Inside the infamous ZX Spectrum, you can find a board that was upgraded and improved over the years. From top to bottom, you can see:

• The first model (Issue 1), characterized by having its tracks drawn by hand, a trait that gave these board their unique beauty. This model has a 16KB memory since, for this board, any memory extension was done by using an additional board (a daughter board), as you can see on Spectrum no. 829.
• After this board, the Issue 2 followed. It is during this time that keyboards colours change from light grey to the blue-ish tone that had been introduced and that became more common.
• Along with Issue 3, the heat sink (the aluminium plate) changed position and is visible when looking to the Spectrum’s extension area.
• This models if followed by Issue 3B, Issue 4A and Issue 4B.
• Up until very recently it was thought that Issue 5 never even existed, but you can observe one of them in this photograph from Will Woodvine. We only known about the existence of two models of this Issue, belonging to collectors we know of, one of them being Woodvine.
• Last but not least, there is Issue 6A, which is fairly known.