Answer:
Following are the external commands of DOS:
Append, Arp, Assign, At, Attrib, Backup, Cacls, Chcp, Chkdsk, Chkntfs, Choice, Cipher, Comp, Compact, Convert, Debug, Defrag, Delpart, Deltree, Diskcomp, Diskcopy, Doskey, Dosshell, Dumpchk, Edit, Edlin, Expand, Extract, Fasthelp, Fc, Fdisk, Find, Format, FTP, Gpupdate, Graftabl, Help, Hostname, Ipconfig, Label, Loadfix, logoff, Mem, Mode, More, Msav, Msbackup, Mscdex, Mscdexnt, Mwbackup, Msd, Nbtstat, Net, Netsh, Netstat, Nlsfunc, Nslookup, Pathping, Ping, Power, Print, Reg, Route, Runas, Scandisk, Scanreg, Setver, Sfc, Share, Shutdown, Smartdrv, Sort, Subst, Sys, Systeminfo, Taskkill, Telnet, Tracert, Tree, Undelete, Unformat and Xcopy.