zx80
	The machine the ZX81 was based on
	sold ready assembled or as a set
	approx. 14 standard ICs
	4k ROM
	1k RAM
	
zx81
	The machine the Spectrum was based on
	8k ROM
	1k RAM

zx spectrum 16k pre-production/early issue 1	(•)
	some had the 'cockroach' patch
	grey rubber keys
	16k rom
	16k ram, contended

zx spectrum 16k issue 1/issue 2
	some issue 2 machines had all chips on sockets
+	blue rubber keys
	16k rom
	16k ram, contended

zx spectrum 48k issue 1/issue 2					(•)
	blue rubber keys
	16k rom
	16k ram, contended
+	32k ram

zx spectrum 48k issue 3							(•)
	blue rubber keys
	16k rom
	16k ram, contended
	32k ram
+	ula_ear_in (bit 6) is low if ula_ear_out low and ula_mic_out high

zx spectrum+ issue 4
+	black keyboard
	16k rom
	16k ram, contended
	32k ram
	ula_ear_in behaves as in issue 3

zx spectrum +128								(•)
	black keyboard
+	16k rom (basic)					(very similar to 48k rom)
+	16k rom (editor)
+	64k ram, contended
+	64k ram 
	ula_ear_in behaves as in issue 3
+	AY sound chip, mono
+	different timings (cpu clock, cycles/row, rows above screen)

zx spectrum +2									(•)
+	grey keyboard
+	built-in tape recorder
+	16k rom (basic)					(new copyright message)
+	16k rom (editor)				(no test tape menu item)
	64k ram, contended
	64k ram 
	ula_ear_in behaves as in issue 3
	AY sound chip, mono
	timings as in +128
	
zx spectrum +3									(•)
+	black keyboard
+	built-in disk drive
+	16k rom (basic)					(modified)
+	16k rom (editor)				(modified)
+	32k rom (+3dos, ext. basic)
	64k ram, contended
	64k ram 
+	ram pageable to $0000
	AY sound chip, mono
+	ula_ear_in (bit 6) always 0 if no tape signal present
+	reading from n.ex. port always returns $FF
+	different timing (contendion)
	- waitmap 1-1-1-1-1-1-1-0
	- wait linked with mreq => less wait positions in machine cycles

zx spectrum +3B 
	supposedly fixes some bugs in the ROM, but almost inevitably generates 
	some as well. The syntax ROM is different to the one in the +3, this 
	creates some problems with amongst others Tasword +3, Slowdos, DiSCDOS

zx spectrum +2A
	black keyboard
+	built-in tape recorder
	16k rom (basic)					??identical to +3??
	16k rom (editor)				??identical to +3??
+	32k rom (+3dos, ext. basic)		(later versions)
	64k ram, contended
	64k ram 
	ram pageable to $0000
	AY sound chip, mono
	ula_ear_in behaves as in +3
	reading from n.ex. port as in +3
	timing as in +3
	race condition in boot code: booting succeeds only if reset starts at cc = 0..2000  or  7000..14000
	
zx spectrum +2B  (and late +2A)
	probably identical to zx +2A except of printed/embossed label
+	32k rom (+3dos, ext. basic)		(version 4.1)


// ----- clones, non-Sinclair/Amstrad, localised versions -----

Timex TC 2048
	based on zx spectrum 48k
	Timex, Portugal 
	original ROM + one out instr in boot code to set screen mode
	incl. kempston port
	ULA port $FE is fully decoded
	slightly clocked faster
	better keyboard
	4 screen modes incl. 512*192 screen mode ??? (SAM Coupé also has this screen mode)   
	port 0xF4 is probably screen modes and memory map                                            

Timex TS 2068									(•)
	based on zx spectrum 48k
	Timex, USA
	modified ROM +8K shadow ROM
	better keyboard 
	AY sound chip (different port address than zx spectrum 128)
	512*192 screen mode (SAM Coupé also has this screen mode)                                               
	port 0xF4 is probably screen modes and memory map                                            

inves spectrum+									(rom)
	based on zx spectrum 48k
	Investronica, Spain
	May have had an AY chip
	Localised ROM
	no contended ram (no waitstates)
	xtal 17734500 Hz, probably 17734500/5 = 3546900 Hz cpu clock
	70908 cc / frame  =  311 lines x 57 x 4 cc  

zx spectrum 128									(rom)
	Investronica, Spain     
	This was the original 128
    Came with the keypad (although only the Spanish 128 came with the keypad 
    it is supported by every subsequent machine, from the UK 128 right up to last +2B)
    Localised error messages

TK90X											(?)
	based on zx spectrum 48k
	Microdigital, Brazil
	own unique ROM

TK95											(?)
	based on zx spectrum 48k
	Microdigital, Brazil
	improved TK90X ROM

PENTAGON										(?)
	based on zx spectrum 128
	hobbyists, USSR
	same Basic ROM as 128
	Boot ROM includes option to use TR-DOS (Betadisk)
	includes TR-DOS ROM
	different timing
	no contended RAM
	http://www.void.demon.nl/rusfaq/index.html

SCORPION										(•)
	based on zx spectrum 128
	hobbyists, USSR
	similar to Pentagon 
	64k ROM including a monitor program
	256k RAM 
	processor is Z80B, has a high speed mode

Spanish +2										(rom)
	localised error messages

Spanish +3										(rom)
	localised error messages

French +2										(rom)
	localised 'Press PLAY & REC' message

Sam Coupé										(•)
	the natural successor of the zx spectrum
	4 screen modes, 1x specci, 2 same resolution, 1x 512x192
	CPU 6MHz
	32k ROM
	256k RAM