The computer architecture should emphasise the memory rather than the 
central processing unit. This is appropriate for control applications and moni- 
toring external equipment. Logic- and control circuits can be hardwired (e.g. 
by methalised paths) or stored programme systems can be employed instead. 
The latter permit programme modifications even after a system is installed. 
The length of output data should be ten digits or more. A sensible set of 
service programmes should be provided. 
Table-top calculators (e.g. Hewlett Packard, Wang) meet the require- 
ments for most of the functions in serial systems (5). The main shortcoming 
concerns programming which is difficult due to small storage capacity. Newer 
tabletop calculators employ microprocessors. Some permit programming in a 
higher level language, though most of them are programmable in a machine 
language only. The former is easier for users, whereas the latter is more 
efficient. Storages for programmes and data are sometimes common and 
sometimes separate. Most of the table-top calculators permit a limited 
extension of storage. They are equipped with a visual display unit and a key- 
board. Their capacity to monitor peripheral units is restricted. The common 
peripheral units are: typewriter, fast printer, magnetic cassette, magnetic 
plate unit, Floppy Disk, a small flat-bed or drum plotter, and A/D converters. 
The merits of table-top calculators are: availability of several display registers, 
simple maintenance, low price and convenient operation. Some typical short- 
comings are: small storage capacity, limited possibility for extension, limited 
choice of peripheral units, and restricted compatibility. 
Minicomputers are more powerful than table-top calculators with 
regard to storage, data processing, and ability to monitor different peripheral 
units. Basic- and application software should be supplied to users together 
with the computer. An operational system should include a set of service 
programmes, i.e. for loading, debugging, compiling, processing text, etc. 
Separate storages for programmes and for fast changing data might be 
preferable. Internal storage is expandable and additional external storages 
and other peripheral units can be connected. 
Microcomputers are less expensive and more compact than minicom- 
puters. However, they normally use shorter word length (i.e. 4 to 16 bits), 
which increases the number of steps per operation. This and inherently 
slower performance of the MOS (Metal Oxide Semi-conductor) devices,