diff --git a/README.MD b/README.MD
index 8bcda12..8f852cd 100644
--- a/README.MD
+++ b/README.MD
@@ -3,7 +3,9 @@ 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.
+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.
 
 System requirements
 -------------------
@@ -38,11 +40,12 @@ 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 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.
+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.
 
 Drives and files are specified as ([A-D]:) and ([A-D]:)FILENAME.EXT
 respectively. Specifying the current drive, indicated in the prompt, is
@@ -61,8 +64,8 @@ Commands included in EttinOS:
   * PRINT:  Print a text file. Syntax: PRINT FILE
 
 Both LIST and PRINT page their output if all of it does not fit on the
-screen at the same time. Press any key to continue printing after each
-screen.
+screen at the same time. Press any key other than escape to continue
+printing after each screen or escape to quit the program.
 
 Programming
 -----------
diff --git a/src/BOOT.ASM b/src/BOOT.ASM
index d134d08..3b112e3 100644
--- a/src/BOOT.ASM
+++ b/src/BOOT.ASM
@@ -1,122 +1,135 @@
-CPU 8086
-ORG 0x7c00
+cpu 8086
+org 0x7c00
 
+;Jump to the code
 jmp start
+
+;Padding
 nop
 
-;Disk description tables
+;OEM label
+db "ETTINOS "
 
 %ifdef F1440
-;1.44 MB 3.5" floppy disk (enable with the argument -d F1440)
-oemlabel        db "ETTINOS "
+
+;1.44 MB 3.5" floppy disk BPB (enable with the argument -d F1440)
 sectorsize      dw 0x200 ;bytes
 clustersize     db 0x1 ;sectors
-bootsectors     dw 0x1
+reservedsectors dw 0x1
 fats            db 0x2
 rootentries     dw 0xe0
 logicalsectors  dw 0xb40
 mediadescriptor db 0xf0
 sectorsperfat   dw 0x9
 sectorspertrack dw 0x12
-sides           dw 0x2
-hiddensectors   dd 0x0
-largesectors    dd 0x0
+heads           dw 0x2
 
 %else
-;360 KiB 5.25" floppy disk (default)
-oemlabel        db "ETTINOS "
+
+;360 KiB 5.25" floppy disk BPB (default)
 sectorsize      dw 0x200 ;bytes
 clustersize     db 0x2 ;sectors
-bootsectors     dw 0x1
+reservedsectors dw 0x1
 fats            db 0x2
 rootentries     dw 0x70
 logicalsectors  dw 0x2d0
 mediadescriptor db 0xfd
 sectorsperfat   dw 0x2
 sectorspertrack dw 0x9
-sides           dw 0x2
-hiddensectors   dd 0x0
-largesectors    dd 0x0
+heads           dw 0x2
 
 %endif
 
-start:
 
 ;Setup
-;Set up the data, stack, and extra segments
+;Set the segments
+start:
 mov ax, 0x0
 mov ds, ax
 mov ss, ax
 mov es, ax
-;Set up the stack
+;Set the stack
 cli
 mov sp, 0x0
 sti
 ;Store the boot drive number
 mov [drive], dl
 
-;Load the root
-;Set the source
+;Calculate and store variables not found in the BPB
+;Start of the root
 mov ah, 0x0
 mov al, [fats]
 mul word [sectorsperfat]
-add ax, [bootsectors]
-push ax
-;Set the destination
-mov si, buffer
-mov bx, si
-;Set the size
+add ax, [reservedsectors]
+mov [rootstart], ax
+;Size of the root in sectors
 mov ax, [rootentries]
 mov dx, 0x20
 mul dx
 mov dx, 0x0
 div word [sectorsize]
-mov cx, ax
-pop ax
+mov [rootsectors], ax
+;Start of data
+add ax, [rootstart]
+mov [datastart], ax
+
+;Load the root
+;Set the source
+mov ax, [rootstart]
+;Set the destination
+mov si, buffer
+mov bx, si
+;Set the size
+mov cx, [rootsectors]
+;Store the source and the loop counter in the stack
+loadrootsector:
 push ax
 push cx
-loadroot:
-push cx
+;Set the source
 call calcsource
 ;Set the size
-push ax
 mov al, 0x1
-;Load
+;Load a sector
 mov ah, 0x2
 int 0x13
+;Load the loop counter and the source from the stack
+pop cx
 pop ax
 ;Set the next sector
 add ax, 0x1
 add bx, word [sectorsize]
-pop cx
-loop loadroot
+;Load the next sector
+loop loadrootsector
 
 ;Search the root for the system entry
 ;Set DI to the root
 mov di, buffer
-;Initialise the search loop
+;Set the number of root entries
 mov cx, word [rootentries]
+;Set the entry pointer
 mov ax, 0x0
+;Store the loop counter in the stack
 search:
-;Store CX in the stack
 push cx
 ;Check for the system entry
-mov si, sysfile
+mov si, file
 mov cx, 0xb
 rep cmpsb
-je loadentry
-;Set DI to the next entry
+je loadfat
+;Set DI at the next entry
 add ax, 0x20
 mov di, buffer
 add di, ax
-;Load CX from the stack
+;Load the loop counter from the stack
 pop cx
+;Search the next entry
 loop search
 
-;Print an error message if the system is not found
-mov si, errormsg
-printerror:
+;Print an error message and hang if the system is not found
+;Set SI at the file error message
+mov si, filerrormsg
 ;Load a character
+printstr:
 lodsb
 ;Check for the string end
 cmp al, 0x0
@@ -124,62 +137,61 @@ je $
 ;Print the character
 mov ah, 0xe
 int 0x10
-;Repeat
-jmp printerror
+;Print the next character
+jmp printstr
 
