diff --git a/cmd/catalog.go b/cmd/catalog.go
index 1820afd..9c177b9 100644
--- a/cmd/catalog.go
+++ b/cmd/catalog.go
@@ -37,11 +37,7 @@ func runCat(args []string) error {
 	if len(args) < 1 || len(args) > 2 {
 		return fmt.Errorf("cat expects a disk image filename, and an optional subdirectory")
 	}
-	sd, err := disk.Open(args[0])
-	if err != nil {
-		return err
-	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.Open(args[0])
 	if err != nil {
 		return err
 	}
diff --git a/cmd/delete.go b/cmd/delete.go
index a4df421..d7977fa 100644
--- a/cmd/delete.go
+++ b/cmd/delete.go
@@ -38,11 +38,7 @@ func runDelete(args []string) error {
 	if len(args) != 2 {
 		return fmt.Errorf("delete expects a disk image filename, and a filename")
 	}
-	sd, err := disk.Open(args[0])
-	if err != nil {
-		return err
-	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.Open(args[0])
 	if err != nil {
 		return err
 	}
@@ -57,7 +53,7 @@ func runDelete(args []string) error {
 	if err != nil {
 		return err
 	}
-	_, err = sd.Write(f)
+	_, err = op.Write(f)
 	if err != nil {
 		return err
 	}
diff --git a/cmd/dump.go b/cmd/dump.go
index 78b56a9..fce649a 100644
--- a/cmd/dump.go
+++ b/cmd/dump.go
@@ -36,11 +36,7 @@ func runDump(args []string) error {
 	if len(args) != 2 {
 		return fmt.Errorf("dump expects a disk image filename, and a filename")
 	}
-	sd, err := disk.Open(args[0])
-	if err != nil {
-		return err
-	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.Open(args[0])
 	if err != nil {
 		return err
 	}
diff --git a/cmd/nakedos.go b/cmd/nakedos.go
index e4876c6..7fb1ed8 100644
--- a/cmd/nakedos.go
+++ b/cmd/nakedos.go
@@ -68,11 +68,7 @@ func runMkhello(args []string) error {
 	if start < address {
 		return fmt.Errorf("start address %d (%04X) < load address %d (%04X)", start, start, address, address)
 	}
-	sd, err := disk.Open(args[0])
-	if err != nil {
-		return err
-	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.Open(args[0])
 	if err != nil {
 		return err
 	}
@@ -118,7 +114,7 @@ func runMkhello(args []string) error {
 	if err != nil {
 		return err
 	}
-	_, err = sd.Write(f)
+	_, err = op.Write(f)
 	if err != nil {
 		return err
 	}
diff --git a/cmd/put.go b/cmd/put.go
index af6860b..f057273 100644
--- a/cmd/put.go
+++ b/cmd/put.go
@@ -42,11 +42,7 @@ func runPut(args []string) error {
 	if len(args) != 3 {
 		return fmt.Errorf("usage: put <disk image> <target filename> <source filename>")
 	}
-	sd, err := disk.Open(args[0])
-	if err != nil {
-		return err
-	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.Open(args[0])
 	if err != nil {
 		return err
 	}
@@ -76,7 +72,7 @@ func runPut(args []string) error {
 	if err != nil {
 		return err
 	}
-	_, err = sd.Write(f)
+	_, err = op.Write(f)
 	if err != nil {
 		return err
 	}
diff --git a/lib/disk/disk.go b/lib/disk/disk.go
index 18f0143..7d5d222 100644
--- a/lib/disk/disk.go
+++ b/lib/disk/disk.go
@@ -156,8 +156,8 @@ func (md MappedDisk) Write(w io.Writer) (n int, err error) {
 	return md.sectorDisk.Write(w)
 }
 
