diff --git a/README.MD b/README.MD
index 8f852cd..74bb71e 100644
--- a/README.MD
+++ b/README.MD
@@ -1,9 +1,9 @@
 EttinOS
 =======
 
-EttinOS is a minimalist 16-bit DOS-like hobbyist operating system for
-the IBM Personal Computer and compatible machines. Its git repository
-can be found at https://ahti.space/git/crazyettin/EttinOS and that of
+EttinOS is a minimalist 16-bit hobbyist disk operating system for the
+IBM Personal Computer and compatible machines. Its git repository can be
+found at https://ahti.space/git/crazyettin/EttinOS and that of
 EttinOS-extra, a collection of programs for the system, at
 https://ahti.space/git/crazyettin/EttinOS-extra.
 
@@ -39,13 +39,11 @@ The input system is inspired by typewriters. Typing a character
 overwrites the cursor location and the erase (=tab) key erases it. The
 space and backspace keys move the cursor.
 
-EttinOS assigns the drives letters from A to D and uses the FAT12 file
-system. The hidden and total sectors entries of the BIOS parameter
-block, the entire extended BIOS parameter block, file attributes, and
-the file access date are not supported and are ignored if present: as a
-result disk labels and subdirectories are not supported. Drive letters
-and file names are case-insensitive and the latter follow the 8.3
-format. Text files use CRLF line endings.
+EttinOS assigns the drives letters from A to D and uses a version of the
+MS-DOS 3.0 FAT12 file system (in actual use since 2.1) without support
+for file attributes and thus disk labels and subdirectories. Drive
+letters and file names are case-insensitive and the latter follow the
+8.3 format. Text files use CRLF line endings.
 
 Drives and files are specified as ([A-D]:) and ([A-D]:)FILENAME.EXT
 respectively. Specifying the current drive, indicated in the prompt, is
@@ -53,11 +51,11 @@ optional.
 
 A command can be followed by arguments separated from eachother and the
 command with spaces. Extra spaces are ignored. Commands other than
-changing the drive are stored as external programs: the command for a
-program is its file specification without the extension.
+changing the current drive are stored as external programs: the command
+for a program is its file specification without the extension.
 
 Commands included in EttinOS:
-  * [A-D]:: Change the drive.
+  * [A-D]:: Change the current drive.
   * ECHO:   Print a message. Syntax: ECHO Message to be printed
   * HELLO:  Print "Hello world!".
   * LIST:   Print a list of the files on a drive. Syntax: LIST DRIVE
@@ -80,7 +78,7 @@ has finished running.
 
 System calls:
   * Interrupt 0x20: Return to the shell.
-  * Interrupt 0x21: Input and output:
+  * Interrupt 0x21: String operations:
       * AH = 0x0: Print a string ending in a null from SI.
       * AH = 0x1: Read a string ending in a null of at most AL
                   characters to DI until a return.
@@ -88,8 +86,25 @@ System calls:
                   CRLF.
       * AH = 0x3: Read a string ending in a null of at most AL
                   characters to DI until a return and print a CRLF.
+      * AH = 0x4: (Under construction) Convert a decimal string ending
+                  in a null at SI to a value in AL.
+      * AH = 0x5: (Under construction) Convert a value in AL to a
+                  decimal string ending in a null at DI.
+      * AH = 0x6: (Under construction) Convert a hexadecimal string
+                  ending in a null at SI to a value in AL.
+      * AH = 0x7: (Under construction) Convert a value in AL to a
+                  hexadecimal string ending in a null at DI.
   * Interrupt 0x22: Disk operations:
-      * AH = 0x0: Load a file named at SI as a string ending in a null
+      * AH = 0x0: (Under construction) Load the directory of a drive
+                  named at SI as a string ending in a null to the offset
+                  BX and store the error codes in AL:
+                    * AL = 0x0: Succesful load
+                    * AL = 0x1: Drive not found
+                    * AL = 0x2: Unable to read disk
+      * AH = 0x1: (Under construction) Store a directory at the offset
+                  BX to a drive named at SI as a string ending in a
+                  null.
+      * AH = 0x2: Load a file named at SI as a string ending in a null
                   to the offset BX and store the file size in CX and the
                   error codes in AL:
                     * AL = 0x0: Succesful load
@@ -97,7 +112,7 @@ System calls:
                     * AL = 0x2: Unable to read disk
                     * AL = 0x4: File or command not found
                     * AL = 0x8: Not enough memory
-      * AH = 0x1: Save a file (under construction).
+      * AH = 0x3: (Under construction) Save a file.
 
