The history of DOS (Disk Operating System) goes back to 1981 and the advent of the IBM PC. Microsoft was asked to make an operating system for IBM. This new operating system was known as PC DOS. DOS was made to be able to load other software programs designed on a standard operating system. MS DOS is similar to PC DOS except for the hidden files that work with the firmware of the PC to interpret the hardware and software drivers.

System File Sizes in Bytes

DOS TYPE AND VERSION	DATE	COMMAND.COM	IO.SYS or IBMBIO.COM	MSDOS.SYS or IBMDOS.COM
PC 1.0	8-4-81	3,231	1,920	6,400
MS 1.0	8-4-81	3,231	1,920	6,400
PC 1.1	5-7-82	4,959	1,920	6,400
PC 2.0	3-8-83	17,792	4,608	17,152
MS 2.0	3-8-83	17,792	4,608	17,152
PC 2.1	10-20-83	17,792	4,736	17,024
MS 2.11	11-17-83	15,957	6,836	17,176
PC 2.11	5-30-84	18,272	5,120	17,408
PC 3.0	8-14-84	22,042	8,964	27,920
MS 3.0	8-14-84	22,042	8,964	27,920
PC 3.1	3-7-85	23,210	9,564	27,760
MS 3.1	3-7-85	23,210	9,564	27,760
PC 3.2	12-30-85	23,791	16,369	28,477
MS 3.2	7-7-86	23,612	16,138	28,480
MS 3.21	5-1-87	23,948	18,501	28,480
PC 3.3	3-17-87	25,307	22,100	30,159
MS 3.3	7-24-87	25,276	22,357	30,128
MS 3.3a	2-2-88	25,308	22,398	30,128
MS 4.0	10-6-88	37,254	32,874	36,903
MS 4.01	11-30-88	37,396	33,173	37,180
PC 4.01	4-3-89	37,396	33,173	37,180
MS 4.01a	4-7-89	37,557	33,337	37,376
MS 5.0	4-9-91	33,430	37,394	47,845
PC 5.0	5-9-91	47,987	33,430	37,378
PC 5.001a	2-28-92	48,006	33,446	37,378
PC 5.02	9-1-92	47,990	33,718	37,362
MS 6.0	3-10-93	52,925	40,470	38,138
IBM 6.1	6-29-93	52,589	40,964	38,138
PC 6.1	9-30-93	52,797	40,964	38,138
MS 6.2R0	9-30-93	54,619	40,566	38,138
MS 6.22	5-31-94	54,645	40,774	38,138
PC 6.3	12-31-93	54,654	40,758	37,174

Note: Microsoft had no official version of MS DOS prior to DOS 3.2. Only OEM Original Equipment Manufacturer versions were sold with the PC by the computer manufacture. This guide is just for reference. There may be a slight variation in size of the files if you are using OEM, MS DOS.