-// Open opens a disk image by filename.
-func Open(filename string) (SectorDisk, error) {
+// OpenDisk opens a disk image by filename.
+func OpenDisk(filename string) (SectorDisk, error) {
 	ext := strings.ToLower(path.Ext(filename))
 	switch ext {
 	case ".dsk":
@@ -165,3 +165,16 @@ func Open(filename string) (SectorDisk, error) {
 	}
 	return nil, fmt.Errorf("Unimplemented/unknown disk file extension %q", ext)
 }
+
+// Open opens a disk image by filename, returning an Operator.
+func Open(filename string) (Operator, error) {
+	sd, err := OpenDisk(filename)
+	if err != nil {
+		return nil, err
+	}
+	op, err := OperatorForDisk(sd)
+	if err != nil {
+		return nil, err
+	}
+	return op, nil
+}
diff --git a/lib/disk/marshal.go b/lib/disk/marshal.go
index e6204d1..c472060 100644
--- a/lib/disk/marshal.go
+++ b/lib/disk/marshal.go
@@ -1,10 +1,30 @@
 // Copyright © 2016 Zellyn Hunter <zellyn@gmail.com>
 
 // marshal.go contains helpers for marshaling sector structs to/from
-// disk.
+// disk and block structs to/from devices.
 
 package disk
 
+import "io"
+
+// A ProDOS block.
+type Block [512]byte
+
+// BlockDevice is the interface used to read and write devices by
+// logical block number.
+type BlockDevice interface {
+	// ReadBlock reads a single block from the device. It always returns
+	// 512 byes.
+	ReadBlock(index uint16) (Block, error)
+	// WriteBlock writes a single block to a device. It expects exactly
+	// 512 bytes.
+	WriteBlock(index uint16, data Block) error
+	// Blocks returns the number of blocks on the device.
+	Blocks() uint16
+	// Write writes the device contents to the given Writer.
+	Write(io.Writer) (int, error)
+}
+
 // SectorSource is the interface for types that can marshal to sectors.
 type SectorSource interface {
 	// ToSector marshals the sector struct to exactly 256 bytes.
@@ -52,3 +72,44 @@ func MarshalLogicalSector(d LogicalSectorDisk, ss SectorSource) error {
 	}
 	return d.WriteLogicalSector(track, sector, bytes)
 }
+
+// BlockSource is the interface for types that can marshal to blocks.
+type BlockSource interface {
+	// ToBlock marshals the block struct to exactly 512 bytes.
+	ToBlock() (Block, error)
+	// GetBlock returns the index that a block struct was loaded from.
+	GetBlock() uint16
+}
+
+// BlockSink is the interface for types that can unmarshal from blocks.
+type BlockSink interface {
+	// FromBlock unmarshals the block struct from a Block. Input is
+	// expected to be exactly 512 bytes.
+	FromBlock(block Block) error
+	// SetBlock sets the index that a block struct was loaded from.
+	SetBlock(index uint16)
+}
+
+// UnmarshalBlock reads a block from a BlockDevice, and unmarshals it
+// into a BlockSink, setting its index.
+func UnmarshalBlock(d BlockDevice, bs BlockSink, index uint16) error {
+	block, err := d.ReadBlock(index)
+	if err != nil {
+		return err
+	}
+	if err := bs.FromBlock(block); err != nil {
+		return err
+	}
+	bs.SetBlock(index)
+	return nil
+}
+
+// MarshalBlock marshals a BlockSource to its block on a BlockDevice.
+func MarshalBlock(d BlockDevice, bs BlockSource) error {
+	index := bs.GetBlock()
+	block, err := bs.ToBlock()
+	if err != nil {
+		return err
+	}
+	return d.WriteBlock(index, block)
+}
diff --git a/lib/disk/ops.go b/lib/disk/ops.go
index 2e82b23..eac9704 100644
--- a/lib/disk/ops.go
+++ b/lib/disk/ops.go
@@ -9,6 +9,7 @@ package disk
 import (
 	"errors"
 	"fmt"
+	"io"
 	"sort"
 	"strings"
 )
@@ -42,6 +43,8 @@ type Operator interface {
 	// is false, it returns with an error. Otherwise it returns true if
 	// an existing file was overwritten.
 	PutFile(fileInfo FileInfo, overwrite bool) (existed bool, err error)
+	// Write writes the underlying disk to the given writer.
+	Write(io.Writer) (int, error)
 }
 
 // FileInfo represents a file descriptor plus the content.
@@ -51,40 +54,40 @@ type FileInfo struct {
 	StartAddress uint16
 }
 
-// operatorFactory is the type of functions that accept a SectorDisk,
+// diskOperatorFactory is the type of functions that accept a SectorDisk,
 // and may return an Operator interface to operate on it.
-type operatorFactory func(SectorDisk) (Operator, error)
+type diskOperatorFactory func(SectorDisk) (Operator, error)
 
