Full text of DOI:10.1109/40.865865

THE
MEMORY STICK
T
HE COMPACT
HOUSEHOLD ELECTRICAL DEVICES. IT STORES STILL IMAGES
VOICE AND MUSIC TOGETHER ON THE SAME MEDIA AND PROTECTS
COPYRIGHTED MATERIAL
M
EMORY
S
TICK RECORDING CARD CONNECTS VARIOUS
,
MOVING IMAGES
,
,
,
.
With rapidly falling semiconductor
memory costs, compact and removable mem-
ory cards are beginning to catch on. Most
memory cards, however, are primarily designed
as computer peripherals—they do not provide
ꢀ applies a unique copyright protection
technology called MagicGate to protect
copyrighted data.
This easy-to-use media connects a variety
the copyright protection that is essential in of electrical devices by allowing different types
handling copyrighted materials such as music. of application data to be stored in the same
As a result, an optimum media for audiovisu- media while maintaining data compatibility.
al appliances has not been available.
This article discusses future development
In response to this need, we developed the plans for the Memory Stick after first describing
Memory Stick, which consists of a controller its features for specific application products.
and memory. It
Specifications
ꢀ
ꢀ
is compact, light, of slim rectangular
shape, easy to carry and handle;
Figure 1 shows the external view of the
Memory Stick, Figure 2 shows its outer dimen-
Shigeo Araki
Sony Corporation
provides high reliability due to fewer con- sions, and Table 1 lists the specifications.
tact pins and a terminal structure that
prevents physical contact;
To reduce the number of connector pins,
the Memory Stick uses a serial interface instead
ꢀ
ꢀ
ꢀ
employs an erasure-prevention switch to of the parallel interface used in conventional
easily protect data; memory cards. As a result, using only 10 pins,
provides a built-in controller for adop- inclusive of the pins for future enhancements,
tion of most kinds of flash memories; realizes a smaller contact area. This makes the
offers easier communication with PCs Memory Stick smaller and slimmer at 50-mm
through its adoption of FAT for the file long, 21.5-mm wide, and 2.8-mm thick.
management system;
Because the Memory Stick is compact, com-
ꢀ
ensures compatibility between appliances patible products can also be designed smaller,
by specifying respective formats and offering more design flexibility.
directories for applications such as still
To ensure proper handling, a partition
images, moving pictures, voice, and between the Memory Stick’s terminals keeps
music; and
them from being touched; and every time the
40
0272-1732/00/$10.00  2000 IEEE

Stick is inserted and withdrawn, it cleans itself.
Our designers also added a notch on the
Memory Stick to ensure proper insertion of
the Stick and included an erasure-prevention
switch similar to those on videotape cassettes
and floppy disks.
The Memory Stick consists of a flash EE- Figure 1. Memory Stick external view.
PROM and a controller. Its unique protocol
for interfacing between devices allows the con-
Terminals
troller to be modified so present and future
flash EEPROMs can be adopted.
Erasure
21.5 mm
prevention switch
The Memory Stick also uses a copyright-
protection technique called MagicGate that
allows copyrighted material such as music to
be recorded. It is currently available in stor-
age capacities of 4, 8, 16, 32, and 64 Mbytes;
in the future 128-Mbyte capacities will be
available.
LOCK
System configuration
Figure 3 (next page) shows the internal
structure and system configuration of the
Memory Stick.
2.8 mm
The controller controls various flash EE-
PROMs, absorbs differences among flash Figure 2. Memory Stick dimensions (mm).
EEPROMs, corrects errors in accordance with
the characteristics of each flash EEPROM
error, and converts parallel data to serial data
Table 1. Memory Stick specifications.
and vice versa. Therefore if the controller is
designed by observing the serial interface pro-
tocol, any kind of flash EEPROM, existing or
upcoming, can be adopted for the memory.
The controller’s load is not large, so the impact
on cost is kept to a minimum.
Item
Description
4, 8, 16, 32, and 64 (currently); 128 (future)
10
Capacity (Mbytes)
No. of connector pins
Interface type
Serial clock
Serial
20 MHz (maximum)
The controller consists of six blocks: the ser-
ial interface, register, page buffer, flash inter-
face, attribute ROM, and OSC cont.
