{"id":14051,"date":"2026-05-18T03:00:00","date_gmt":"2026-05-18T07:00:00","guid":{"rendered":"https:\/\/www.both.org\/?p=14051"},"modified":"2026-04-15T14:08:25","modified_gmt":"2026-04-15T18:08:25","slug":"customize-your-freedos-with-fdconfig-sys","status":"publish","type":"post","link":"https:\/\/www.both.org\/?p=14051","title":{"rendered":"Customize your FreeDOS with FDCONFIG.SYS"},"content":{"rendered":"
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The main configuration file for FreeDOS is a file in the root directory called FDCONFIG.SYS<\/code>. This file contains a series of lines, each setting a value such as LASTDRIVE=Z<\/code> or FILES=40<\/code>. For example, the default FDCONFIG.SYS<\/code> in FreeDOS 1.4 looks like this:<\/p>\n\n\n\n

SET DOSDIR=C:\\FreeDOS\n\n!COUNTRY=001,858,C:\\FreeDOS\\BIN\\COUNTRY.SYS\n!LASTDRIVE=Z\n!BUFFERS=20\n!FILES=40\n!MENUCOLOR=7,0\n\nMENUDEFAULT=2,5\nMENU 1 - Load FreeDOS with JEMMEX, no EMS (most UMBs), max RAM free\nMENU 2 - Load FreeDOS with JEMMEX (more compatible)\nMENU 3 - Load FreeDOS with JEMM386 (Expanded Memory)\nMENU 4 - Load FreeDOS low with some drivers (Safe Mode)\nMENU 5 - Load FreeDOS without drivers (Emergency Mode)\n\n123?DOS=HIGH\n123?DOS=UMB\n123?DOSDATA=UMB\n\n1?DEVICE=C:\\FreeDOS\\BIN\\JEMMEX.EXE NOEMS X=TEST I=TEST NOVME NOINVLPG\n2?DEVICE=C:\\FreeDOS\\BIN\\JEMMEX.EXE NOEMS X=TEST NOVME NOINVLPG\n34?DEVICE=C:\\FreeDOS\\BIN\\HIMEMX.EXE\n3?DEVICE=C:\\FreeDOS\\BIN\\JEMM386.EXE X=TEST NOVME NOINVLPG\n\nREM 123?DEVICEHIGH=C:\\FreeDOS\\BIN\\LOGGER.COM COLOR 256 XMS MONO 128 XMS\n\n12?SHELLHIGH=C:\\FreeDOS\\BIN\\COMMAND.COM C:\\FreeDOS\\BIN \/E:1024 \/P=C:\\FDAUTO.BAT\n345?SHELL=C:\\FreeDOS\\BIN\\COMMAND.COM C:\\FreeDOS\\BIN \/E:1024 \/P=C:\\FDAUTO.BAT<\/code><\/pre>\n\n\n\n
But what do all those lines mean? Why do some have a question mark (?<\/code>) or an exclamation point (!<\/code>), while other lines do not?<\/p>\n\n\n\n
A simple configuration<\/h2>\n\n\n\n
Let’s start with a simple configuration, so we can see what does what. Assume this very brief FDCONFIG.SYS<\/code> file:<\/p>\n\n\n\n
LASTDRIVE=Z\nBUFFERS=20\nFILES=40\nDEVICE=C:\\FDOS\\BIN\\HIMEMX.EXE\nSHELL=C:\\FDOS\\BIN\\COMMAND.COM C:\\FDOS\\BIN \/E:1024 \/P=C:\\FDAUTO.BAT<\/code><\/pre>\n\n\n\n
This configuration file contains only a few instructions:<\/p>\n\n\n\n
The first instruction tells FreeDOS how many drive letters to reserve in memory. (DOS uses letters to represent each drive attached to the system, and LASTDRIVE=Z<\/code> says to reserve drive letters from “A” to “Z.”). LASTDRIVE<\/code> affects the number of logical drives that your system can recognize. You probably don’t have any logical drives; the FreeDOS installer doesn’t set these up by default. In any case, it is safe to set LASTDRIVE=Z<\/code> on any FreeDOS system.<\/p>\n\n\n\n
The BUFFERS<\/code> line reserves memory for file buffers. A buffer helps to speed up certain processes that require storage, such as copying files. If you set a larger value for BUFFERS<\/code>, FreeDOS will reserve more memory\u2014and vice versa for smaller values. Most users will set this to BUFFERS=20<\/code> or BUFFERS=40<\/code>, depending on how often they need to read and write files on the system.<\/p>\n\n\n\n
The FILES<\/code> setting determines how many files DOS allows you to open at one time. If you run an application that needs to open many files at once, such as a Genealogy database, you may need to set FILES<\/code> to a larger value. For most users, FILES=40<\/code> is a reasonable value.<\/p>\n\n\n\n
DEVICE<\/code> is a special instruction that loads a device driver. DOS requires device drivers for certain hardware or configurations. The line in the example loads the HimemX device driver, so DOS can take advantage of expanded memory beyond the first 640 kilobytes.<\/p>\n\n\n\n
The last line tells the FreeDOS kernel where to find the command-line shell. By default, the kernel will look for the shell as COMMAND.COM<\/code>, but you can change it with the SHELL instruction. In this example, the shell is the COMMAND.COM<\/code> program, located in the \\FDOS\\BIN<\/code> directory on the “C:” drive.<\/p>\n\n\n\n
The other text at the end of the SHELL indicate the options to the COMMAND.COM<\/code> shell. The FreeDOS COMMAND.COM<\/code> supports several startup options to modify its behavior, including:<\/p>\n\n\n\n