-// operatorFactories is the map of currently-registered operator
-// factories.
-var operatorFactories map[string]operatorFactory
+// diskOperatorFactories is the map of currently-registered disk
+// operator factories.
+var diskOperatorFactories map[string]diskOperatorFactory
 
 func init() {
-	operatorFactories = make(map[string]operatorFactory)
+	diskOperatorFactories = make(map[string]diskOperatorFactory)
 }
 
-// RegisterOperatorFactory registers an operator factory with the
-// given name: a function that accepts a SectorDisk, and may return an
-// Operator. It doesn't lock operatorFactories: it is expected to be
-// called only from package `init` functions.
-func RegisterOperatorFactory(name string, factory operatorFactory) {
-	operatorFactories[name] = factory
+// RegisterDiskOperatorFactory registers a disk operator factory with
+// the given name: a function that accepts a SectorDisk, and may
+// return an Operator. It doesn't lock diskOperatorFactories: it is
+// expected to be called only from package `init` functions.
+func RegisterDiskOperatorFactory(name string, factory diskOperatorFactory) {
+	diskOperatorFactories[name] = factory
 }
 
-// OperatorFor returns an Operator for the given SectorDisk, if possible.
-func OperatorFor(sd SectorDisk) (Operator, error) {
-	if len(operatorFactories) == 0 {
+// OperatorForDisk returns an Operator for the given SectorDisk, if possible.
+func OperatorForDisk(sd SectorDisk) (Operator, error) {
+	if len(diskOperatorFactories) == 0 {
 		return nil, errors.New("Cannot find an operator matching the given disk image (none registered)")
 	}
-	for _, factory := range operatorFactories {
+	for _, factory := range diskOperatorFactories {
 		if operator, err := factory(sd); err == nil {
 			return operator, nil
 		}
 	}
-	names := make([]string, 0, len(operatorFactories))
-	for name := range operatorFactories {
+	names := make([]string, 0, len(diskOperatorFactories))
+	for name := range diskOperatorFactories {
 		names = append(names, `"`+name+`"`)
 	}
 	sort.Strings(names)
-	return nil, fmt.Errorf("Cannot find an operator matching the given disk image (tried %s)", strings.Join(names, ", "))
+	return nil, fmt.Errorf("Cannot find a disk operator matching the given disk image (tried %s)", strings.Join(names, ", "))
 }
diff --git a/lib/dos3/dos3.go b/lib/dos3/dos3.go
index 67293e6..a2fd121 100644
--- a/lib/dos3/dos3.go
+++ b/lib/dos3/dos3.go
@@ -7,6 +7,7 @@ package dos3
 import (
 	"encoding/binary"
 	"fmt"
+	"io"
 	"strings"
 
 	"github.com/zellyn/diskii/lib/disk"
@@ -669,6 +670,11 @@ func (o operator) PutFile(fileInfo disk.FileInfo, overwrite bool) (existed bool,
 	return false, fmt.Errorf("%s does not implement PutFile yet", operatorName)
 }
 
+// Write writes the underlying disk to the given writer.
+func (o operator) Write(w io.Writer) (int, error) {
+	return o.lsd.Write(w)
+}
+
 // operatorFactory is the factory that returns dos3 operators given
 // disk images.
 func operatorFactory(sd disk.SectorDisk) (disk.Operator, error) {
@@ -684,5 +690,5 @@ func operatorFactory(sd disk.SectorDisk) (disk.Operator, error) {
 }
 
 func init() {
-	disk.RegisterOperatorFactory(operatorName, operatorFactory)
+	disk.RegisterDiskOperatorFactory(operatorName, operatorFactory)
 }
diff --git a/lib/prodos/prodos.go b/lib/prodos/prodos.go
index 592956d..72caa51 100644
--- a/lib/prodos/prodos.go
+++ b/lib/prodos/prodos.go
@@ -8,30 +8,14 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+
+	"github.com/zellyn/diskii/lib/disk"
 )
 
