*Spectrum was released in the UK in 1982. The Amstrad was released in the UK in 1984.
*Spectrum 48K sold for £99. The CPC464 with Green Screen monitor sold for £299 and with colour monitor for £399. One selling point was that the Amstrad needed only 1 plug, and that you didn't need to use the family television to use it. Also the Spectrum 48k wasn't supplied with any Monitor nor Mass Data Storage device.
*Spectrum (48K machine) has 48K RAM, approx 6.5k of this is screen. The Amstrad has 64K ram, approx 16K of this is screen.
*Spectrum and Amstrad both have a bitmapped display.
*They have a similar screen size. But Amstrad CPC actually produce smaller pixels in "equivalent" Video Mode, as for the approximately same area the normal display resolution on the Amstrad CPC is 320x200 (mode 1) while ZX Spectrum produces "only" 256x192 pixels. Amstrad's screen can be reduced in size to match the Spectrum's (256x192, in Mode1). Normal but then the actual display size on Amstrad wondow is 320x200 (mode 1)quite smaller as on a spectrum, with a large Border because the pixels have a constant size.
*Spectrum (128K model and later) and Amstrad both have an AY-3-8912 sound chip. (1.7Mhz clock for AY in spectrum, 1.0Mhz clock for AY in Amstrad).
*Spectrum 48K had a 1-bit beeper sound. Playing sounds through the beeper is very CPU intensive. The Amstrad doesn't have a beeper. The only way to simulate the beeper sound would be to convert it to AY sound.
*The size and aspect of the pixels in the Spectrum's bitmapped display are comparable to the pixels in Amstrad's mode 1 bitmapped displayin that both produce approximately square pixels.
*The Spectrum's video ram takes approx 6K. The Amstrad's video ram takes 16K (approx 12K when screen is reduced).