-;Load the system entry
-loadentry:
+;Load the FAT
 ;Load CX from the stack
+loadfat:
 pop cx
-;Store the first cluster
-mov ax, word [es:di+0xf]
-mov word [cluster], ax
+;Store the address of the first cluster
+mov ax, [di + 0xf]
+mov [cluster], ax
 ;Set the source
-mov ax, 0x1
+mov ax, [reservedsectors]
 call calcsource
 ;Set the destination
-mov di, buffer
-mov bx, di
+mov bx, buffer
 ;Set the size
 mov ax, [sectorsperfat]
-;Load
+;Load the FAT
 mov ah, 0x2
 int 0x13
 
 ;Load a cluster
 loadcluster:
 ;Set the source
-pop cx
-pop bx
 mov ax, word [cluster]
 sub ax, 0x2
 mul byte [clustersize]
-add ax, bx
-add ax, cx
-push bx
-push cx
+add ax, [datastart]
 ;Set the destination
 mov bx, word [pointer]
-;Load a sector
+;Set the size
 mov ch, 0x0
 mov cl, byte [clustersize]
-loadsector:
+;Store the loop counter in the stack
+loadclustersector:
 push cx
+;Set the source
 call calcsource
 ;Set the size
 push ax
 mov al, 0x1
-;Load
+;Load a sector
 mov ah, 0x2
 int 0x13
 pop ax
 ;Set the next sector
 add ax, 0x1
-add bx, word [sectorsize]
+add bx, [sectorsize]
+;Load the loop counter from the stack
 pop cx
-loop loadsector
+;Load the next sector
+loop loadclustersector
 
 ;Calculate the next cluster
+;Check if the cluster is even or odd
 mov ax, [cluster]
 mov dx, 0x0
 mov bx, 0x3
@@ -188,67 +200,87 @@ mov bx, 0x2
 div bx
 mov si, buffer
 add si, ax
-mov ax, word [ds:si]
+mov ax, word [si]
 or dx, dx
 jz even
-odd:
-shr ax, 1
-shr ax, 1
-shr ax, 1
-shr ax, 1
+;If the cluster is odd shift out the first four bits
+times 0x4 shr ax, 0x1
 jmp contcalc
+;If the cluster is even mask out the final four bits
 even:
 and ax, 0xfff
 contcalc:
-mov word [cluster], ax
+;Check for the file end
 cmp ax, 0xff8
 jge boot
+;Store the address of the next cluster
+mov word [cluster], ax
+;Set the destination of the next cluster
 mov ax, [sectorsize]
 mul word [clustersize]
 add word [pointer], ax
+;Load the next cluster
 jmp loadcluster
 
-;Clear the stack and boot the system
+;Boot the system
+;Pass the boot drive number to the system
 boot:
-;Clear
-pop cx
-pop bx
-;Pass the drive number to the system
 mov dl, byte [drive]
-;Boot
+;Boot the system
 jmp 0x0:0x500
 
 ;Data
-drive    db 0x0
-sysfile  db "SYSTEM  BIN"
-errormsg db "System not found", 0xd, 0xa, 0x0
-cluster  dw 0x0
-pointer  dw 0x500
+drive       db 0x0
+rootstart   dw 0x0
+rootsectors dw 0x0
+datastart   dw 0x0
+file        db "SYSTEM  BIN"
+filerrormsg db "System not found", 0xd, 0xa, 0x0
+cluster     dw 0x0
+pointer     dw 0x500
+
+;***
 
 ;Calculate the source arguments for loading data from the disk
 calcsource:
+
+;Store AX and BX in the stack
 push ax
 push bx
+
+;Calculate the cylinder, head, and sector
+;Store the logical sector in BX
 mov bx, ax
+;Calculate the sector
 mov dx, 0x0
 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]
 mov dx, 0x0
-div word [sides]
-mov dh, dl
-mov ch, al
+div word [heads]
+mov dh, dl ;Head
+mov ch, al ;Cylinder
+
+;Load the boot drive number
+mov dl, byte [drive]
+
+;Load BX and AX from the stack
 pop bx
 pop ax
-mov dl, byte [drive]
+
+;Return
 ret
 
-;Pad the binary to a full sector and make the disk bootable
+;***
+
 ;Padding
 times 0x1fe-($-$$) db 0x0
+
 ;Boot signature
 dw 0xaa55
 
diff --git a/src/ECHO.ASM b/src/ECHO.ASM
index e5ce8ad..0b51c81 100644
--- a/src/ECHO.ASM
+++ b/src/ECHO.ASM
@@ -1,12 +1,14 @@
-CPU 8086
-ORG 0x3000
+cpu 8086
+org 0x3000
 
-;Echo the tail
 ;Check for an empty tail
 cmp byte [si], 0x0
 je done
-;Echo
+
+;Print the message
 mov ah, 0x2
 int 0x21
+
+;Return to the system
 done:
 int 0x20
diff --git a/src/HELLO.ASM b/src/HELLO.ASM
index 21c9d84..e05c35d 100644
--- a/src/HELLO.ASM
+++ b/src/HELLO.ASM
@@ -1,10 +1,12 @@
-CPU 8086
-ORG 0x3000
+cpu 8086
+org 0x3000
 
 ;Print a hello world.
 mov si, hello
 mov ah, 0x2
 int 0x21
+
+;Return to the system
 int 0x20
 
