 Inside the case , there were many more similarities with the ZX81 . Like its successor , it used the <unk> microprocessor and had only 1 KB of on @-@ board RAM . It came with a specially written BASIC interpreter on a dedicated ROM chip and could use a television as a display . It relied on an ordinary cassette tape recorder for data storage . The main difference between the two machines lay in the internal software ; when the ZX81 was released , ZX80 owners were able to upgrade by the relatively simple expedient of plugging a new ROM onto the circuit board . 