 Known bugs
 ----------
diff --git a/src/BOOT.ASM b/src/BOOT.ASM
index 3b112e3..e6f8532 100644
--- a/src/BOOT.ASM
+++ b/src/BOOT.ASM
@@ -23,6 +23,7 @@ mediadescriptor db 0xf0
 sectorsperfat   dw 0x9
 sectorspertrack dw 0x12
 heads           dw 0x2
+hiddensectors   dw 0x0
 
 %else
 
@@ -37,10 +38,10 @@ mediadescriptor db 0xfd
 sectorsperfat   dw 0x2
 sectorspertrack dw 0x9
 heads           dw 0x2
+hiddensectors   dw 0x0
 
 %endif
 
-
 ;Setup
 ;Set the segments
 start:
diff --git a/src/LOADF.INC b/src/LOADF.INC
index 83aabe0..b7af675 100644
--- a/src/LOADF.INC
+++ b/src/LOADF.INC
@@ -16,8 +16,8 @@ push di
 
 ;Store the current drive and offset
 mov word [.pointer], bx
-mov dl, byte [drive]
-mov byte [.drive], dl
+mov dl, byte [curdrive]
+mov byte [drive], dl
 
 ;Change the drive if needed
 ;Check for a drive specification
@@ -53,7 +53,7 @@ mov cx, 0x0
 jmp .done
 ;Change the drive
 .contchdrive:
-mov [.drive], dl
+mov [drive], dl
 ;Move to the file name
 add si, 0x2
 
@@ -112,7 +112,7 @@ pop ax
 
 ;Load the disk description table
 ;Set the source
-mov dl, [.drive]
+mov dl, [drive]
 mov ch, 0x0
 mov dh, 0x0
 mov cl, 0x1
@@ -136,48 +136,48 @@ jmp .done
 ;Store the disk values used for the rest of the call
 .storevalues:
 mov ax, [buffer + 0xb]
-mov [.sectorsize], ax
+mov [sectorsize], ax
 mov al, [buffer + 0xd]
-mov [.clustersize], al
+mov [clustersize], al
 mov ax, [buffer + 0xe]
-mov [.reservedsectors], ax
+mov [reservedsectors], ax
 mov al, [buffer + 0x10]
-mov [.fats], al
+mov [fats], al
 mov ax, [buffer + 0x11]
-mov [.rootentries], ax
+mov [rootentries], ax
 mov ax, [buffer + 0x16]
-mov [.sectorsperfat], ax
+mov [sectorsperfat], ax
 mov ax, [buffer + 0x18]
-mov [.sectorspertrack], ax
+mov [sectorspertrack], ax
 mov ax, [buffer + 0x1a]
-mov [.heads], ax
+mov [heads], ax
 
 ;Calculate and store variables not found in the BPB
 ;Start of the root
 mov ah, 0x0
-mov al, [.fats]
-mul word [.sectorsperfat]
-add ax, [.reservedsectors]
-mov [.rootstart], ax
+mov al, [fats]
+mul word [sectorsperfat]
+add ax, [reservedsectors]
+mov [rootstart], ax
 ;Size of the root in sectors
-mov ax, [.rootentries]
+mov ax, [rootentries]
 mov dx, 0x20
 mul dx
 mov dx, 0x0
-div word [.sectorsize]
-mov [.rootsectors], ax
+div word [sectorsize]
+mov [rootsectors], ax
 ;Start of data
-add ax, [.rootstart]
-mov [.datastart], ax
+add ax, [rootstart]
+mov [datastart], ax
 
 ;Load the root
 ;Set the source
-mov ax, [.rootstart]
+mov ax, [rootstart]
 ;Set the destination
 mov si, buffer
 mov bx, si
 ;Set the size
-mov cx, [.rootsectors]
+mov cx, [rootsectors]
 ;Store the source and the loop counter in the stack
 .loadrootsector:
 push ax
@@ -194,7 +194,7 @@ pop cx
 pop ax
 ;Set the next sector
 add ax, 0x1
-add bx, word [.sectorsize]
+add bx, word [sectorsize]
 ;Load the next sector
 loop .loadrootsector
 