 ;Data
diff --git a/src/LIST.ASM b/src/LIST.ASM
index a41a161..06625d3 100644
--- a/src/LIST.ASM
+++ b/src/LIST.ASM
@@ -1,7 +1,5 @@
-CPU 8086
-ORG 0x3000
-
-;List the files on a drive
+cpu 8086
+org 0x3000
 
 ;Store the drive number
 mov [drive], dl
@@ -21,45 +19,36 @@ je changedrive
 ;Print an error message
 jmp driverror
 changedrive:
+;Get the BIOS equipment list
+int 0x11
+;Get the number of floppy drives
+times 0x6 shr ax, 0x1
+and ax, 0x3
+inc ax
+;Set the loop and drive letter counters and the drive letter and number
+mov cx, ax
+mov di, driveletters
+mov al, [si]
+mov dl, 0x0
 ;Check which drive to change to
-cmp byte [si], "a"
-je cha
-cmp byte [si], "A"
-je cha
-cmp byte [si], "b"
-je chb
-cmp byte [si], "B"
-je chb
-cmp byte [si], "c"
-je chc
-cmp byte [si], "C"
-je chc
-cmp byte [si], "d"
-je chd
-cmp byte [si], "D"
-je chd
+checkdrive:
+cmp al, [di]
+je contchdrive
+inc di
+cmp al, [di]
+je contchdrive
+inc di
+inc dl
+loop checkdrive
 ;Print an error message
 jmp driverror
-;Change
-cha:
-mov dl, 0x0
-mov byte [drive], dl
-jmp loadvalues
-chb:
-mov dl, 0x1
-mov byte [drive], dl
-jmp loadvalues
-chc:
-mov dl, 0x2
-mov byte [drive], dl
-jmp loadvalues
-chd:
-mov dl, 0x3
-mov byte [drive], dl
+;Change the drive
+contchdrive:
+mov [drive], dl
 
 ;Load the disk description table
-loadvalues:
 ;Set the source
+loadvalues:
 mov dl, [drive]
 mov ch, 0x0
 mov dh, 0x0
@@ -69,62 +58,68 @@ mov si, buffer
 mov bx, si
 ;Set the size
 mov al, 0x1
-;Load
+;Load the disk description table
 mov ah, 0x2
 int 0x13
 jc diskerror
 
 ;Store the disk values used for the rest of the call
-mov ax, word [buffer + 0xb]
-mov word [sectorsize], ax
-mov ax, word [buffer + 0xe]
-mov word [bootsectors], ax
-mov al, byte [buffer + 0x10]
-mov byte [fats], al
-mov ax, word [buffer + 0x11]
-mov word [rootentries], ax
-mov ax, word [buffer + 0x16]
-mov word [sectorsperfat], ax
-mov ax, word [buffer + 0x18]
-mov word [sectorspertrack], ax
-mov ax, word [buffer + 0x1a]
-mov word [sides], ax
+mov ax, [buffer + 0xb]
+mov [sectorsize], ax
+mov ax, [buffer + 0xe]
+mov [reservedsectors], ax
+mov al, [buffer + 0x10]
+mov [fats], al
+mov ax, [buffer + 0x11]
+mov [rootentries], ax
+mov ax, [buffer + 0x16]
+mov [sectorsperfat], ax
+mov ax, [buffer + 0x18]
+mov [sectorspertrack], ax
+mov ax, [buffer + 0x1a]
+mov [heads], ax
 
-;Load the root
-;Set the source
+;Calculate and store variables not found in the BPB
+;Start of the root
 mov ah, 0x0
 mov al, [fats]
 mul word [sectorsperfat]
-add ax, [bootsectors]
-push ax
-;Set the destination
-mov si, buffer
-mov bx, si
-;Set the size
+add ax, [reservedsectors]
+mov [rootstart], ax
+;Size of the root in sectors
 mov ax, [rootentries]
 mov dx, 0x20
 mul dx
 mov dx, 0x0
 div word [sectorsize]
-mov cx, ax
-pop ax
+mov [rootsectors], ax
+
+;Load the root
+;Set the source
+mov ax, [rootstart]
+;Set the destination
+mov si, buffer
+mov bx, si
+;Set the size
+mov cx, [rootsectors]
+;Store the source and the loop counter in the stack
+loadrootsector:
 push ax
 push cx
-loadroot:
-push cx
+;Set the source
 call calcsource
 ;Set the size
-push ax
 mov al, 0x1
-;Load
+;Load a sector
 mov ah, 0x2
 int 0x13
+;Load the loop counter and the source from the stack
+pop cx
 pop ax
 ;Set the next sector
 add ax, 0x1
 add bx, word [sectorsize]
-pop cx
-loop loadroot
+loop loadrootsector
 
 ;List
 ;Set SI to the root
@@ -133,8 +128,8 @@ mov si, buffer
 mov cx, word [rootentries]
 mov ax, 0x0
 mov bl, 0x17
-loop:
 ;Store CX in the stack
+loop:
 push cx
 ;Check for an empty entry
 cmp byte [si], 0xe5
@@ -178,8 +173,8 @@ pop ax
 cmp bl, 0x0
 jz page
 dec bl
-skip:
 ;Set SI to the next entry
+skip:
 add ax, 0x20
 mov si, buffer
 add si, ax
@@ -190,6 +185,8 @@ page:
 push ax
 mov ah, 0x0
 int 0x16
+cmp al, 0x1b
+je done
 pop ax
 mov bl, 0x17
 jmp skip
@@ -212,35 +209,56 @@ jmp done
 ;Data
 drive           db 0x0
 sectorsize      dw 0x0 ;bytes
-bootsectors     dw 0x0
+reservedsectors dw 0x0
 fats            db 0x0
 rootentries     dw 0x0
 sectorsperfat   dw 0x0
 sectorspertrack dw 0x0
-sides           dw 0x0
+heads           dw 0x0
+rootstart       dw 0x0
+rootsectors     dw 0x0
+driveletters    db "AaBbCcDd"
 driverrormsg    db "Drive not found", 0x0
 diskerrormsg    db "Unable to read disk", 0x0
 
