diff --git a/src/pkg/Make.deps b/src/pkg/Make.deps
index 088708fba5..9144ad40d9 100644
--- a/src/pkg/Make.deps
+++ b/src/pkg/Make.deps
@@ -1,4 +1,4 @@
-archive/tar.install: bufio.install bytes.install io.install os.install strconv.install
+archive/tar.install: bytes.install io.install os.install strconv.install strings.install
 base64.install: bytes.install io.install os.install strconv.install
 bignum.install: fmt.install
 bufio.install: io.install os.install strconv.install utf8.install
diff --git a/src/pkg/archive/tar/Makefile b/src/pkg/archive/tar/Makefile
index 2689b30f6a..78734ef58a 100644
--- a/src/pkg/archive/tar/Makefile
+++ b/src/pkg/archive/tar/Makefile
@@ -36,7 +36,7 @@ O1=\
 	common.$O\
 
 O2=\
-	untar.$O\
+	reader.$O\
 	writer.$O\
 
 
@@ -48,7 +48,7 @@ a1: $(O1)
 	rm -f $(O1)
 
 a2: $(O2)
-	$(AR) grc _obj$D/tar.a untar.$O writer.$O
+	$(AR) grc _obj$D/tar.a reader.$O writer.$O
 	rm -f $(O2)
 
 
diff --git a/src/pkg/archive/tar/untar.go b/src/pkg/archive/tar/reader.go
similarity index 97%
rename from src/pkg/archive/tar/untar.go
rename to src/pkg/archive/tar/reader.go
index 87382d4f5c..7e8f617b00 100644
--- a/src/pkg/archive/tar/untar.go
+++ b/src/pkg/archive/tar/reader.go
@@ -6,7 +6,6 @@ package tar
 
 // TODO(dsymonds):
 //   - pax extensions
-//   - rename this file to reader.go
 
 import (
 	"archive/tar";
@@ -20,13 +19,13 @@ var (
 	HeaderError os.Error = os.ErrorString("invalid tar header");
 )
 
-// A tar archive consists of a sequence of files.
 // A Reader provides sequential access to the contents of a tar archive.
+// A tar archive consists of a sequence of files.
 // The Next method advances to the next file in the archive (including the first),
 // and then it can be treated as an io.Reader to access the file's data.
 //
 // Example:
-// 	tr := NewTarReader(r);
+// 	tr := tar.NewReader(r);
 // 	for {
 //		hdr, err := tr.Next();
 //		if err != nil {
@@ -36,7 +35,7 @@ var (
 //			// end of tar archive
 //			break
 //		}
-//		io.Copy(tr, somewhere);
+//		io.Copy(tr, data);
 // 	}
 type Reader struct {
 	r io.Reader;
@@ -48,7 +47,7 @@ type Reader struct {
 func (tr *Reader) skipUnread()
 func (tr *Reader) readHeader() *Header
 
-// NewReader creates a new Reader reading the given io.Reader.
+// NewReader creates a new Reader reading from r.
 func NewReader(r io.Reader) *Reader {
 	return &Reader{ r: r }
 }
diff --git a/src/pkg/archive/tar/untar_test.go b/src/pkg/archive/tar/reader_test.go
similarity index 100%
rename from src/pkg/archive/tar/untar_test.go
rename to src/pkg/archive/tar/reader_test.go
diff --git a/src/pkg/archive/tar/writer.go b/src/pkg/archive/tar/writer.go
index 57e9a4607c..fbb0031fc5 100644
--- a/src/pkg/archive/tar/writer.go
+++ b/src/pkg/archive/tar/writer.go
@@ -28,7 +28,7 @@ var (
 // writing at most hdr.Size bytes in total.
 //
 // Example:
-// 	tw := NewTarWriter(w);
+// 	tw := tar.NewWriter(w);
 //	hdr := new(Header);
 //	hdr.Size = length of data in bytes;
 //	// populate other hdr fields as desired
@@ -112,19 +112,19 @@ func (tw *Writer) WriteHeader(hdr *Header) os.Error {
 	// TODO(dsymonds): handle names longer than 100 chars
 	nr := bytes.Copy(s.next(100), strings.Bytes(hdr.Name));
 
