ZX Spectrum 48K motherboard (Issue 3B — 1983, heat sink removed)
The Spectrum is based on a
Zilog Z80 A
CPU running at 3.5
D780C-1 clone). The original model has 16 KB (16×1024
ROM and either 16 KB or 48 KB of
RAM. Hardware design was by
Richard Altwasser of Sinclair Research, and the outward appearance was designed by Sinclair's industrial designer
Video output is through an
RF modulator and was designed for use with contemporary
portable television sets, for a simple colour graphic display. Text can be displayed using 32 columns × 24 rows of characters from the
ZX Spectrum character set or from a set provided within an application, from a palette of 15 shades: seven colours at two levels of brightness each, plus black.
image resolution is 256×192 with the same colour limitations.
 To conserve memory, colour is stored separate from the pixel
bitmap in a low resolution, 32×24 grid overlay, corresponding to the character cells. In practice, this means that all pixels of an 8x8 character block share one
foreground colour and one
background colour. Altwasser received a
patent for this design.
An "attribute" consists of a foreground and a background colour, a brightness level (normal or bright) and a flashing "flag" which, when set, causes the two colours to swap at regular intervals.
 This scheme leads to what was dubbed colour clash or
attribute clash, where a desired colour of a specific pixel could not necessarily be selected. This became a distinctive feature of the Spectrum, meaning programs, particularly games, had to be designed around this limitation. Other machines available around the same time, for example the
Amstrad CPC or the
Commodore 64, did not suffer from this limitation. The Commodore 64 used colour attributes in a similar way, but a special
multicolour mode, hardware
hardware scrolling were used to avoid
Sound output is through a beeper on the machine itself, capable of producing one channel with 10 octaves.
Software was later available that could play two channel sound. The machine includes an
edge connector and 3.5 mm audio in/out ports for the connection of a
cassette recorder for loading and saving programs and data. The "ear" port can drive headphones and the "mic" port provides
 audio out which could be amplified.