+;***
+
 ;Calculate the source arguments for loading data from the disk
 calcsource:
+
+;Store AX and BX in the stack
 push ax
 push bx
+
+;Calculate the cylinder, head, and sector
+;Store the logical sector in BX
 mov bx, ax
+;Calculate the sector
 mov dx, 0x0
 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]
 mov dx, 0x0
-div word [sides]
-mov dh, dl
-mov ch, al
+div word [heads]
+mov dh, dl ;Head
+mov ch, al ;Cylinder
+
+;Load the drive number
+mov dl, byte [drive]
+
+;Load BX and AX from the stack
 pop bx
 pop ax
-mov dl, byte [drive]
+
+;Return
 ret
 
+;***
+
 ;Buffer
 buffer:
diff --git a/src/LOADF.INC b/src/LOADF.INC
index f7665b5..83aabe0 100644
--- a/src/LOADF.INC
+++ b/src/LOADF.INC
@@ -8,7 +8,7 @@
 
 loadf:
 
-;Store the initial registers in the stack
+;Store BX, DX, SI, and DI in the stack
 push bx
 push dx
 push si
@@ -22,24 +22,28 @@ mov byte [.drive], dl
 ;Change the drive if needed
 ;Check for a drive specification
 cmp byte [si + 0x1], ":"
-jne .start
+jne .convert
+;Get the BIOS equipment list
+int 0x11
+;Get the number of floppy drives
+times 0x6 shr ax, 0x1
+and ax, 0x3
+inc ax
+;Set the loop and drive letter counters and the drive letter and number
+mov cx, ax
+mov di, driveletters
+mov al, [si]
+mov dl, 0x0
 ;Check which drive to change to
-cmp byte [si], "a"
-je .cha
-cmp byte [si], "A"
-je .cha
-cmp byte [si], "b"
-je .chb
-cmp byte [si], "B"
-je .chb
-cmp byte [si], "c"
-je .chc
-cmp byte [si], "C"
-je .chc
-cmp byte [si], "d"
-je .chd
-cmp byte [si], "D"
-je .chd
+.checkdrive:
+cmp al, [di]
+je .contchdrive
+inc di
+cmp al, [di]
+je .contchdrive
+inc di
+inc dl
+loop .checkdrive
 ;Set AL to 0x1, CX to 0x0, and print an error message
 mov si, .driverrormsg
 mov ah, 0x2
@@ -47,57 +51,41 @@ int 0x21
 mov al, 0x1
 mov cx, 0x0
 jmp .done
-;Change
-.cha:
-mov dl, 0x0
-mov byte [.drive], dl
-jmp .drivechanged
-.chb:
-mov dl, 0x1
-mov byte [.drive], dl
-jmp .drivechanged
-.chc:
-mov dl, 0x2
-mov byte [.drive], dl
-jmp .drivechanged
-.chd:
-mov dl, 0x3
-mov byte [.drive], dl
-.drivechanged:
+;Change the drive
+.contchdrive:
+mov [.drive], dl
+;Move to the file name
 add si, 0x2
 
-.start:
-
 ;Set DI at .file and initialise it with spaces
+.convert:
 mov di, .file
 mov cx, 0xb
 mov al, 0x20
 rep stosb
 sub di, 0xb
 
-;Convert .file into FAT formatting
-
-;Initialise the length counter for the main part of the file name
+;Convert the main part of the file name into FAT format
+;Set the length counter
 mov bl, 0x8
-
-;Convert the main part of the file name
-.nameloop:
 ;Load a character
+.nameloop:
 lodsb
 ;Check for a period
 cmp al, 0x2e
 je .initext
 ;Check for everything else and convert to upper case
 call .checkconv
+;Load the next character
 jmp .nameloop
 
-;Convert the extension
+;Convert the extension into FAT format
+;Set DI and the length counter for the extension
 .initext:
-;Set DI and initialise the length counter for the extension
 mov bl, 0x3
 mov di, .file+0x8
-.extloop:
 ;Load a character
+.extloop:
 lodsb
 ;Check for a period
 push ax
@@ -106,6 +94,7 @@ je .error
 pop ax
 ;Check for everything else and convert to upper case
 call .checkconv
+;Load the next character
 jmp .extloop
 ;Set AL to 0x4, CX to 0x0, and print an error message
 .error:
@@ -118,7 +107,6 @@ mov cx, 0x0
 jmp .done
 
 ;Find and load the file
-
 .load:
 pop ax
 
@@ -133,7 +121,7 @@ mov si, buffer
 mov bx, si
 ;Set the size
 mov al, 0x1
-;Load
+;Load the disk description table
 mov ah, 0x2
 int 0x13
 jnc .storevalues
@@ -147,79 +135,91 @@ jmp .done
 