-	tw.octal(s.next(8), hdr.Mode);
-	tw.octal(s.next(8), hdr.Uid);
-	tw.octal(s.next(8), hdr.Gid);
-	tw.octal(s.next(12), hdr.Size);
-	tw.octal(s.next(12), hdr.Mtime);
-	s.next(8);  // chksum
-	s.next(1)[0] = hdr.Typeflag;
-	s.next(100);  // linkname
-	bytes.Copy(s.next(8), strings.Bytes("ustar\x0000"));
-	tw.cString(s.next(32), hdr.Uname);
-	tw.cString(s.next(32), hdr.Gname);
-	tw.octal(s.next(8), hdr.Devmajor);
-	tw.octal(s.next(8), hdr.Devminor);
+	tw.octal(s.next(8), hdr.Mode);	// 100:108
+	tw.octal(s.next(8), hdr.Uid);	// 108:116
+	tw.octal(s.next(8), hdr.Gid);	// 116:124
+	tw.octal(s.next(12), hdr.Size);	// 124:136
+	tw.octal(s.next(12), hdr.Mtime);	// 136:148
+	s.next(8);  // chksum (148:156)
+	s.next(1)[0] = hdr.Typeflag;	// 156:157
+	s.next(100);  // linkname (157:257)
+	bytes.Copy(s.next(8), strings.Bytes("ustar\x0000"));	// 257:265
+	tw.cString(s.next(32), hdr.Uname);	// 265:297
+	tw.cString(s.next(32), hdr.Gname);	// 297:329
+	tw.octal(s.next(8), hdr.Devmajor);	// 329:337
+	tw.octal(s.next(8), hdr.Devminor);	// 337:345
 
 	// The chksum field is terminated by a NUL and a space.
 	// This is different from the other octal fields.
diff --git a/src/pkg/archive/tar/writer_test.go b/src/pkg/archive/tar/writer_test.go
index 202530a0f0..5ada36b530 100644
--- a/src/pkg/archive/tar/writer_test.go
+++ b/src/pkg/archive/tar/writer_test.go
@@ -62,30 +62,39 @@ var writerTests = []*writerTest{
 }
 
 // Render byte array in a two-character hexadecimal string, spaced for easy visual inspection.
-func bytestr(b []byte) string {
-	s := fmt.Sprintf("(%d bytes)\n", len(b));
+func bytestr(offset int, b []byte) string {
 	const rowLen = 32;
+	s := fmt.Sprintf("%04x ", offset);
 	for i, ch := range b {
-		if i % rowLen == 0 {
-			// start of line: hex offset
-			s += fmt.Sprintf("%04x", i);
-		}
 		switch {
 		case '0' <= ch && ch <= '9', 'A' <= ch && ch <= 'Z', 'a' <= ch && ch <= 'z':
 			s += fmt.Sprintf("  %c", ch);
 		default:
 			s += fmt.Sprintf(" %02x", ch);
 		}
-		if (i + 1) % rowLen == 0 {
-			// end of line
-			s += "\n";
-		} else if (i + 1) % (rowLen / 2) == 0 {
-			// extra space
-			s += " ";
-		}
 	}
-	if s[len(s)-1] != '\n' {
-		s += "\n"
+	return s
+}
+
+// Render a pseudo-diff between two blocks of bytes.
+func bytediff(a []byte, b []byte) string {
+	const rowLen = 32;
+	s := fmt.Sprintf("(%d bytes vs. %d bytes)\n", len(a), len(b));
+	for offset := 0; len(a) + len(b) > 0; offset += rowLen {
+		na, nb := rowLen, rowLen;
+		if na > len(a) {
+			na = len(a);
+		}
+		if nb > len(b) {
+			nb = len(b);
+		}
+		sa := bytestr(offset, a[0:na]);
+		sb := bytestr(offset, b[0:nb]);
+		if sa != sb {
+			s += fmt.Sprintf("-%v\n+%v\n", sa, sb);
+		}
+		a = a[na:len(a)];
+		b = b[nb:len(b)];
 	}
 	return s
 }
@@ -115,8 +124,8 @@ testLoop:
 
 		actual := buf.Data();
 		if !bytes.Equal(expected, actual) {
-			t.Errorf("test %d: Incorrect result:\n%v\nwant:\n%v",
-				 i, bytestr(actual), bytestr(expected));
+			t.Errorf("test %d: Incorrect result: (-=expected, +=actual)\n%v",
+			         i, bytediff(expected, actual));
 		}
 	}
 }