@@ -202,7 +202,7 @@ loop .loadrootsector
 ;Set DI to the root
 mov di, buffer
 ;Set the number of root entries
-mov cx, word [.rootentries]
+mov cx, word [rootentries]
 ;Set the entry pointer
 mov ax, 0x0
 ;Store the loop counter in the stack
@@ -238,8 +238,8 @@ cmp word [di + 0x13], 0x0
 jne .sizerror
 ;Get the cluster size in bytes
 mov ah, 0x0
-mov al, [.clustersize]
-mul word [.sectorsize]
+mov al, [clustersize]
+mul word [sectorsize]
 mov bx, ax
 ;Store the file size
 mov ax, [di + 0x11]
@@ -267,12 +267,12 @@ jmp .done
 mov ax, [di + 0xf]
 mov [.cluster], ax
 ;Set the source
-mov ax, [.reservedsectors]
+mov ax, [reservedsectors]
 call .calcsource
 ;Set the destination
 mov bx, buffer
 ;Set the size
-mov ax, [.sectorsperfat]
+mov ax, [sectorsperfat]
 ;Load the FAT
 mov ah, 0x2
 int 0x13
@@ -282,13 +282,13 @@ int 0x13
 ;Set the source
 mov ax, word [.cluster]
 sub ax, 0x2
-mul byte [.clustersize]
-add ax, [.datastart]
+mul byte [clustersize]
+add ax, [datastart]
 ;Set the destination
 mov bx, word [.pointer]
 ;Set the size
 mov ch, 0x0
-mov cl, byte [.clustersize]
+mov cl, byte [clustersize]
 ;Store the loop counter in the stack
 .loadsector:
 push cx
@@ -303,7 +303,7 @@ int 0x13
 pop ax
 ;Set the next sector
 add ax, 0x1
-add bx, word [.sectorsize]
+add bx, word [sectorsize]
 ;Load the loop counter from the stack
 pop cx
 ;Load the next sector
@@ -335,8 +335,8 @@ jge .success
 ;Store the address of the next cluster
 mov word [.cluster], ax
 ;Set the destination of the next cluster
-mov ax, [.sectorsize]
-mul word [.clustersize]
+mov ax, [sectorsize]
+mul word [clustersize]
 add word [.pointer], ax
 ;Load the next cluster
 jmp .loadcluster
@@ -362,18 +362,6 @@ mov ah, 0x0
 iret
 
 ;Data
-.drive           db 0x0
-.sectorsize      dw 0x0 ;bytes
-.clustersize     db 0x0 ;sectors
-.reservedsectors dw 0x0
-.fats            db 0x0
-.rootentries     dw 0x0
-.sectorsperfat   dw 0x0
-.sectorspertrack dw 0x0
-.heads           dw 0x0
-.rootstart       dw 0x0
-.rootsectors     dw 0x0
-.datastart       dw 0x0
 .file            times 0xb db 0x20
 .size            dw 0x0
 .cluster         dw 0x0
@@ -454,21 +442,21 @@ push bx
 mov bx, ax
 ;Calculate the sector
 mov dx, 0x0
-div word [.sectorspertrack]
+div word [sectorspertrack]
 add dl, 0x1
 mov cl, dl
 ;Load the logical sector from BX
 mov ax, bx
 ;Calculate the head and cylinder
 mov dx, 0x0
-div word [.sectorspertrack]
+div word [sectorspertrack]
 mov dx, 0x0
-div word [.heads]
+div word [heads]
 mov dh, dl ;Head
 mov ch, al ;Cylinder
 
 ;Load the drive number
-mov dl, byte [.drive]
+mov dl, byte [drive]
 
 ;Load BX and AX from the stack
 pop bx
diff --git a/src/PRINT.ASM b/src/PRINT.ASM
index 7e571b2..11586da 100644
--- a/src/PRINT.ASM
+++ b/src/PRINT.ASM
@@ -40,7 +40,7 @@ stosb
 ;Load
 load:
 mov bx, stack + 0x100
-mov ah, 0x0
+mov ah, 0x2
 int 0x22
 ;Check for errors
 cmp al, 0x0
diff --git a/src/SYSTEM.ASM b/src/SYSTEM.ASM
index 22079c1..b5e52b0 100644
--- a/src/SYSTEM.ASM
+++ b/src/SYSTEM.ASM
@@ -21,7 +21,7 @@ je readln
 iret
 ;Disk operations
 int0x22:
-cmp ah, 0x0
+cmp ah, 0x2
 je loadf
 ;To do: savef
 iret
@@ -50,9 +50,10 @@ mov [0x82], ax
 mov [0x86], ax
 mov [0x8a], ax
 