The serial interface defines the protocol to
transfer data with three signals, SCLK (serial
clock), BS (bus state), and SDIO (serial data
in/out). In addition, it checks communica-
tion errors with the cyclic redundancy code
Write speed
1.5 Mbytes/s (maximum)
2.45 Mbytes/s (maximum)
2.7 V to 3.6 V
Read speed
Power source voltage
Operating current
Dimensions
45 mA (average); 130 µΑ (standby)
21.5 mm wide × 50 mm long × 2.8 mm thick
~4 grams
Weight
(
CRC). The host appliance accesses the regis- tion necessary to manufacture and initially
ter group and page buffer using transmission- format the Memory Stick.
control protocol (TCP) commands. Because the serial interface works by receiv-
The flash interface transfers data between ing the SCLK signal from the host, and the
the page buffer and flash EEPROM based flash interface works by the clock of the con-
on the parameter value in the register group, troller, the host needs to supply only SCLK
and reads, writes, and erases the data. It gen- to communicate with the Memory Stick and
erates and checks error-correcting code can adopt any frequency up to 20 MHz. The
(
ECC), which is essential in dealing with a OSC cont controls the controller’s clock and
flash EEPROM. stops the clock in sleep mode to minimize
The attribute ROM includes the informa- power consumption.
JULY–AUGUST 2000
41

MEMORY STICK
Controller
Flash
Vss
BS
Vcc
5
12 bytes 16 bytes
Register
SDIO
Reserve
INS
5
12 bytes 16 bytes
Page
buffer
(512 bytes)
512 bytes 16 bytes
12 bytes 16 bytes
Serial
interface
Flash
interface
5
Reserve
SCLK
Vcc
ECC (3 bytes)
Attribute
ROM
Vss
512 bytes 16 bytes
12 bytes 16 bytes
5
OSC cont
512 bytes 16 bytes
Reset
Figure 3. System configuration.
host. The host always initiates
communication.
SDIO transfers data after
adding CRC based on 512-
byte units.
BS
BS0
BS1
TPC
BS2
BS3
BS0
SDIO
SCLK
RDY/BSY
Data
CRC
The BS signal differs from
the usual chip enable signal
that shows data is active. BS
indicates the timing of the start
of data transfer, switching data
types. Under BS control, the
same SDIO notifies hand-
shake (RDY/BSY) and inter-
ruption (INT) signals. BS
classifies the data on SDIO
into four states: one state (BS0)
with no packet communica-
tion, and the other three states
(
a)
BS
BS0
BS1
TPC
BS2
BS3
BS0
SDIO
SCLK
Data
CRC
RDY/BSY
(
b)
(BS1, BS2, and BS3) with
Figure 4. Timing example: read protocol (a) and write protocol (b).
packet communication, which
control the output timing of all
data on SDIO. Table 2 lists the
Serial interface
respective states. States BS1 to BS3 are consid-
We adopted the BS-controlled serial inter- ered as one packet, and each communication
face—which keeps the overhead involved in must be completed within a packet.
data transfer to a minimum—for interfaces
TPC commands transfer at BS1 and define
with the host. Figure 4 gives an example of the the type of transferred data and the correct
timing for the serial interface’s three signals. protocol for states BS2 and BS3. The signals
The host supplies SCLK and BS, and the on SDIO then transfer data and handshaking
SDIO is a half-duplex transfer from and to the based on the protocol.
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Table 2. Bus states in read and write protocols.
State
BS status
Description
BS0
Low
INT transfer state: A state in which packet communication is not done; used as a transmission line for INT
signals (interruption).
BS1
BS2
High
Low
TPC state: Packet starts and transfers TPC from host to Memory Stick.
Data transfer state for write protocol; transferring data to Memory Stick. Handshake state for read
protocol: Waiting for RDY signal.
BS3
High
Handshake state for write protocol: Waiting for RDY signal. Data transfer state for read protocol. Reading
data from Memory Stick.
When an error is generat-
ed in a packet communica-
tion, BS automatically
switches to a mode that alter-
nates between BS0 and BS1
to avoid bus collision on
SDIO.
Root
root
MEMSTICK.IND
DCIM
100MSDCF
DSC00001.JPG
For picture
DSC00002.JPG
Picture file
Directory name
Directory
File format and directory
management
For music
Hi-Fi
Voice
Since the Memory Stick is
mainly focused on audiovisu-
al devices handling still
images, moving images,
voice, and music, it is rarely
called on to handle small
data. To avoid complication
For voice
File name
File
For relation
Control
in file management, the min- Figure 5. Directory structure example.
imum unit for handling data
is 8 or 16 Kbytes.
For easy data transfer between audiovisual to enjoy audio and visuals by connecting PCs
devices and PCs, the Memory Stick adopts and audiovisual devices. For that purpose we
the FAT file management system generally defined an additional information format to
used on PCs.
link data handled on various audiovisual
Because we wanted the Memory Stick to devices to various application data. For
handle still images, moving images, voice, and instance, we enabled functions such as adding
music together on the same media, we defined voice recordings onto the still image recorded
the format of each application and predefined by a digital still camera.
the directory management for compatibility
Furthermore, the Memory Stick stores mul-
among the appliances (Figure 5). We adopt- tiple application data such as still images,
ed the DCF (the design rule for camera file movies, voice, and music. By predefining for-
systems) standard of JEIDA (Japan Electron- mat and directory management for each appli-
ic Industry Development Association), for cation, we ensured compatibility between
still-image formats.1
devices. (See Figure 5 again.)
