P R O D R I V E L P S 2 7 0 S QUANTUM Native| Translation ------+-----+-----+----- Form 3.5"/SLIMLINE Cylinders 2740| | | Capacity form/unform 270/ MB Heads 2| | | Seek time / track 12.0/ 4.0 ms Sector/track | | | Controller SCSI2 SINGLE-ENDED Precompensation Cache/Buffer 128 KB LOOK-AHEAD Landing Zone Data transfer rate 4.000 MB/S int Bytes/Sector 512 10.000 MB/S ext SYNC Recording method RLL 1/7 operating | non-operating -------------+-------------- Supply voltage 5/12 V Temperature *C 55 | -40 65 Power: sleep W Humidity % 5 85 | 5 95 standby 0.8 W Altitude km -0.200 3.000| -0.200 12.000 idle 3.6 W Shock g 10 | 60 seek 5.7 W Rotation RPM 4500 read/write 5.0 W Acoustic dBA 33 spin-up 13.2 W ECC Bit 112,REED SOLOMON MTBF h 150000 Warranty Month Lift/Lock/Park YES Certificates CSA,FCC,TUV,UL1950,VDE ********************************************************************** L A Y O U T ********************************************************************** QUANTUM PRODRIVE LPS 270/540S PRODUCT MANUAL 81-104075-01 AUG. 1993 +--------+-------------------------------------------------+ | | A0 A1 A2 | | | JP2 +-+-+-++-+-+-+ ++ |XXJ1 | | +-+-+-++-+-+-+JP1 || |XX ++ | PO || |XXI |+------++-+ SCSI || |XXN | ++ | Terminator || |XXT | | J3 ++ |XXE | ++ | |.XR |+------++-+ ++ |XXF ++ | || |XXA | |+-+J5 SCSI || |XXC | +-|| |Control Terminator || |XXE | | |+-+Connector || |XX | | | ++ |XX | | | | | +-|+-+J2 |XX Power | | |+-+LED |XX +------+-+-------------------------------------------------+ | | | | | | | +---J5----+ +-J2+ |O O O O O| |O O|LED Connector --+---------+-+---+----------------PCB-- Side View | | | | + GND | | | +-- A2 | | +---- A1 | +------ A0 +-------- RESERVED ********************************************************************** J U M P E R S ********************************************************************** QUANTUM PRODRIVE LPS 270/540S PRODUCT MANUAL 81-104075-01 AUG. 1993 Jumper Setting ============== x = Factory default Jumper Options -------------- The configuration of three jumpers controls the drive's mode of operation: - A2, A1, A0 - SCSI Bus Identification Jumpers - PO - Product Option In addition to the hardware jumpers listed above, the ProDrive LPS 270/540S hard disk drive supports software control SCSI ID, Parity Enable, Wait Spin, and Self-Seek as determined by Mode Page 39h. The factory default is for the SCSI ID to be controlled by hardware jumper A2, A1, and A0 of JP1, SCSI bus parity checking to be controlled by hardware jumper PO, and the Wait/Spin option disabled. If the PO jumper is removed, SCSI bus parity checking is disabled. SCSI-Bus Device Identification Jumpers -------------------------------------- Used in combination, the jumper settings across pins A2, A1, and A0 determine the ProDrive LPS 270/540S hard disk drive's SCSI-bus device identification (SCSI ID). By default, Quantum configures the drive with a SCSI ID of six; that is, with jumpers installed across the pins labeled A2 and A1, and no jumper installed across the pins labeled A0. +----------+-----------------------+ | SCSI ID | Jumpers | | | A2 | A1 | A0 | +----------+-------+-------+-------+ | 0 | OPEN | OPEN | OPEN | | 1 | OPEN | OPEN | CLOSED| | 2 | OPEN | CLOSED| OPEN | | 3 | OPEN | CLOSED| CLOSED| | 4 | CLOSED| OPEN | OPEN | | 5 | CLOSED| OPEN | CLOSED| |x 6 | CLOSED| CLOSED| OPEN | | 7 | CLOSED| CLOSED| CLOSED| +----------+-------+-------+-------+ The SCSI bus supports up to eight devices, including the host system. A device's identification number determines its priority and must be unique in the system. Product Option (PO) Jumper -------------------------- The function of the PO jumper is determined by Mode Page 39. With the PO jumper installed, one of the following functions can be controlled: - Wait Spin - Enable Parity - Self Seek The default setting is that the PO jumper is installed and contolling the Enable Parity function, which checks parity on the SCSI bus. Wait/Spin (WS) Function ----------------------- At a power on or reset, with the Wait/Spin option disabled, the motor start to spin automatically, and the drive will become ready to perform read or write