 ;Store the disk values used for the rest of the call
 .storevalues:
-mov ax, word [buffer + 0xb]
-mov word [.sectorsize], ax
-mov al, byte [buffer + 0xd]
-mov byte [.clustersize], al
-mov ax, word [buffer + 0xe]
-mov word [.bootsectors], ax
-mov al, byte [buffer + 0x10]
-mov byte [.fats], al
-mov ax, word [buffer + 0x11]
-mov word [.rootentries], ax
-mov ax, word [buffer + 0x16]
-mov word [.sectorsperfat], ax
-mov ax, word [buffer + 0x18]
-mov word [.sectorspertrack], ax
-mov ax, word [buffer + 0x1a]
-mov word [.sides], ax
+mov ax, [buffer + 0xb]
+mov [.sectorsize], ax
+mov al, [buffer + 0xd]
+mov [.clustersize], al
+mov ax, [buffer + 0xe]
+mov [.reservedsectors], ax
+mov al, [buffer + 0x10]
+mov [.fats], al
+mov ax, [buffer + 0x11]
+mov [.rootentries], ax
+mov ax, [buffer + 0x16]
+mov [.sectorsperfat], ax
+mov ax, [buffer + 0x18]
+mov [.sectorspertrack], ax
+mov ax, [buffer + 0x1a]
+mov [.heads], ax
 
-;Load the root
-;Set the source
+;Calculate and store variables not found in the BPB
+;Start of the root
 mov ah, 0x0
 mov al, [.fats]
 mul word [.sectorsperfat]
-add ax, [.bootsectors]
-push ax
-;Set the destination
-mov si, buffer
-mov bx, si
-;Set the size
+add ax, [.reservedsectors]
+mov [.rootstart], ax
+;Size of the root in sectors
 mov ax, [.rootentries]
 mov dx, 0x20
 mul dx
 mov dx, 0x0
 div word [.sectorsize]
-mov cx, ax
-pop ax
+mov [.rootsectors], ax
+;Start of data
+add ax, [.rootstart]
+mov [.datastart], ax
+
+;Load the root
+;Set the source
+mov ax, [.rootstart]
+;Set the destination
+mov si, buffer
+mov bx, si
+;Set the size
+mov cx, [.rootsectors]
+;Store the source and the loop counter in the stack
+.loadrootsector:
 push ax
 push cx
-.loadroot:
-push cx
+;Set the source
 call .calcsource
 ;Set the size
-push ax
 mov al, 0x1
-;Load
+;Load a sector
 mov ah, 0x2
 int 0x13
+;Load the loop counter and the source from the stack
+pop cx
 pop ax
 ;Set the next sector
 add ax, 0x1
 add bx, word [.sectorsize]
-pop cx
-loop .loadroot
+;Load the next sector
+loop .loadrootsector
 
 ;Search the root for the file entry
 ;Set DI to the root
 mov di, buffer
-;Initialise the search loop
+;Set the number of root entries
 mov cx, word [.rootentries]
+;Set the entry pointer
 mov ax, 0x0
+;Store the loop counter in the stack
 .search:
-;Store CX in the stack
 push cx
 ;Check for the file entry
 mov si, .file
 mov cx, 0xb
 rep cmpsb
 je .checksize
-;Set DI to the next entry
+;Set DI at the next entry
 add ax, 0x20
 mov di, buffer
 add di, ax
-;Load CX from the stack
+;Load the loop counter from the stack
 pop cx
+;Search the next entry
 loop .search
 ;Set AL to 0x4, CX to 0x0, and print an error message
 mov si, .filerrormsg
@@ -227,11 +227,11 @@ mov ah, 0x2
 int 0x21
 mov al, 0x4
 mov cx, 0x0
-jmp .clearstack
+jmp .done
 
 ;Check and store the file size
-.checksize:
 ;Load CX from the stack
+.checksize:
 pop cx
 ;Check for files larger than 64 KiB
 cmp word [di + 0x13], 0x0
@@ -259,61 +259,58 @@ mov ah, 0x2
 int 0x21
 mov al, 0x8
 mov cx, 0x0
-jmp .clearstack
+jmp .done
 
 ;Load the FAT
 .loadfat:
-;Store the first cluster of the file
-mov ax, word [di + 0xf]
-mov word [.cluster], ax
+;Store the address of the first cluster
+mov ax, [di + 0xf]
+mov [.cluster], ax
 ;Set the source
-mov ax, 0x1
+mov ax, [.reservedsectors]
 call .calcsource
 ;Set the destination
-mov di, buffer
-mov bx, di
+mov bx, buffer
 ;Set the size
 mov ax, [.sectorsperfat]
-;Load
+;Load the FAT
 mov ah, 0x2
 int 0x13
 
-;Load the file
-
 ;Load a cluster
 .loadcluster:
 ;Set the source
-pop cx
-pop bx
 mov ax, word [.cluster]
 sub ax, 0x2
 mul byte [.clustersize]
-add ax, bx
-add ax, cx
-push bx
-push cx
+add ax, [.datastart]
 ;Set the destination
 mov bx, word [.pointer]
-;Load a sector
+;Set the size
 mov ch, 0x0
 mov cl, byte [.clustersize]
+;Store the loop counter in the stack
 .loadsector:
 push cx
+;Set the source
 call .calcsource
 ;Set the size
 push ax
 mov al, 0x1
-;Load
+;Load a sector
 mov ah, 0x2
 int 0x13
 pop ax
 ;Set the next sector
 add ax, 0x1
 add bx, word [.sectorsize]
+;Load the loop counter from the stack
 pop cx
+;Load the next sector
 loop .loadsector
 