-// A single ProDOS block.
-type Block [512]byte
-
-// BlockDevice is the interface used to read and write devices by
-// logical block number.
-type BlockDevice interface {
-	// ReadBlock reads a single block from the device. It always returns
-	// 512 byes.
-	ReadBlock(index uint16) (Block, error)
-	// WriteBlock writes a single block to a device. It expects exactly
-	// 512 bytes.
-	WriteBlock(index uint16, data Block) error
-	// Blocks returns the number of blocks on the device.
-	Blocks() uint16
-	// Write writes the device contents to the given Writer.
-	Write(io.Writer) (int, error)
-}
-
-type VolumeBitMap []Block
+type VolumeBitMap []disk.Block
 
 func NewVolumeBitMap(blocks uint16) VolumeBitMap {
-	vbm := VolumeBitMap(make([]Block, (blocks+(512*8)-1)/(512*8)))
+	vbm := VolumeBitMap(make([]disk.Block, (blocks+(512*8)-1)/(512*8)))
 	for b := 0; b < int(blocks); b++ {
 		vbm.MarkUnused(uint16(b))
 	}
@@ -69,9 +53,9 @@ func (vbm VolumeBitMap) IsFree(block uint16) bool {
 }
 
 // ReadVolumeBitMap
-func ReadVolumeBitMap(bd BlockDevice, startBlock uint16) (VolumeBitMap, error) {
+func ReadVolumeBitMap(bd disk.BlockDevice, startBlock uint16) (VolumeBitMap, error) {
 	blocks := bd.Blocks() / 4096
-	vbm := make([]Block, blocks)
+	vbm := make([]disk.Block, blocks)
 	for i := uint16(0); i < blocks; i++ {
 		block, err := bd.ReadBlock(startBlock + i)
 		if err != nil {
@@ -84,7 +68,7 @@ func ReadVolumeBitMap(bd BlockDevice, startBlock uint16) (VolumeBitMap, error) {
 
 // Write writes the Volume Bit Map to a block device, starting at the
 // given block.
-func (vbm VolumeBitMap) Write(bd BlockDevice, startBlock uint16) error {
+func (vbm VolumeBitMap) Write(bd disk.BlockDevice, startBlock uint16) error {
 	for i, block := range vbm {
 		if err := bd.WriteBlock(startBlock+uint16(i), block); err != nil {
 			return fmt.Errorf("cannot write block %d of Volume Bit Map: %v", err)
@@ -137,8 +121,8 @@ type VolumeDirectoryKeyBlock struct {
 }
 
 // ToBlock marshals the VolumeDirectoryKeyBlock to a Block of bytes.
-func (vdkb VolumeDirectoryKeyBlock) ToBlock() Block {
-	var block Block
+func (vdkb VolumeDirectoryKeyBlock) ToBlock() disk.Block {
+	var block disk.Block
 	binary.LittleEndian.PutUint16(block[0x0:0x2], vdkb.Prev)
 	binary.LittleEndian.PutUint16(block[0x2:0x4], vdkb.Next)
 	copyBytes(block[0x04:0x02b], vdkb.Header.toBytes())
@@ -150,7 +134,7 @@ func (vdkb VolumeDirectoryKeyBlock) ToBlock() Block {
 }
 
 // FromBlock unmarshals a Block of bytes into a VolumeDirectoryKeyBlock.
-func (vdkb *VolumeDirectoryKeyBlock) FromBlock(block Block) {
+func (vdkb *VolumeDirectoryKeyBlock) FromBlock(block disk.Block) {
 	vdkb.Prev = binary.LittleEndian.Uint16(block[0x0:0x2])
 	vdkb.Next = binary.LittleEndian.Uint16(block[0x2:0x4])
 	vdkb.Header.fromBytes(block[0x04:0x2b])
@@ -184,8 +168,8 @@ type VolumeDirectoryBlock struct {
 }
 
 // ToBlock marshals a VolumeDirectoryBlock to a Block of bytes.
-func (vdb VolumeDirectoryBlock) ToBlock() Block {
-	var block Block
+func (vdb VolumeDirectoryBlock) ToBlock() disk.Block {
+	var block disk.Block
 	binary.LittleEndian.PutUint16(block[0x0:0x2], vdb.Prev)
 	binary.LittleEndian.PutUint16(block[0x2:0x4], vdb.Next)
 	for i, desc := range vdb.Descriptors {
@@ -196,7 +180,7 @@ func (vdb VolumeDirectoryBlock) ToBlock() Block {
 }
 