operations without the need for a start command. At a power on or reset, with the Wait/Spin option enabled, the host must send a START/STOP UNIT command to activate the drive motor. The Wait/Spin option permits power sequencing, to prevent an overload of the host's power supply due to simultaneous, peak start-up current demands from multiple devices. Once the drive receives a START/STOP UNIT command, it will become ready to perform read or write operations. A delayed startup without the need for a START command may also be enabled as determined by Mode Page 39h. Enable Parity (EP) Function --------------------------- The Enable Parity (EP) option controls parity checking of data across the SCSI bus. With parity checking enable (PO installed), the drive performs parity checking. With parity checking disabled (PO removed), the drive continues to generate parity information, but does not perform parity checking. Self-Seek (SS) Function ----------------------- Self-Seek can be initiated by the PO jumper in conjunction with Mode Page 39h, or the host can initiate a Self-Seek test by issuing a SEND DIAGNOSTIC command, with the self-test bit set to one. When power is applied to the drive with the Self-Seek test enabled, the drive initiates a Self-Seek test. The SCSI-bus device identifica- tion (SCSI ID) currently selected determined the Self-Seek test performed. For information about selecting a SCSI ID see the section "SCSI-Bus Device Identification Jumpers". With the SCSI ID set to six, its default value, the drive performs random seeks, verifying the cylinder ID after every seek. The random seeks continue as long as power is applied to the drive or until the drive encounters a seek error. If the SCSI ID is set to any value other than six, the drive executes seeks in a butterfly pattern. Each butterfly seek pattern: 1. Start at cylinder zero. 2. Seeks to the last data cylinder. 3. Performs successive seeks over a progressively narrower range of cylinders - incrementing by three at the lower limit of the range and decrementing by three at the upper limit of the range - until the drive seeks to the middle cylinder. 4. Performs successive seeks over a progressively wider range of cylinders - decrementing by three at the lower limit of the range and incrementing by three at the upper limit of the range. 5. Ends with a seek to cylinder zero. Seek in this butterfly pattern continue as long as is applied to the drive or until the drive encounters a seek error. During the Self-Seek test, the drive can execute any command. Quantum-Unique Drive Control Parameters, Page Code 39H ------------------------------------------------------ +--------+------+-----+-----+-----+-----+-----+-----+-----+ | |Bit 7 |Bit 6|Bit 5|Bit 4|Bit 3|Bit 2|Bit 1|Bit 0| +--------+------+-----+-----+-----+-----+-----+-----+-----+ |Byte 0 |RESERVED = 0| PAGE CODE = 39H | +--------+------------+-----------------------------------+ |Byte 1 | PAGE LENGTH = 06H | +--------+-----+------+-----+-----+-----+-----+-----+-----+ |Byte 2 |DIO |DII |FDB |RUEE |FDPE |R = 0|DUA |DRT | +--------+-----+------+-----+-----+-----+-----+-----+-----+ |Byte 3 |DDIS |DELDIS|RES=0|DPC |SSID | SCSIADR | +--------+-----+------+-----+-----+-----+-----+-----+-----+ |Byte 4 |PODIS|POSS |POEP |POWS |MDLY |SS |RES=0|WS | +--------+-----+------+-----+-----+-----+-----+-----+-----+ |Byte 5 | MOTOR DELAY TIME | +--------+------------------------------------------------+ |Byte 6-7| RESERVED = 0 | +--------+------------------------------------------------+ DIO - Disable Identify out (Byte 2, Bit 7) ------------------------------------------ When DIO is set to one, the drive does not require an IDENTIFY message from the initiator to disconnect and reconnect. When DIO is set to zero, the drive requires to send an IDENTIFY message prior to disconnecting. The default is zero. DII - Disable Identify IN (Byte 2, Bit 6) ----------------------------------------- When DII is set to one, the drive does not send an IDENTIFY message after reconnecting to an initiator. When DII is set to zero, the drive sends an IDENTIFY message after reconnecting. The