 ;Calculate the next cluster
+;Check if the cluster is even or odd
 mov ax, [.cluster]
 mov dx, 0x0
 mov bx, 0x3
@@ -322,23 +319,26 @@ mov bx, 0x2
 div bx
 mov si, buffer
 add si, ax
-mov ax, word [ds:si]
+mov ax, word [si]
 or dx, dx
 jz .even
-shr ax, 1
-shr ax, 1
-shr ax, 1
-shr ax, 1
+;If the cluster is odd shift out the first four bits
+times 0x4 shr ax, 0x1
 jmp .contcalc
+;If the cluster is even mask out the final four bits
 .even:
 and ax, 0xfff
 .contcalc:
-mov word [.cluster], ax
+;Check for the file end
 cmp ax, 0xff8
 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]
 add word [.pointer], ax
+;Load the next cluster
 jmp .loadcluster
 
 ;Set AL to 0x0 and load the file size to CX if the load was succesful
@@ -347,13 +347,9 @@ mov al, 0x0
 mov cx, [.size]
 
 ;Clear the stack
-.clearstack:
-pop bx
-pop bx
-
 .done:
 
-;Load the initial registers from the stack
+;Load DI, SI, DX, and BX from the stack
 pop di
 pop si
 pop dx
@@ -362,18 +358,22 @@ pop bx
 ;Set AH to its initial value
 mov ah, 0x0
 
+;Return
 iret
 
 ;Data
 .drive           db 0x0
 .sectorsize      dw 0x0 ;bytes
 .clustersize     db 0x0 ;sectors
-.bootsectors     dw 0x0
+.reservedsectors dw 0x0
 .fats            db 0x0
 .rootentries     dw 0x0
 .sectorsperfat   dw 0x0
 .sectorspertrack dw 0x0
-.sides           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
@@ -383,8 +383,12 @@ iret
 .filerrormsg     db "File or command not found", 0x0
 .sizerrormsg     db "Not enough memory", 0x0
 
+;***
+
 ;Check the file name and convert to upper case
 .checkconv:
+
+;Check for the string end, length limit, and invalid characters
 ;Check for the string end
 cmp al, 0x0
 je .load
@@ -416,6 +420,8 @@ jmp .error
 .contcheck3:
 cmp al, 0x7c
 je .error
+
+;Check for lower case and convert it to upper case
 ;Check for lower case
 cmp al, 0x61
 jl .storech
@@ -423,30 +429,50 @@ cmp al, 0x7a
 jg .storech
 ;Convert lower to upper case
 sub al, 0x20
-.storech:
+
 ;Store the character
+.storech:
 stosb
+
 ;Decrease the counter
 dec bl
+
+;Return
 ret
 
+;***
+
 ;Calculate the source arguments for loading data from the disk
 .calcsource:
+
+;Store AX and BX in the stack
 push ax
 push bx
+
+;Calculate the cylinder, head, and sector
+;Store the logical sector in BX
 mov bx, ax
+;Calculate the sector
 mov dx, 0x0
 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]
 mov dx, 0x0
-div word [.sides]
-mov dh, dl
-mov ch, al
+div word [.heads]
+mov dh, dl ;Head
+mov ch, al ;Cylinder
+
+;Load the drive number
+mov dl, byte [.drive]
+
+;Load BX and AX from the stack
 pop bx
 pop ax
-mov dl, byte [.drive]
+
+;Return
 ret
diff --git a/src/PRINT.ASM b/src/PRINT.ASM
index 17503fb..7e571b2 100644
--- a/src/PRINT.ASM
+++ b/src/PRINT.ASM
@@ -1,5 +1,5 @@
-CPU 8086
-ORG 0x3000
+cpu 8086
+org 0x3000
 
 ;Load a file and print it
 
@@ -11,17 +11,16 @@ sti
 ;Check for an empty tail
 ;Check
 cmp byte [si], 0x0
-jne start
+jne extract
 ;Print an error message and abort if the tail is empty
 mov si, errormsg
 mov ah, 0x2
 int 0x21
 je done
 
-start:
-
 ;Find the end of the filename and add a null if needed
 ;Set DI at the tail
+extract:
 mov di, si
 findend:
 ;Check for the string end
@@ -32,13 +31,14 @@ cmp byte [di], 0x20
 je addnull
 inc di
 jmp findend
+;Add a null
 addnull:
 mov al, 0x0
 stosb
 
 ;Load the file
-load:
 ;Load
+load:
 mov bx, stack + 0x100
 mov ah, 0x0
 int 0x22
@@ -52,8 +52,8 @@ mov bh, 0x0
 mov bl, 0x18
 mov dl, 0x50
 mov si, stack + 0x100
-print:
 ;Decrease the character counter
+print:
 dec dl
 ;Load the current character
 lodsb
@@ -66,8 +66,8 @@ je linecount
 ;Check for a soft line end
 cmp dl, 0x0
 je linecount
-contprint:
 ;Check paging
+contprint:
 cmp bl, 0x0
 jz page
 ;Repeat for the next character
@@ -83,15 +83,19 @@ page:
 push ax
 mov ah, 0x0
 int 0x16
+cmp al, 0x1b
+je done
 pop ax
 mov bl, 0x18
 mov dl, 0x50
 loop print
 
+;Return to the system
 done:
 int 0x20
 
 ;Data
 errormsg db "File not found", 0x0
 
+;Stack
 stack:
diff --git a/src/PRINTLN.INC b/src/PRINTLN.INC
index ac5dc55..35b1355 100644
--- a/src/PRINTLN.INC
+++ b/src/PRINTLN.INC
@@ -1,5 +1,4 @@
 ;Print a string ending in a null from SI followed by a CRLF.
-
 println:
 