 // FromBlock unmarshals a Block of bytes into a VolumeDirectoryBlock.
-func (vdb *VolumeDirectoryBlock) FromBlock(block Block) {
+func (vdb *VolumeDirectoryBlock) FromBlock(block disk.Block) {
 	vdb.Prev = binary.LittleEndian.Uint16(block[0x0:0x2])
 	vdb.Next = binary.LittleEndian.Uint16(block[0x2:0x4])
 	for i := range vdb.Descriptors {
@@ -360,7 +344,7 @@ func (fd FileDescriptor) Validate() (errors []error) {
 
 // An index block contains 256 16-bit block numbers, pointing to other
 // blocks. The LSBs are stored in the first half, MSBs in the second.
-type IndexBlock Block
+type IndexBlock disk.Block
 
 // Get the blockNum'th block number from an index block.
 func (i IndexBlock) Get(blockNum byte) uint16 {
@@ -384,8 +368,8 @@ type SubdirectoryKeyBlock struct {
 }
 
 // ToBlock marshals the SubdirectoryKeyBlock to a Block of bytes.
-func (skb SubdirectoryKeyBlock) ToBlock() Block {
-	var block Block
+func (skb SubdirectoryKeyBlock) ToBlock() disk.Block {
+	var block disk.Block
 	binary.LittleEndian.PutUint16(block[0x0:0x2], skb.Prev)
 	binary.LittleEndian.PutUint16(block[0x2:0x4], skb.Next)
 	copyBytes(block[0x04:0x02b], skb.Header.toBytes())
@@ -397,7 +381,7 @@ func (skb SubdirectoryKeyBlock) ToBlock() Block {
 }
 
 // FromBlock unmarshals a Block of bytes into a SubdirectoryKeyBlock.
-func (skb *SubdirectoryKeyBlock) FromBlock(block Block) {
+func (skb *SubdirectoryKeyBlock) FromBlock(block disk.Block) {
 	skb.Prev = binary.LittleEndian.Uint16(block[0x0:0x2])
 	skb.Next = binary.LittleEndian.Uint16(block[0x2:0x4])
 	skb.Header.fromBytes(block[0x04:0x2b])
@@ -431,8 +415,8 @@ type SubdirectoryBlock struct {
 }
 
 // ToBlock marshals a SubdirectoryBlock to a Block of bytes.
-func (sb SubdirectoryBlock) ToBlock() Block {
-	var block Block
+func (sb SubdirectoryBlock) ToBlock() disk.Block {
+	var block disk.Block
 	binary.LittleEndian.PutUint16(block[0x0:0x2], sb.Prev)
 	binary.LittleEndian.PutUint16(block[0x2:0x4], sb.Next)
 	for i, desc := range sb.Descriptors {
@@ -443,7 +427,7 @@ func (sb SubdirectoryBlock) ToBlock() Block {
 }
 