-;Store the boot drive number and set the drive letter
-mov [drive], dl
-call setdriveletter
+;Store the boot drive number as the current drive and set the current
+;drive letter
+mov [curdrive], dl
+call setcurdriveletter
 
 ;Print a welcome message
 mov si, welcomemsg
@@ -67,8 +68,8 @@ mov sp, 0x0
 sti
 
 ;Prompt for and read a command
-;Print the drive letter
-mov si, driveletter
+;Print the current drive letter
+mov si, curdriveletter
 mov ah, 0x0
 int 0x21
 ;Print a prompt
@@ -85,26 +86,24 @@ int 0x21
 cmp byte [input], 0x0
 jz shell
 
-;Check for a drive change command
+;Set SI at the command
 ;Set SI at input
 mov si, input
 ;Ignore leading spaces
 call ignoreleading
-;Check
+
+;Check for a current drive change command
 cmp byte [si + 0x1], ":"
 jne extract
 cmp byte [si + 0x2], 0x0
-je changedrive
+je changecurdrive
 cmp byte [si + 0x2], 0x20
-je changedrive
+je changecurdrive
 
 ;Extract the specification of the program file
 extract:
-;Set SI at input and DI at program
-mov si, input
+;Set DI at program
 mov di, program
-;Ignore leading spaces
-call ignoreleading
 ;Initialise program with spaces
 mov cx, 0xe
 mov al, 0x20
@@ -142,21 +141,28 @@ rep movsb
 ;Load the program
 mov bx, 0x3000
 mov si, program
-mov ah, 0x0
+mov ah, 0x2
 int 0x22
 ;Check for errors
 cmp al, 0x0
 jne shell
-;Pass the drive and command tail to the program
-mov dl, [drive]
+;Pass the current drive and command tail to the program
+mov dl, [curdrive]
 pop si
 call ignoreleading
 ;Execute the program
 jmp 0x3000
 
-;Change the drive
+;Print a command error message and return to the shell
+cmderror:
+mov si, cmderrormsg
+mov ah, 0x2
+int 0x21
+jmp shell
+
+;Change the current drive
 ;Get the BIOS equipment list
-changedrive:
+changecurdrive:
 int 0x11
 ;Get the number of floppy drives
 times 0x6 shr ax, 0x1
@@ -184,33 +190,44 @@ int 0x21
 jmp shell
 ;Change the drive
 contchdrive:
-mov [drive], dl
-call setdriveletter
+mov [curdrive], dl
+call setcurdriveletter
 jmp shell
 
-;Print a command error message and return to the shell
-cmderror:
-mov si, cmderrormsg
-mov ah, 0x2
-int 0x21
-jmp shell
+;Welcome message
+welcomemsg db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
 
-;Data
-welcomemsg   db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
-drive        db 0x0
-driveletter  db "?:", 0x0
+;Drive stuff
+curdrive     db 0x0
 driveletters db "AaBbCcDd"
-prompt       db "> ", 0x0
-input        times 0x4c db 0x0
-program      times 0xf db 0x0
-extension    db ".BIN", 0x0
-cmderrormsg  db "File or command not found", 0x0
-driverrormsg db "Drive not found", 0x0
+
+;Shell
+curdriveletter db "?:", 0x0
+prompt         db "> ", 0x0
+input          times 0x4c db 0x0
+program        times 0xf db 0x0
+extension      db ".BIN", 0x0
+cmderrormsg    db "File or command not found", 0x0
+driverrormsg   db "Drive not found", 0x0
+
+;Disk parameters
+drive           db 0x0
+sectorsize      dw 0x0 ;bytes
+clustersize     db 0x0 ;sectors
+reservedsectors dw 0x0
+fats            db 0x0
+rootentries     dw 0x0
+sectorsperfat   dw 0x0
+sectorspertrack dw 0x0
+heads           dw 0x0
+rootstart       dw 0x0
+rootsectors     dw 0x0
+datastart       dw 0x0
 
 ;***
 
 ;Set the drive letter
-setdriveletter:
+setcurdriveletter:
 
 ;Set the drive number and letter counters
 mov dh, 0x0
@@ -227,7 +244,7 @@ jmp .checkdrive
 ;Set the drive letter
 .set:
 mov al, [si]
-mov byte [driveletter], al
+mov byte [curdriveletter], al
 
 ;Return
 ret