NCR PC4i Owner's Manual

Also see for PC4I: Technical reference Service manual Service manual

Contents

NCR PC4i Owner's Manual Manual pdf 20 page image

HISTORICAL DATAprograms are read from external storage into internal memory at thestart of the day or the start of the specific run under CPU control.Data files are read from external memory into internal memory asneeded. In fact, unless a data file is relatively small, only the portionof the file currently being accessed is read into internal memory.Portions of files are read either sequentially or randomly, dependingon the characteristics of the external memory hardware and thedesign of the application program.Also, data are input into internal memory from an input keyboard orother device if required by the program.When processing of the data in internal memory is complete, thendata modified, added, or created are written out to external memory.Information to be printed or displayed to the operator on the CRT isalso transferred from internal memory, under CPU control.When the current program is finished, the next set of applicationprograms and data to be processed replaces the information in theinternal memory.Information in RAM memory is recorded electronically, but is“volatile”. That is, its content is maintained by a constant smallelectric current; the information is lost if the current is interrupted.ROM memory, by contrast, is permanent; the information stored isnot affected if the power to the computer is turned off. Informationstored in ROM when it is manufactured cannot be changed.One almost universal use of ROM memory is to contain a routine toset up (“boot”) the machine for processing whenever the power isturned on. This routine normally loads the operating system softwarefrom external memory and then passes control to the operatingsystem.Another use of ROM in some small business and personal computersis to contain BASIC language interpreter routines.External MemoryExternal memory includes all forms of data storage other thaninternal memory. Most external memory devices magnetically recordinformation on and read information from some form of magneticdisks or tapes. Other types of external memory (used much less inrecent years) are nonmagnetic, such as punched cards or punchedpaper tape.External memory devices which record and read magnetically are oftwo primary types:1-12 OWNER S MANUAL