default is zero. FDB - Fast Deassertion of Busy (Byte 2, Bit 5) ---------------------------------------------- This parameter is neither used nor required by applications using the drive. It is ignored. The default value is zero. RUEE - Reallocate Uncorrectable Error Enable (Byte 2, Bit 4) ------------------------------------------------------------ When RUEE is set to one and the ARRE bit in page 1 of the error- recovery parameters is set, the drive automatically writes data containing uncorrectable, hard errors to a different logical block and appends a new ECC that is correct for the data. Reading the new block would result in a MEDIUM ERROR - Reallocated Uncorrectable Data Read, with the sense key set to three and the sense code to AAH. Any write to the new block will clear this condition. When RUEE is set to zero and the drive determines that a hard error is encountered is uncorrectable, the drive will not attempt automatic reallocation. A CHECK CONDITION status, with a sense key of MEDIUM ERROR - Uncorrectable Data Error will result. The default is zero. FDPE - Fill Data Pattern Enabled (Byte 2, Bit 3) ------------------------------------------------ When FDPE is set to one, the drive will write the data pattern specified in byte 2 of the FORMAT UNIT command into every user- accesible sector on the drive when it exectes a FORMAT UNIT command. When FDPE is set to zero, the drive will ignore the information in byte 2 for the FORMAT UNIT command. Issuing a FORMAT UNIT command typically causes loss of data, even if FDPE is set to zero. Users should back up their data prior to formatting. The default is zero. R - RESERVED ------------ Bit 2 of byte 2 is reserved and must be set to zero. DUA - Disable Unit Attention ---------------------------- When DUA is set to one, the drive will not issue a CHECK CONDITION status with the UNIT ATTENTION sense key on the first command follow- ing a reset. The drive will execute the first command issued after a reset condition. When DUA is set to zero, a UNIT ATTENTION condition will exist following a power on, or a reset caused by either a BUS DEVICE RESET message or a hard RESET condition. The default is zero. DRT - Disable Reselection Timeout (Byte 2, Bit 0) ------------------------------------------------- When DRT is set to one, the drive will not time out during a reselection request. When DRT is set to zero and there is no BSY response from the initiator after a selection time-out period - 250 milliseconds - the drive will clear the bus. The default is zero. DDIS - Disable Disconnection (Byte 3, Bit 7) -------------------------------------------- Setting DDIS to on eprevents disconnection and reconnection during data transfer - either a read or write. The initial disconnection due to the implied seek during the execution of a READ command is not prevented, but no other disconnect will occur. On a WRITE command, the drive will disconnect after transfetting all data to the buffer. When DDIS is set to zero, disconnection is not suppressed. The default is zero. DELDIS - Delay of Disconnection (Byte 3, Bit 6) ----------------------------------------------- This parameter is neither used nor required by applications using the drive. It is ignored. The default is zero. R - RESERVED ------------ Bit 5 of byte 3 is reserved and must be set to zero. DPC - Disable Parity Control (Byte 3, Bit 4) -------------------------------------------- When set to zero, DPC controls parity checking of data across the SCSI bus. Setting DPC to one disables parity checking (the drive still generates parity, but does not perform parity checking). The default is zero. SSID - Software Selectable ID (Byte 3, Bit 3) --------------------------------------------- When SSID is set to zero, the jumper settings on the drive PCB determine the drive's SCSI ID at all times. When SSID is set to one, the SCSIADR bits (bits 0-2 of byte 3) determine the drive's SCSI ID and the jumper settings will be ignored. When the SSID bit is set to one, the SCSI ID will remain unchanged until the next reset or power power on. If at initial power on, the SSID bit is set to one - that is, if this bit's previous setting was saved on the disk - the SCSIADR bits will determine the drive's SCSI ID. Otherwise, the jumper settings on the drive PCB will determine its SCSI ID. The default is zero. SCSIADR - SCSI Address (Byte 3, Bits 2-0) ----------------------------------------- If SSID (Bit 3 of byte 3) is set to one, SCSIADR determines the drive's SCSI ID. If SSID is set to zero, the jumper settings on the drive PCB determine its SCSI ID. The description of SSID above. The default is zero. PODIS - Product Option Jumper Enable (Byte 4, Bit 7) ---------------------------------------------------- When PODIS is set to one, the PO jumper on the drive is allowed to control the drive fnctions specified by various bits in this byte (byte 4) of Mode Page 39h. When PODIS is set to zero, the PO jumper has no control over the drive functions specified in this byte. The default is one. POSS - Product Option Jumper Self-Seek Control (Byte 4, Bit 6) -------------------------------------------------------------- When POSS is set to one, the PODIS bit is set to one, the SS bit in this byte is set to one, and the PO jumper is installed, the drive performs self-seek. If either POSS or PODIS are set to zero or the SS bit is set to zero, or the PO jumper is not installed, the drive does not perform self-seek. The default is zero. POEP - Product Option Enable Parity Control (Byte 4, Bit 5) ----------------------------------------------------------- When POEP is set to one, the PODIS bit is set to one, the DPC bit is set to zero, and the PO jumper is installed, the drive performs parity checking across the SCSI bus. If POEP or PODIS are set to zero, or if the DPC bit is set to one or the PO jumper is not installed, the drive continues to generate parity information, but does not perform parity checking. The default is one. POWS - Product Option Jumper Wait Spin Control (Byte 4, Bit 4) -------------------------------------------------------------- When POWS is set to one, the POWS is set to one, the PODIS bit is set to one, the WS bit is set to one, and the PO jumper is installed, the drive performs Wait/Spins. If POWS or PODIS are set to zero, or if the WS bit is set to zero or the PO jumper is not installed, the drive does not perform Wait/Spin. The default is zero. MTDLY - Motor Delay Soft Jumper (Byte 4, Bit 3) ----------------------------------------------- When MTDLY is set to one, the drive delays the motor start by the amount specified in the MOTOR DELAY TIME byte of this mode page. When the bit is set to zero, no motor delay is implemented. The default is zero. SS - Self-Seek Soft Jumper (Byte 4, Bit 2) ------------------------------------------ Please refer to POSS description. The default is zero. R - RESERVED ------------ Bit 1 of byte 4 is reserved and must be set to zero. WS - Wait/Spin Soft Jumper (Byte 4, Bit 0) ------------------------------------------ Please refer to POWS description. The default is zero. Motor Delay Time - (Byte 5) --------------------------- The value stored in this byte specifies the motor delay time in 10 millisecond increments. The LSB (bit 0) is equal to 10 milliseconds. ********************************************************************** I N S T A L L ********************************************************************** QUANTUM PRODRIVE LPS 270/540S PRODUCT MANUAL 81-104075-01 AUG. 1993 Notes on Installation ===================== Installation direction ---------------------- horizontally vertically +-----------------+ +--+ +--+ | | | +-----+ +-----+ | | | | | | | | | +-+-----------------+-+ | | | | | | +---------------------+ | | | | | | | | | | | | | | | | | | +---------------------+ | +-----+ +-----+ | +-+-----------------+-+ +--+ +--+ | | | | +-----------------+ Orientation ----------- The mounting holes on the ProDrive LPS 270/540S hard disk drive allow the drive to be mounted in any orientation. Mounting -------- For mounting, #6-32 UNC screws are recommended. CAUTION: The PCB is very close to the mounting holes. Do not exceed the specified length for the mounting screws. The specified screw length allows full use