclair: the ZX Printer was already on the market,[30] as the ZX Spectrum expansion bus was backwards-compatible with that of the ZX81.

The ZX Interface 1 add-on module included 8 kB of ROM, an RS-232 serial port, a proprietary LAN interface (called ZX Net), and an interface for the connection of up to eight ZX Microdrives – somewhat unreliable but speedy tape-loop cartridge storage devices released in July 1983.[31][32] These were later used in a revised version on the Sinclair QL, whose storage format was electrically compatible but logically incompatible with the Spectrum’s. Sinclair also released the ZX Interface 2 which added two joystick ports and a ROM cartridge port.[33]

There were also a plethora of third-party hardware addons. The better known of these included the Kempston joystick interface, the Morex Peripherals Centronics/RS-232 interface, the Currah Microspeech unit (speech synthesis),[34] Videoface Digitiser,[35] RAM pack, the Cheetah Marketing SpecDrum,[36] a drum machine, and the Multiface,[37] a snapshot and disassembly tool from Romantic Robot. Keyboards were especially popular in view of the original’s notorious “dead flesh” feel.[38]

There were numerous disk drive interfaces, including the Abbeydale Designers/Watford Electronics SPDOS, Abbeydale Designers/Kempston KDOS and Opus Discovery. The SPDOS and KDOS interfaces were the first to come bundled with Office productivity software (Tasword Word Processor, Masterfile database and OmniCalc spreadsheet). This bundle, together with OCP’s Stock Control, Finance and Payroll systems, introduced many small businesses to a streamlined, computerised operation. The most popular floppy disk systems (except in East Europe) were the DISCiPLE and +D systems released by Miles Gordon Technology in 1987 and 1988 respectively. Both systems had the ability to store memory images onto disk snapshots could later be used to restore the Spectrum to its exact previous state. They were also both compatible with the Microdrive command syntax, which made porting existing software much simpler.[39]

During the mid-1980s, Telemap Group Ltd launched a fee-based service allowing users to connect their ZX Spectrums via a Prism Micro Products VTX5000 modem to a viewdata service known as Micronet 800, hosted by Prestel. This service pre-dated the World Wide Web, but offered many of the services now considered commonplace.[citation needed]

Software

The Spectrum enjoys a vibrant, dedicated fan-base.[40][41] Since it was cheap and simple to learn to use and program, the Spectrum was the starting point for many programmers.[1] The hardware limitations of the Spectrum imposed a special level of creativity on game designers, and so many Spectrum games are very creative and playable even by today’s standards.[42] The early Spectrum models’ great success as a games platform came in spite of its lack of built-in joystick ports, primitive sound generation, and colour support that was optimised for text display.[43]

The Spectrum family enjoys a very large software library of more than 20,000 titles[44] which is still increasing. While most of these are games, the library is very diverse, including programming language implementations, databases (e.g. VU-File[45]), word processors (e.g. Tasword II[46]), spreadsheets (e.g. VU-Calc[45]), drawing and painting tools (e.g. OCP Art Studio[47]), and even 3D-modelling (e.g. VU-3D[48][49]) and archaeology software[50] amongst many other types.[51]

Distribution

Most Spectrum software was originally distributed on audio cassette tapes. The Spectrum was intended to work with a normal domestic cassette recorder,[52] and despite differences in audio reproduction fidelity, the software loading process was quite reliable, if somewhat slow (by today’s standards).

Although the ZX Microdrive was initially greeted with good reviews,[53] it never took off as a distribution method due to worries about the quality of the cartridges and piracy.[54] Hence the main use became to complement tape releases, usually utilities and niche products like the Tasword word processing software and Trans Express, (a tape to microdrive copying utility). No games are known to be exclusively released on Microdrive.

