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The main difference between those 2 systems Spectrum was among the Video Display methodfirst 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, some credit it as the machine which launched the UK IT industry. Licensing deals and clones followed, and earned Clive Sinclair a knighthood for "services to British industry".
The [[c64|Commodore 64]], BBC Microcomputer and later the [[CPC|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. 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.
The Spectrum is based on a [[Z80|Zilog Z80]]A Central processing unit running at 3.5MHz (or NEC D780C-1 clone). The original model Spectrum has 16KB (16*1024 bytes) of ROM and either 16KB or 48KB 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.
==Sinclair Research models==
[[File:ZXSpectrum48k.jpg|right|350px|thumb|ZX Spectrum 16K/48K (Dimensions (mm): 233*144*30 (W*H*D) @ ~552 grams)]]
[[File:ZX Spectrum+.jpg|thumb|ZX Spectrum+ (Dimensions (mm): 319?149?38 (W?H?D))]]
[[File:ZX Spectrum128K.jpg|thumb|ZX Spectrum 128]]
New features included 128KB RAM, three-channel audio via the AY-3-8912 chip, MIDI compatibility, an RS-232 serial port, an RGB monitor port, 32KB of ROM including an improved BASIC editor, and an external keypad. The machine was simultaneously presented for the first time and launched in September 1985 at the SIMO '85 trade show in Spain, with a price of 44,250 pesetas. Because of the large number of unsold Spectrum+ models, Sinclair decided not to start selling in the UK until January 1986 at a price of £179.95. No external keypad was available for the UK release, although the ROM routines to use it and the port itself, which was hastily renamed "AUX", remained. The Z80 processor used in the Spectrum has a 16-bit address bus, which means only 64KB of memory can be directly addressed. To facilitate the extra 80KB of RAM the designers used bank switching so that the new memory would be available as eight pages of 16KB at the top of the address space. The same technique was also used to page between the new 16KB editor ROM and the original 16KB BASIC ROM at the bottom of the address space. The new sound chip and MIDI out abilities were exposed to the BASIC programming language with the command ''PLAY'' and a new command ''SPECTRUM'' was added to switch the machine into 48K mode, keeping the current BASIC program intact (although there is no way to switch back to 128K mode). To enable BASIC programmers to access the additional memory, a RAM disk was created where files could be stored in the additional 80KB of RAM. The new commands took the place of two existing user-defined-character spaces causing compatibility problems with some BASIC programs. The Spanish version had the "128K" logo in white while the English one had the same logo in red. == Amstrad models == === ZX Spectrum +2 ===[[File:Zx spectrum graphicsZX Spectrum Plus2.jpeg|thumb|ZX Spectrum +2]]The '''ZX Spectrum +2''' was [[Amstrad]]'s first Spectrum, coming shortly after their [[Sinclair Research Ltd#Amstrad acquisition|purchase of the Spectrum range and "Sinclair" brand]] in 1986. The machine featured an all-spectrum plus2new grey case featuring a spring-loaded keyboard, dual joystick ports, and a built-in cassette recorder dubbed the "Datacorder" (like the [[Amstrad CPC 464]]), but was in most respects identical to the ZX Spectrum 128.jpgThe main menu screen lacked the Spectrum 128's "Tape Test" option, and the ROM was altered to account for a new 1986 Amstrad copyright message. These changes resulted in minor incompatibility problems with software that accessed ROM routines at certain addresses. Production costs had been reduced and the retail price dropped to £139–£149. The new keyboard did not include the BASIC keyword markings that were found on earlier Spectrums, except for the keywords ''LOAD'', ''CODE'' and ''RUN'' which were useful for loading software. This was not a major issue however, as the +2 boasted a menu system, almost identical to the ZX Spectrum 128, where one could switch between 48k BASIC programming with the keywords, and 128k BASIC programming in which all words (keywords and otherwise) must be typed out in full (although the keywords are still stored internally as one character each). Despite these changes, the layout remained identical to that of the 128. The ZX Spectrum +2 power supply was a grey version of the ZX Spectrum+ and 128 power supply. === ZX Spectrum +2A ===[[File:Spectrum 128-2.png|thumb|ZX