INT 21,23 - Get File Size Using FCB

AH = 23h

DS:DX = pointer to an unopened ~FCB~

on return:

AL = 00 if successful

= FF if file not found

- determines the number of records in a file

- FCB must be setup with drive id, complete filename and

extension plus record length before call

- updates random record position in FCB located at DS:DX

with file record count