 ;Print the string
@@ -9,4 +8,5 @@ int 0x21
 ;Print a CRLF
 call printcrlf
 
+;Return
 iret
diff --git a/src/PRINTSTR.INC b/src/PRINTSTR.INC
index 57fde6b..4cf7346 100644
--- a/src/PRINTSTR.INC
+++ b/src/PRINTSTR.INC
@@ -1,14 +1,13 @@
 ;Print a string ending in a null from SI.
-
 printstr:
 
-;Store the initial registers in the stack
+;Store AX and SI in the stack
 push ax
 push si
 
 ;Print the string
-.loop:
 ;Load the current character
+.loop:
 lodsb
 ;Check for the string end
 cmp al, 0x0
@@ -16,13 +15,13 @@ je .done
 ;Print the character
 mov ah, 0xe
 int 0x10
-;Repeat for the next character
+;Print the next character
 jmp .loop
 
-.done:
-
 ;Load the initial registers from the stack
+.done:
 pop si
 pop ax
 
+;Return
 iret
diff --git a/src/READLN.INC b/src/READLN.INC
index 59e4f44..a2db6c9 100644
--- a/src/READLN.INC
+++ b/src/READLN.INC
@@ -1,6 +1,5 @@
 ;Read a string ending in a null of at most AL characters to DI until a
 ;return and print a CRLF.
-
 readln:
 
 ;Read the string
@@ -10,4 +9,5 @@ int 0x21
 ;Print a CRLF
 call printcrlf
 
+;Return
 iret
diff --git a/src/READSTR.INC b/src/READSTR.INC
index cd0bef8..e5aca43 100644
--- a/src/READSTR.INC
+++ b/src/READSTR.INC
@@ -1,9 +1,8 @@
 ;Read a string ending in a null of at most AL characters to DI until a
 ;return.
-
 readstr:
 
-;Store the initial registers in the stack
+;Store AX, BX, CX, DX, and DI in the stack
 push ax
 push bx
 push cx
@@ -26,12 +25,11 @@ mov ah, 0xf
 int 0x10
 dec ah
 mov [.lastcolumn], ah
-;Initialise the cursor pointer in BL and clear BH
+;Set the cursor pointer in BL and clear BH
 mov bx, 0x1
 
-.loop:
-
 ;Read a keypress
+.loop:
 mov ah, 0x0
 int 0x16
 
@@ -87,29 +85,27 @@ jmp .loop
 ;Check for the input beginning
 cmp bl, 0x1
 je .loop
-;Move
+;Move the cursor
 call .prevchar
 dec di
 dec bl
 jmp .loop
 
-;Finish reading the string
-.return:
-
 ;Check for and remove trailing spaces
 ;Go to the end of the input
+.return:
 pop ax
 mov bh, 0x0
 sub ax, bx
 push di
 add di, ax
+;Check for trailing spaces
 .findtrailing:
-;Check
 cmp byte [di], 0x20
 je .deltrailing
 jmp .end
+;Remove trailing spaces
 .deltrailing:
-;Remove
 mov al, 0x0
 stosb
 sub di, 0x2
@@ -128,49 +124,57 @@ inc di
 inc bl
 jmp .findend
 
+;Load DI, DX, CX, BX, and AX from the stack
 .done:
-
-;Load the initial registers from the stack
 pop di
 pop dx
 pop cx
 pop bx
 pop ax
 
+;Return
 iret
 
 ;Data
 .lastcolumn db 0x0
 
-;Move the cursor forward within a line
+;***
+
+;Move the cursor forward
 .nextchar:
+
 ;Get the cursor position
 mov ah, 0x3
 int 0x10
+
 ;Check for the end of the line
 cmp dl, [.lastcolumn]
 je .nextln
-;Move
+
+;Move the cursor forward within a line
 inc dl
 mov ah, 0x2
 int 0x10
+
+;Return
 ret
 
 ;Move the cursor to the beginning of the next line
-.nextln:
 ;Check if the current line is the last on screen
+.nextln:
 cmp dh, 0x18
 je .scroll
-;Move
+;Move the cursor
 mov ah, 0x2
 inc dh
 mov dl, 0x0
 int 0x10
+
+;Return
 ret
 
 ;Scroll the screen up by one line
 .scroll:
-;Scroll
 mov ah, 0x6
 mov al, 0x1
 mov bh, 0x7
@@ -179,25 +183,35 @@ mov cl, 0x0
 mov dh, 0x18
 mov dl, [.lastcolumn]
 int 0x10
+
 ;Move to the beginning of the new line
 mov ah, 0x2
 mov bh, 0x0
 mov dl, 0x0
 int 0x10
+
+;Return
 ret
 
-;Move the cursor backward within a line
+;***
+
+;Move the cursor backward
 .prevchar:
+
 ;Get the cursor position
 mov ah, 0x3
 int 0x10
+
 ;Check for the beginning of the line
 cmp dl, 0x0
 je .prevln
-;Move
+
+;Move the cursor backward within a line
 dec dl
 mov ah, 0x2
 int 0x10
+
+;Return
 ret
 
 ;Move the cursor to the end of the previous line
@@ -206,4 +220,6 @@ mov ah, 0x2
 dec dh
 mov dl, [.lastcolumn]
 int 0x10
+
+;Return
 ret
diff --git a/src/SYSTEM.ASM b/src/SYSTEM.ASM
index 4bd125e..22079c1 100644
--- a/src/SYSTEM.ASM
+++ b/src/SYSTEM.ASM
@@ -1,6 +1,7 @@
-CPU 8086
-ORG 0x500
+cpu 8086
+org 0x500
 