Spectrum +2A]]The '''ZX Spectrum +2A''' was a variant of the Spectrum +3 housed a black version of the Spectrum +2 case mouldings. The Spectrum +2A/+3 motherboard (AMSTRAD part number Z70830) was designed such that it could be assembled without the [[floppy disk controller]] or associated logic and a +2 style "datacorder" connected. Originally, Amstrad planned to introduce an additional disk interface for the +2A/+2B called the '''AMSTRAD SI-1''', however this never appeared. If an external disk drive was added, the "+2A" on the system OS menu would change to a +3. The power supply of the ZX Spectrum +2A used the same [[pinout]] as the +3. However, the power supply purchased with the +2A/B had "Sinclair +2" written on the case. === ZX Spectrum +3 === [[File:ZX Spectrum Plus3.jpeg|thumb|ZX Spectrum +3]]The '''ZX Spectrum +3''' looked similar to the +2 but featured a built-in 3-inch [[floppy disk]] drive (like the Amstrad CPC 6128) instead of the tape drive, and was in a black case. It was launched in 1987, initially retailed for £249 and then later £199 and was the only Spectrum capable of running the [[CP/M]] operating system without additional hardware. The +3 saw the addition of two more 16 kB ROMs. One was home to the second part of the reorganised 128 ROM and the other hosted the +3's disk operating system. This was a modified version of Amstrad's [[PCWDOS]] (the disk access code used in [[LocoScript]]), called +3DOS. These two new 16 kB ROMs and the original two 16 kB ROMs were now physically implemented together as two 32 kB chips. To be able to run CP/M, which requires RAM at the bottom of the address space, the bank-switching was further improved, allowing the ROM to be paged out for another 16 kB of RAM. Such core changes brought incompatibilities: * Removal of several lines on the expansion bus edge connector (video, power, and IORQGE); caused many external devices problems; some such as the VTX5000 modem could be used via the "FixIt" device.* Dividing ROMCS into 2 lines, to disable both ROMs* Reading a non-existent I/O port no longer returned the last attribute; caused some games such as ''[[Arkanoid]]'' to be unplayable* Memory timing changes; some of the RAM banks were now contended causing high-speed colour-changing effects to fail* The keypad scanning routines from the ROM were removed* move 1 byte address in ROM Some older 48K and a few older 128K games were incompatible with the machine. The ZX Interface 1 was incompatible due to differences in ROM and expansion connector; therefore it was not possible to connect and use the Microdrive units. The ZX Spectrum +3 power supply provides the same voltages as the one supplied with +2A/B. This power supply has the same DIN connector so can also be used with the +2A/B. However, the power supply purchased with the +3 had "Sinclair +3" written on the case. Production of the +3 ceased in December 1990, believed to be in response for Amstrad relaunching their CPC range. At the time, it was estimated about 15% of ZX Spectrums sold had been +3 models. Production of the +2B (the only other model then still in production) continued, as it was believed not to be in competition with other computers in Amstrad's product range. === ZX Spectrum +2B and +3B === The ''ZX Spectrum +2B'' and ''ZX Spectrum +3B'' were functionally similar in design to the Spectrum +2A and +3. The main electronic differences being simply changes to the generation of the audio output signal to resolve problems with [[Clipping (audio)|clipping]] and the removal of the external tape loading input ("ear" pin). Unlike the +2A the Spectrum +2B motherboard (AMSTRAD part number Z70833) does not have provision for floppy disk controller circuitry so cannot be assembled as a +3B. The +3B motherboard is Amstrad part number Z70835. ==Notes== * From and Amstrad CPC user's point of view the ZX Spectrum is well known for being the source of [[Speccy Port|Speccy Ports]].* The Spectrum +2 case design is comparable to the CPC464's case design because of the internal datacorder. The Spectrum +3 design shares some similarities with the CPC6128, the case design is similar with it's internal 3" disc drive, and the disc controller is the same as the CPC6128's. The CPC464 and CPC6128 came before these Spectrum's, so it is clear Amstrad used those as inspirations to update the Spectrum design. === Links === * http://scratchpad.wikia.com/wiki/ZX_Spectrum_technical_information
[[Category: Non CPC Computers| ]][[Category:Amstrad Products|*]][[Category:CPC History]]