'Early' 5150 (One with 16KB-64KB Motherboard)




The 16KB-64KB version of the 5150 motherboard is fitted with a maximum of 64 KB of RAM.
Therefore, with no RAM cards added, at best, the 5150 has a total of 64 KB of RAM.

64 KB is not enough RAM for later versions of DOS.  For example, as shown at here, IBM DOS 3.3 will report "Configuration too large for memory" (even with no CONFIG.SYS/AUTOEXEC.BAT).

128 KB is enough for booting purposes.
Of course, depending on what you'll be doing after boot, you may require additional RAM.