Computerised Systems Transactions are recorded on computer. A computer is not an information system. There are a number of methods of inputting data using computers. The processor performs arithmetical calculations. Electronic storage is usually fixed inside the machine.
Magnetic storage consists of magnetic tape and disks.
Magnetic storage can be written to and read from many times. Optical storage consists of CD-ROM and DVD disks. CD-ROM disks have a capacity of 700Mb approximately. Most optical storage can only be written to once. Optical storage is the cheapest of all 3 methods.