+;Jump to the code
 jmp start
 
 ;Interrupt handler
@@ -25,17 +26,16 @@ je loadf
 ;To do: savef
 iret
 
-;System calls
+;System call includes
 %include "PRINTSTR.INC"
 %include "READSTR.INC"
 %include "PRINTLN.INC"
 %include "READLN.INC"
 %include "LOADF.INC"
 
-start:
-
 ;Set up the interrupt vectors
 ;Interrupt 0x20 offset
+start:
 mov ax, int0x20
 mov [0x80], ax
 ;Interrupt 0x21 offset
@@ -110,10 +110,10 @@ mov cx, 0xe
 mov al, 0x20
 rep stosb
 sub di, 0xe
-;Initialise the length counter
+;Set the length counter
 mov bl, 0xa
-specloop:
 ;Load a character
+specloop:
 lodsb
 ;Check for the string end
 cmp al, 0x0
@@ -128,16 +128,18 @@ je cmderror
 stosb
 ;Decrease the counter
 dec bl
+;Extract the next character
 jmp specloop
-;Add extension to the name
+;Store the start of the command tail in the stack
 addext:
 push si
+;Add extension to the specification
 mov si, extension
 mov cx, 0x5
 rep movsb
 
 ;Load and execute the program
-;Load
+;Load the program
 mov bx, 0x3000
 mov si, program
 mov ah, 0x0
@@ -149,9 +151,43 @@ jne shell
 mov dl, [drive]
 pop si
 call ignoreleading
-;Execute
+;Execute the program
 jmp 0x3000
 
+;Change the drive
+;Get the BIOS equipment list
+changedrive:
+int 0x11
+;Get the number of floppy drives
+times 0x6 shr ax, 0x1
+and ax, 0x3
+inc ax
+;Set the loop and drive letter counters and the drive letter and number
+mov cx, ax
+mov di, driveletters
+mov al, [si]
+mov dl, 0x0
+;Check which drive to change to
+checkdrive:
+cmp al, [di]
+je contchdrive
+inc di
+cmp al, [di]
+je contchdrive
+inc di
+inc dl
+loop checkdrive
+;Print a drive error message and return to the shell
+mov si, driverrormsg
+mov ah, 0x2
+int 0x21
+jmp shell
+;Change the drive
+contchdrive:
+mov [drive], dl
+call setdriveletter
+jmp shell
+
 ;Print a command error message and return to the shell
 cmderror:
 mov si, cmderrormsg
@@ -159,56 +195,11 @@ mov ah, 0x2
 int 0x21
 jmp shell
 
-;Change the drive
-changedrive:
-;Check which drive to change to
-cmp byte [si], "a"
-je cha
-cmp byte [si], "A"
-je cha
-cmp byte [si], "b"
-je chb
-cmp byte [si], "B"
-je chb
-cmp byte [si], "c"
-je chc
-cmp byte [si], "C"
-je chc
-cmp byte [si], "d"
-je chd
-cmp byte [si], "D"
-je chd
-;Print a drive error message and return to the shell
-mov si, driverrormsg
-mov ah, 0x2
-int 0x21
-jmp shell
-;Change
-cha:
-mov dl, 0x0
-mov [drive], dl
-call setdriveletter
-jmp shell
-chb:
-mov dl, 0x1
-mov [drive], dl
-call setdriveletter
-jmp shell
-chc:
-mov dl, 0x2
-mov [drive], dl
-call setdriveletter
-jmp shell
-chd:
-mov dl, 0x3
-mov [drive], dl
-call setdriveletter
-jmp shell
-
 ;Data
 welcomemsg   db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
 drive        db 0x0
 driveletter  db "?:", 0x0
+driveletters db "AaBbCcDd"
 prompt       db "> ", 0x0
 input        times 0x4c db 0x0
 program      times 0xf db 0x0
@@ -216,53 +207,70 @@ extension    db ".BIN", 0x0
 cmderrormsg  db "File or command not found", 0x0
 driverrormsg db "Drive not found", 0x0
 
+;***
+
 ;Set the drive letter
 setdriveletter:
+
+;Set the drive number and letter counters
+mov dh, 0x0
+mov si, driveletters
+
 ;Check the drive number
-cmp dl, 0x0
-je .seta
-cmp dl, 0x1
-je .setb
-cmp dl, 0x2
-je .setc
-cmp dl, 0x3
-je .setd
-ret
-;Set
-.seta:
-mov byte [driveletter], "A"
-ret
-.setb:
-mov byte [driveletter], "B"
-ret
-.setc:
-mov byte [driveletter], "C"
-ret
-.setd:
-mov byte [driveletter], "D"
+.checkdrive:
+cmp dl, dh
+je .set
+add si, 0x2
+inc dh
+jmp .checkdrive
+
+;Set the drive letter
+.set:
+mov al, [si]
+mov byte [driveletter], al
+
+;Return
 ret
 
+;***
+
 ;Ignore leading spaces in the command and its tail
 ignoreleading:
+
+;Check for a space
 lodsb
 cmp al, 0x20
 je ignoreleading
+
+;Set SI to the first non-space character
 dec si
+
+;Return
 ret
 
+;***
+
 ;Print a CRLF
 printcrlf:
-;Store the initial registers in the stack
+
+;Store SI in the stack
 push si
+
 ;Print the CRLF
 mov si, .crlf
 mov ah, 0x0
 int 0x21
-;Load the initial registers from the stack
+
+;Load SI from the stack
 pop si
+
+;Return
 ret
+
 ;Data
 .crlf db 0xd, 0xa, 0x0
 
+;***
+
 ;File system buffer
 buffer: