=== 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.<ref>''Spectrum +3 Service Manual''. AMSTRAD. p.18.</ref> Originally, Amstrad planned to introduce an additional disk interface for the +2A/+2B called the '''AMSTRAD SI-1''',<ref>Spital, Ivor. ''Sinclair ZX Spectrum +2A''. AMSTRAD, 1987. p.354.</ref> 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.<ref>{{cite web|url=http://hardware.speccy.org/hardware/Fuente+2A/imagenes/vista_superior.jpg|title=Image of Spectrum +2A power supply|accessdate=21 December 2012}}</ref>{{clear}}
=== 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<ref>{{Cite journal| last = South | first = Phil | year = 1987 | month = July | title = It's here... the Spectrum +3 | journal = [[Your Sinclair]] | issue = 17|pages = 22–23 | url = http://www.worldofspectrum.org/showmag.cgi?mag=YourSinclair/Issue19/Pages/YourSinclair1900022.jpg | accessdate =5 August 2008 }}</ref> and then later £199<ref>{{Cite journal| author = Amstrad | year = 1987 | month = November | title = The new Sinclair has one big disk advantage | journal = [[Sinclair User]] | issue = 68 | pages = 2–3 | url = http://www.worldofspectrum.org/showmag.cgi?mag=SinclairUser/Issue068/Pages/SinclairUser06800002.jpg | accessdate =5 August 2008 | authorlink = Amstrad }}</ref> 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.
* 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.<ref>{{Cite journal| last = Goodwin | first = Simon | year = 1987 | month = December | title = Tech Tips - +3 Faults | journal = [[Crash (magazine)|Crash]] | issue = 48 |pages = 145 | accessdate = 20 August 2012 }}</ref>
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.<ref>{{cite web|url=http://www.yorkdistribution.co.uk/acatalog/York_Distribution_Power_supply_for_Spectrum_128___2A___3_2337.html|title=Power supply for Spectrum 128, +2A, +3|publisher=York Distribution Limited|accessdate=21 December 2012}}</ref> 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.<ref>{{Cite journal| year = 1990 | month = December | title = Death of the +3 | journal = [[Your Sinclair]] | issue = 60|pages = 10–11 }}</ref> It was eventually discontinued in 1992.<ref name="bbc6572711"/>
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.<ref>''Spectrum +2B/+3B Service Manual''. AMSTRAD.</ref> 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.
* 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 case design is comparable to shares some similarities with the CPC6128's , the case design because of the 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 their knowledge and experience those as inspirations to alter update the Spectrum design in this way. === Links === * http://scratchpad.wikia.com/wiki/ZX_Spectrum_technical_information
[[Category: Non CPC Computers| ]][[Category:Amstrad Products|*]][[Category:CPC History]]