ZX Spectrum 16k
The cut-down version of the original Spectrum. Has no memory after $7fff, so all memory is contended. Not simulated by the Next since the 48k version is identical but has more memory.
ZX Spectrum 48k
The original Spectrum. Does not support memory remapping. 224 T-states per video line. 312 scanlines per frame. 64 preamble lines.
ZX Spectrum 128k
The first enhanced Spectrum made by Sinclair. Does support memory remapping and thus the shadow screen. 228 T-states per video line. 311 scanlines per frame. 63 preamble lines.
ZX Spectrum +2A / +3
The latest enhanced Spectrums after Amstrad rebranding.
Russian-made homebrew Spectrum. Eliminated contended memory and doubled the clock speed. 224 T-states per video line. 320 lines. 16 preamble lines.
Previous FPGA-based Spectrum enhancement. Added several new video modes and features.