ADPCM, the ITU-T Recommendation
G.726, supports voice formats. The com- MagicGate
pression rate is defined based on applications
With music changing from analog to digi-
for converting voice data to text data when tal, and the Internet growing rapidly, copy-
Memory Stick-carrying data recorded on a righting matter is becoming a serious
2
-4
voice recorder is inserted into a PC. Also, problem. To solve this problem, Memory
as stated earlier, we wanted to develop a way Stick adopts the MagicGate technology to
JULY–AUGUST 2000
43

MEMORY STICK
Controller
Flash
Vss
BS
Vcc
5
12 bytes 16 bytes
Register
SDIO
Reserve
INS
5
12 bytes 16 bytes
Page
buffer
(512 bytes)
512 bytes 16 bytes
12 bytes 16 bytes
Serial
interface
Flash
interface
5
Reserve
SCLK
Vcc
ECC (3 bytes)
Attribute
ROM
Vss
512 bytes 16 bytes
5
5
12 bytes 16 bytes
12 bytes 16 bytes
ENC/DEC
Key
OSC cont
Reset
Figure 6. MG Memory Stick system configuration. B = bytes
guard copyrighted data, en-
sure compatibility between
appliances, and refuse illegal-
ly produced appliances.
MG host
MG Memory Stick
ID is loaded into register.
Random number is
generated (Rms).
MagicGate consists of two
technologies: authentication
distinguishes whether the
device legally supports Mag-
icGate with a unique ID
number for each Memory
Stick, and encryption protects
Authentication number
is generated.
Challenge
Random number is generated (Rd).
Authentication code 1 is
generated (AUC1D).
Random number is generated (Sd).
5,6
the contents.
The MagicGate Memory
Stick (referred to as MG
Memory Stick hereafter) con-
troller adopts two additional
blocks—encryption circuit
and key—as shown in Figure
Authentication code 1 is
generated (AUC1M).
AUC1D = AUC1M?
Authentication code 2 is
generated (AUC2M).
Random number is
generated (Sms).
Response/challenge
6
.
The host encrypts the con-
tents of the recorded data,
while the MG Memory Stick
only encrypts the key. As a
result, the Memory Stick con-
troller has fewer tasks.
Authentication code is
generated (AUC2D).
AUC2D = AUC2M?
Authentication is completed.
Session key is generated (SeK).
Response
Authentication is completed.
Session key is generated (SeK).
Figure 7 shows the authen-
tication flow between the MG
Memory Stick and the host.
Figure 7. Flow for authentication control.
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MG host
MG Memory Stick
CK (contents key) generation
encryption with session key
E(SeK,CK)
D(Sek,E(Sek,CK))→CK
Decryption with session key
Encryption with storage key
E(Kstm,CK)
Write to flash memory
after formatting
E(Kstm,CK)
(
a)
E(CK, Contents)
MG host
MG Memory Stick
E(Kstm,CK)
E(CK, Contents)
Read flash memory
Key extraction
D(Kstm,E(Kstm,CK))→CK
Decryption with storage key
Encryption with session key
E(Sek,CK)
Decryption wtih session key
D(Sek,E(Sek,CK))→CK
(
b)
Figure 8. Key encryption recording flow (a) and playback flow (b).
The host and the MG Memory Stick iden- Data playback
tify each other by a three-pass authentication
The host reads the contents encrypted by
technique, using the MG Memory Stick’s CK and the CK contents encrypted by Kstm
unique ID number. After authentication, SeK from the MG Memory Stick’s flash EEPROM
(the common session key) is generated, allow- and sends the CK to the MG Memory Stick
ing the contents to be recorded and played without decryption.
back with the SeK.
The MG Memory Stick decrypts the CK
Figure 8 shows the flow for the contents of with Kstm, then again encrypts the CK with
the recording and playback to and from the SeK, and sends the data back to the host.
MG Memory Stick, and the key transforma-
tion procedure.
Finally, the host decrypts the CK with SeK
and then decrypts the contents with the CK
to playback.
Data recording
By these technologies, only the MG Mem-
The host encrypts CK (the contents key by ory Stick and the devices that have adopted
which contents is encrypted) with SeK and MagicGate legally are able to authenticate
sends it to the MG Memory Stick.
and decrypt data. This method protects the
The MG Memory Stick decrypts CK with copyright.