Despite the popularity of the DISCiPLE and +D systems, most software released for them took the form of utility software. The ZX Spectrum +3 enjoyed much more success when it came to commercial software releases on floppy disk. More than 700 titles were released on 3-inch disk from 1987 to 1997.[44]

Software was also distributed through print media; magazines[55] and books.[56] The reader would type the Sinclair BASIC program listing into the computer by hand, run it, and could save it to tape for later use. The software distributed in this way was in general simpler and slower than its assembly language counterparts. Magazines also printed long lists of checksummed hexadecimal digits with machine code games or tools.

Another software distribution method was to broadcast the audio stream from the cassette on another medium and have users record it onto an audio cassette themselves. In radio or television shows in many European countries, the host would describe a program, instruct the audience to connect a cassette tape recorder to the radio or TV and then broadcast the program over the airwaves in audio format.[57] Some magazines distributed 7″ 33⅓ rpm flexidisc records, a variant of regular vinyl records which could be played on a standard record player.[58] These disks were known as floppy ROMs.

Copying and backup software

Many copiers—utilities to copy programs from audio tape to another tape, microdrive tapes, and later on diskettes—were available for the Spectrum.[59] As a response to this, publishers introduced copy protection measures to their software, including different loading schemes.[60] Other methods for copy prevention were also used including asking for a particular word from the documentation included with the game—often a novella like in Silicon Dreams trilogy—or another physical device distributed with the software—e.g. Lenslok as used in Elite. Special hardware, such as Romantic Robot’s Multiface, was able to dump a copy of the ZX Spectrum RAM to disk/tape at the press of a button, entirely circumventing the copy protection systems.

Most Spectrum software has, in recent years, been converted to current media and is available for download. One popular program for converting Spectrum files from tape is Taper; it allows connecting a cassette tape player to the line in port of a sound card, or—through a simple home-built device—to the parallel port of a PC.[61] Once in files on a host machine, the software can be executed on one of many emulators, on virtually any platform available today.

The largest on-line archive of ZX Spectrum software is World of Spectrum, with more than 21,000 titles. The legality of this practice is still in question and while a number of copyright holders have explicitly objected to the posting of their software, others have given their permission for their games to be archived as part of the preservation project.[62]

Notable developers

A number of current leading games developers and development companies began their careers on the ZX Spectrum, including David Perry of Shiny Entertainment, and Tim and Chris Stamper (founders of Ultimate Play The Game, now known as Rare, maker of many famous titles for Nintendo and Microsoft game consoles). Other prominent games developers include Julian Gollop (Chaos, Rebelstar, X-COM series), Matthew Smith (Manic Miner, Jet Set Willy), Jon Ritman (Match Day, Head Over Heels), The Oliver Twins (the Dizzy series), Clive Townsend (Saboteur), Pete Cooke (Tau Ceti), Mike Singleton (The Lords of Midnight,War In Middle Earth), and Alan Cox.[63] Although the Spectrum’s audio hardware was not as capable as chips in other popular 8-bit home computers of the era, computer musicians David Whittaker and Tim Follin produced notable multi-channel music for the machine.

Jeff Minter ported some of his Commodore VIC-20 games for the ZX Spectrum.[64]

Community

The ZX Spectrum enjoyed a very strong community early on. Several dedicated magazines were released including Sinclair User (1982), Your Sinclair (1983) and CRASH (1984). Early on they were very technically oriented with type-in programs and machine code tutorials. Later on they became almost completely game-oriented. Several general contemporary computer magazines covered the ZX Spectrum in more or less detail. They included Computer Gamer, Computer and Video Games, Computing Today, Popular Computing Weekly, Your Computer and The Games Machine.[65]

The Spectrum is affectionately known as the Speccy by elements of its fan following.[66]

More than 80 electronic magazines existed, many in Russian. Most notable of them were AlchNews (UK), ZX-Format (Russia), and Spectrofon (Russia).

It is a welll known fact that many of the present game programmers actually got a grounding in programming through the ZX Spectrum. (A case in point are the programmers of the game Startopia who actually included a cheat code in the game which allowed the user to play the game in the same 8 bit format as used in the Spectrum.)

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