diff --git a/metropolis/pkg/fat32/dos83.go b/metropolis/pkg/fat32/dos83.go
new file mode 100644
index 0000000..4956468
--- /dev/null
+++ b/metropolis/pkg/fat32/dos83.go
@@ -0,0 +1,93 @@
+package fat32
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"regexp"
+	"strings"
+)
+
+// By default, DOS names would be encoded as what Microsoft calls the OEM
+// code page. This is however dependant on the code page settings of the
+// OS reading the file name as it's not mentioned in FAT32 metadata.
+// To get maximum compatibility and make it easy to read in hex editors
+// this only encodes ASCII characters and not any specific code page.
+// This can still result in garbled data when using a non-latin code page,
+// but this is unavoidable.
+// This is legal as there is no specific requirements for generating these
+// DOS names and any semi-modern system should use the unicode filenames
+// anyways.
+
+var invalidDOSNameChar = regexp.MustCompile("^[^A-Z0-9!#$%&'()@^_\x60{}~-]$")
+
+// validDOSName matches names which are valid and unique DOS 8.3 file names as
+// well as valid ASCII
+var validDOSName = regexp.MustCompile(`^^([A-Z0-9!#$%&'()@^_\x60{}~-]{0,8})(\.[A-Z0-9!#$%&'()-@^_\x60{}~-]{1,3})?$`)
+
+func makeUniqueDOSNames(inodes []*Inode) error {
+	taken := make(map[[11]byte]bool)
+	var lossyNameInodes []*Inode
+	// Make two passes to ensure that names can always be passed through even
+	// if they would conflict with a generated name.
+	for _, i := range inodes {
+		for j := range i.dosName {
+			i.dosName[j] = ' '
+		}
+		nameUpper := strings.ToUpper(i.Name)
+		dosParts := validDOSName.FindStringSubmatch(nameUpper)
+		if dosParts != nil {
+			// Name is pass-through
+			copy(i.dosName[:8], []byte(dosParts[1]))
+			if len(dosParts[2]) > 0 {
+				// Skip the dot, it is implicit
+				copy(i.dosName[8:], []byte(dosParts[2][1:]))
+			}
+			if taken[i.dosName] {
+				// Mapping is unique, complain about the actual file name, not
+				// the 8.3 one
+				return fmt.Errorf("name %q occurs more than once in the same directory", i.Name)
+			}
+			taken[i.dosName] = true
+			continue
+		}
+		lossyNameInodes = append(lossyNameInodes, i)
+	}
+	// Willfully ignore the recommended short name generation algorithm as it
+	// requires tons of bookkeeping and doesn't result in stable names so
+	// cannot be relied on anyway.
+	// A FAT32 directory is limited to 2^16 entries (in practice less than half
+	// of that because of long file name entries), so 4 hex characters
+	// guarantee uniqueness, regardless of the rest of name.
+	var nameIdx int
+	for _, i := range lossyNameInodes {
+		nameUpper := strings.ToUpper(i.Name)
+		dotParts := strings.Split(nameUpper, ".")
+		for j := range dotParts {
+			// Remove all invalid chars
+			dotParts[j] = invalidDOSNameChar.ReplaceAllString(dotParts[j], "")
+		}
+		var fileName string
+		lastDotPart := dotParts[len(dotParts)-1]
+		if len(dotParts) > 1 && len(dotParts[0]) > 0 && len(lastDotPart) > 0 {
+			// We have a valid 8.3 extension
+			copy(i.dosName[8:], lastDotPart)
+			fileName = strings.Join(dotParts[:len(dotParts)-1], "")
+		} else {
+			fileName = strings.Join(dotParts[:], "")
+		}
+		copy(i.dosName[:4], fileName)
+
+		for {
+			copy(i.dosName[4:], fmt.Sprintf("%04X", nameIdx))
+			nameIdx++
+			if nameIdx >= math.MaxUint16 {
+				return errors.New("invariant violated: unable to find unique name with 16 bit counter in 16 bit space")
+			}
+			if !taken[i.dosName] {
+				break
+			}
+		}
+	}
+	return nil
+}