SeK and again encrypts CK using the MG
We are developing a new technology, Open-
Memory Stick’s unique Kstm (storage key), MG, for copyright protection when handling
then sends the data back to the host.
music contents on a PC. By combining Open-
Finally, the host records 1) the contents MG and the MagicGate technology, we turn
encrypted by CK and 2) the CK encrypted a new AV-IT environment—in which various
by Kstm to the MG Memory Stick’s flash AV appliances and PCs are connected through
EEPROM.
networks—into reality.
JULY–AUGUST 2000
45

MEMORY STICK
Application products and
future developments
images or moving pictures, electric books, and
movies with copyright protection to be dis-
Viewer
We first announced devel- tributed and exchanged through the networks.
opment of our Memory Stick MagicGate technology is adaptable to such
in July of 1997, and precisely a transactions and would be of increasing impor-
year later announced commer- tance in the future, not to mention the impor-
cial production. Two months tance of the MG Memory Stick media itself.
Memory Stick
Photography
Memory Stick
later, in September of 1998, we
introduced the Memory Stick and a new form of enjoyment have begun in the
to the market. In February world of still images, with compact, easy-to-use
Materialization of unprecedented functions
Print
(a)
1
999 we added the Memory AV appliances taking advantage of “mechanic-
Memory Stick
Memory Stick
Stick’s copyright protection fea- less”(no moving parts) features of recording
ture and launched it in Decem- media, and by connecting such products via the
ber of the same year.
The available compatible ucts (Memory Stick Walkman, VAIO PC) are
devices include digital still already being brought to the commercial stage.
cameras, digital video cameras,
Music download
Memory Stick. In the music area, some prod-
Walkman
Voice to text
We will continue to seek new opportuni-
and PCs as tools for the image ties and challenges to connect the respective
IC recorder processing tool, digital photo market via the Memory Stick.
MICRO
(b)
printers for outputting data,
and digital photo frames for
References
Memory Stick
displaying data. These provide
an environment in which
devices—mainly still images—
can be connected (Figure 9a).
Also, voice recorders and PC
application software for con-
verting data to text data (Fig-
ure 9b), and the Memory Stick
Walkman are available for
voice and music (Figure 9b).
1. DCF, Design rule for Camera File System,
Version 1.0, JEIDA-49-2-1998, JEIDA (Japan
Electronic Industry Development Assoc.),
http://www.jeida.or.jp/.
Programming
c)
Figure 9. The worlds of pictures (a),
audio/voice (b), and the AIBO robot (c).
2. CCITT Recommendation G.726 (12/90), ITU-
T, Int’l Telecommunication Union, Geneva,
http://www.itu.int/.
AIBO
(
3. ITU-T Appendix III (Rec. G.726), Appendix II
(Rec. G.727) (05/94), ITU-T, Int’l Telecom-
munication Union, http://www.itu.int/.
4. ITU-T Recommendation G.726—Annex A
(11/94), Int’l Telecommunication Union,
http://www.itu.int/.
The Walkman was launched at the same time as
the MagicGate Memory Stick.
AIBO, the entertainment robot, is a rather
unique application of the Memory Stick. Data
for controlling AIBO is created on a PC and
relayed to AIBO via the Memory Stick to
achieve the one and only AIBO (Figure 9c).
To realize much smaller devices, we are
developing Memory Stick Duo (tentative
name). It is more compact than the Memory
Stick, at 31-mm long, 20-mm wide, and 1.6-
5. ISO/IEC 9797, 2nd ed., 1994-04-15, Int’l
Organization for Standardization/Int’l Electro-
technical Commission, Geneva, http://www.
iso.ch and http://www.iec.ch/.
6. ISO/IEC 9798-4, 1st ed., 1995-03-15,
ISO/IEC, http://www.iso.ch and http://www.
iec.ch/.
mm thick. Memory Stick Duo will maintain Shigeo Araki is an assistant manager at Sony
compatibility with the Memory Stick. Corporation engaged in the development of the
We use multilevel technologies and flash Memory Stick. Prior to this, he was engaged in
EEPROMs to achieve larger capacity and the design and product management of
lower cost. In the near future, semiconductor SRAMs. Araki is an electronics graduate of the
memory cards will be able to record moving Engineering Department (Information Engi-
pictures. Realizing much higher performance neering) of the Yokohama National University.
will require the development of new tech-
nologies. In the 21st century, broadband net-
Direct any questions concerning this article
works will become the standard. They will to the author at Sony Corporation;
allow music and digital imaging such as still araki@cv.sony.co.jp.
46
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