The Sinclair ZX Spectrum was one of the most popular European computers of the 80's. Two models were launched: one with 16 kb RAM and one with 48 kb RAM.
One of its most "interesting" characteristics is its keyboard! Some keys have more than five (!) functions! It is impossible to type BASIC keywords letter by letter, instead you have to use function keys. A lot of peripherals and programs were developed for this computer. It seems that several models of this computers were launched (at least 3), but I've no technical details about them. It was replaced in 1984 by the Spectrum + and in 1985 by the Spectrum 128.
Alan Wilson reports to us :
The 16K version of the computer had only the 16K ram chips loaded, while the 48K version had both banks full.
To keep the prices down Sinclair used faulty 64K chips (internally 2 X 32K). All the chips in the 32K bank of RAM had to have the same half of the 64K chips working. A link was fitted on the pcb in order to choose the first half or the second half.
It was possible with a few logic chips for the experimenter to have access to the faulty 32K bank.