DIALOG:
 Person A) What are the different modes of operation of the IBM Personal Computer?;
 Person B) Because BASIC was over 50 kB in size, this served a useful function during the first three years of the PC when machines only had 64–128 kB of memory, but became less important by 1985.;
 Person A) what are the different modes of operation?;
 Person B) For comparison, clone makers such as Compaq were forced to include a version of BASIC that resided entirely in RAM.;
 Person A) Are there any other interesting aspects about this article?;
 Person B) The first IBM 5150 PCs had two 5.25-inch 160 KiB single sided double density (SSDD) floppy disk drives.;
 Person A) did they have any other models?;
 Person B) As two heads drives became available in the spring of 1982, later IBM PC and compatible computers could read 320 KiB double sided double density (DSDD) disks with software support of MS-DOS 1.25 and higher.;
 Person A) what are the different modes of operation for each model?;
 Person B) 

The same type of physical diskette media could be used for both drives but a disk formatted for double-sided use could not be read on a single-sided drive.