 // FromBlock unmarshals a Block of bytes into a SubdirectoryBlock.
-func (sb *SubdirectoryBlock) FromBlock(block Block) {
+func (sb *SubdirectoryBlock) FromBlock(block disk.Block) {
 	sb.Prev = binary.LittleEndian.Uint16(block[0x0:0x2])
 	sb.Next = binary.LittleEndian.Uint16(block[0x2:0x4])
 	for i := range sb.Descriptors {
@@ -543,3 +527,66 @@ func copyBytes(dst, src []byte) int {
 	}
 	return copy(dst, src)
 }
+
+// operator is a disk.Operator - an interface for performing
+// high-level operations on files and directories.
+type operator struct {
+	dev disk.BlockDevice
+}
+
+var _ disk.Operator = operator{}
+
+// operatorName is the keyword name for the operator that undestands
+// prodos disks/devices.
+const operatorName = "prodos"
+
+// Name returns the name of the operator.
+func (o operator) Name() string {
+	return operatorName
+}
+
+// HasSubdirs returns true if the underlying operating system on the
+// disk allows subdirectories.
+func (o operator) HasSubdirs() bool {
+	return true
+}
+
+// Catalog returns a catalog of disk entries. subdir should be empty
+// for operating systems that do not support subdirectories.
+func (o operator) Catalog(subdir string) ([]disk.Descriptor, error) {
+	return nil, fmt.Errorf("%s doesn't implement Catalog yet", operatorName)
+	/*
+		fds, _, err := ReadCatalog(o.dev)
+		if err != nil {
+			return nil, err
+		}
+		descs := make([]disk.Descriptor, 0, len(fds))
+		for _, fd := range fds {
+			descs = append(descs, fd.descriptor())
+		}
+		return descs, nil
+	*/
+}
+
+// GetFile retrieves a file by name.
+func (o operator) GetFile(filename string) (disk.FileInfo, error) {
+	return disk.FileInfo{}, fmt.Errorf("%s doesn't implement GetFile yet", operatorName)
+}
+
+// Delete deletes a file by name. It returns true if the file was
+// deleted, false if it didn't exist.
+func (o operator) Delete(filename string) (bool, error) {
+	return false, fmt.Errorf("%s doesn't implement Delete yet", operatorName)
+}
+
+// PutFile writes a file by name. If the file exists and overwrite
+// is false, it returns with an error. Otherwise it returns true if
+// an existing file was overwritten.
+func (o operator) PutFile(fileInfo disk.FileInfo, overwrite bool) (existed bool, err error) {
+	return false, fmt.Errorf("%s doesn't implement PutFile yet", operatorName)
+}
+
+// Write writes the underlying device blocks to the given writer.
+func (o operator) Write(w io.Writer) (int, error) {
+	return o.dev.Write(w)
+}
diff --git a/lib/prodos/prodos_test.go b/lib/prodos/prodos_test.go
index 3764416..a11e0c1 100644
--- a/lib/prodos/prodos_test.go
+++ b/lib/prodos/prodos_test.go
@@ -6,10 +6,11 @@ import (
 	"testing"
 
 	"github.com/kr/pretty"
+	"github.com/zellyn/diskii/lib/disk"
 )
 
-func randomBlock() Block {
-	var b1 Block
+func randomBlock() disk.Block {
+	var b1 disk.Block
 	rand.Read(b1[:])
 	return b1
 }
diff --git a/lib/supermon/supermon.go b/lib/supermon/supermon.go
index 226ebef..188c28d 100644
--- a/lib/supermon/supermon.go
+++ b/lib/supermon/supermon.go
@@ -7,6 +7,7 @@ package supermon
 import (
 	"encoding/binary"
 	"fmt"
+	"io"
 	"strconv"
 	"strings"
 
@@ -783,6 +784,11 @@ func (o Operator) PutFile(fileInfo disk.FileInfo, overwrite bool) (existed bool,
 	return existed, nil
 }
 
+// Write writes the underlying disk to the given writer.
+func (o Operator) Write(w io.Writer) (int, error) {
+	return o.SD.Write(w)
+}
+
 // operatorFactory is the factory that returns supermon operators
 // given disk images.
 func operatorFactory(sd disk.SectorDisk) (disk.Operator, error) {
@@ -805,5 +811,5 @@ func operatorFactory(sd disk.SectorDisk) (disk.Operator, error) {
 }
 
 func init() {
-	disk.RegisterOperatorFactory(operatorName, operatorFactory)
+	disk.RegisterDiskOperatorFactory(operatorName, operatorFactory)
 }
diff --git a/lib/supermon/supermon_test.go b/lib/supermon/supermon_test.go
index a4c0a97..dd0c2de 100644
--- a/lib/supermon/supermon_test.go
+++ b/lib/supermon/supermon_test.go
@@ -126,11 +126,11 @@ func TestReadSymbolTable(t *testing.T) {
 // TestGetFile tests the retrieval of a file's contents, using the
 // Operator interface.
 func TestGetFile(t *testing.T) {
-	sd, err := disk.Open(testDisk)
+	sd, err := disk.OpenDisk(testDisk)
 	if err != nil {
 		t.Fatal(err)
 	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.OperatorForDisk(sd)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -213,11 +213,11 @@ func TestReadWriteSymbolTable(t *testing.T) {
 // TestPutFile tests the creation of a file, using the Operator
 // interface.
 func TestPutFile(t *testing.T) {
-	sd, err := disk.Open(testDisk)
+	sd, err := disk.OpenDisk(testDisk)
 	if err != nil {
 		t.Fatal(err)
 	}
-	op, err := disk.OperatorFor(sd)
+	op, err := disk.OperatorForDisk(sd)
 	if err != nil {
 		t.Fatal(err)
 	}