via the Electron's expansion connector. For Issue 1–4 motherboards, the ULA had an issue similar to those experienced by other socketed CPUs. Over time, the thermal heating and cooling could cause the ULA to rise slightly out of its socket just enough to cause the machine to start exhibiting 'hanging' or other startup-failure issues, such as a continuous 'startup beep'. This was despite a metal cover, and locking-bar mechanism designed to prevent this from occurring. Pushing down on the metal cover to reseat the ULA was normally sufficient to rectify these issues. Issue 5 and 6 boards utilized a different ULA type, this being known as the Aberdeen ULA (as opposed to the earlier Ferranti ULA) which was mounted on a board that was directly soldered to the main board, with the chip being covered by epoxy resin "insulating material". This arrangement dispensed with the 68-pin socket, and this new type of ULA was expected to be "less prone to failure". This type of ULA was also used on the German release of the Electron mainboard which is designated by the marking "GERMAN ELECTRON Issue 1" on the mainboard rather than just "ELECTRON" as for the UK model. The keyboard includes a form of quick keyword input, similar to that used on the Sinclair ZX Spectrum, through use of the key in combination with other keys labelled with BASIC keywords. However, unlike the Spectrum, this method of rapid keyword entry is optional, and keywords can be entered manually if preferred. The ULA mediates access to 32 KB of addressable RAM using 4 64-kilobit RAM chips (4164), sharing the RAM between the CPU and the video signal generation (or screen refresh) performed by the ULA itself. Two accesses have to be made to the RAM to get each byte (albeit with a single RAS), delivering a maximum transfer rate to or from RAM of one byte per 2 MHz cycle. In generating the video signal, the ULA is able to take advantage of this 2 MHz bandwidth when producing the picture for the high-bandwidth screen modes. Due to signalling constraints, the CPU can only access RAM at 1 MHz, even when it is not competing with the video system. When the ULA is consuming all of the RAM bandwidth during the active portion of a display line, the CPU is unable to access the RAM. (The Electron uses the Synertek variant