of the mounting-hole threads, while avoiding damaging or placing unwanted stress on the PCB. To avoid stripping the mounting-hole threads, the maximum torque applied to the screws must not exceed 8 inch-pounds. Clearance --------- Clearance from the drive - except mounting surfaces - to any other surface must be 0.05 inches minimum. Ventilation ----------- The LPS 270/540S hard disk drive operates without a cooling fan, provided the ambient air temperature does not exceed 131*F (55*C). Power Sequencing ---------------- You may apply the power in any order or manner, or short or open either the power or power-return line with no loss of data or damage to the disk drive. However, data may be lost in the sector being written at the time of power loss. The drive can withstand transient voltages of +10% to -100% from nominal while powering up or down. Disk Caching ------------ The ProDrive LPS 270/540S hard disk drive incorporates DisCache a 96K disk cache, to enhance drive performance. This integrated feature can significantly improve system throughput. Read and write caching can be enabled or disabled using the SET CONFIGURATION command. Acoustics --------- +-----------------+-----------------------+----------+ | Operating Mode | Measured Noise | Distance | +-----------------+-----------------------+----------+ | Idle On Track | 33 dBA pressure level | 1 m | | typical | 4.0 Bels (sound power)| 39.3 in. | +-----------------+-----------------------+----------+ | Idle On Track | 36 dBA pressure level | 39.3 in | | maximum | 4.2 Bels (sound power)| (1 m) | +-----------------+-----------------------+----------+ Automatic Actuator Lock ----------------------- To ensure data integrity and prevent damage during shipment, the drive uses a dedicated landing zone and Quantum's patented AIRLOCK. The AIRLOCK holds the headstack in the landing zone whenever the disks are not rotating. It consists of an air vane mounted near the perimeter of the disk stack and a locking arm that restrains the actuator arm assembly. When DC power is applied to the motor and the disk stack rotates, the rotation generates an airflow on the surface of the disk. As the flow of air across the air vane increases with disk rotation, the locking arm pivots away from the actuator arm, enabling the headstack to move out of the landing. When DC power is removed from the motor, an electric return mechanism automatically pulls the actuator into the landing zone, where the AIRLOCK holds it in place. Connectors ---------- J1 is a two section combination connector. The drive's DC power is applied to section A. The SCSI interface (50-pin) uses section B. The connector is mounted on the back edge of the printed-circuit (PCB). +----------------------------------------+ | | | | | +-----J1--Section-B----------Section-A | | |+-------------------------++4-3-2-1+| | | ||oooooooooooooooooooooooo1||O O O O|| | | ||ooooooooooooooooooooooooo|| || | | |+-------------------------++-------+| | +-+------------------------------------+-+ Recommended header connector and strain relief: 50-pin connector base part AMP P/N 1-746195-2 or equivalent 50-pin connector strain relief AMP P/N 499508-2 or equivalent Recommended mating connector and their part numbers: 4-pin connector (J11 section A) AMP P/N 1-480424-0 or equivalent Loose-piece contacts AMP P/N VS 60619-4 or equivalent Strip contacts AMP P/N VS 61117-4 or equivalent -------------------+ --+ +------------+| pin 1 +12 VDC 1| | 4 3 2 1 || pin 2 +12 Volts Return -+ +------------+| pin 3 + 5 Volts Return ------------------+ pin 4 + 5 VDC LED Connector (J2) ------------------ The LED connector my be used to connect an external LED for the pur- pose of monitoring drive activity. A 220-ohm resistor is connected in series from the +LED pin to +5 volts. The -LED pin is connected to a switching transistor on the drive that turns on and lights the LED when the disk is performing a read or write operation. When no read or write operation is taking place, the transistor turns off and the LED is extinguished. +---------------------+--------------------------------+ | J2 Pins | Mating Connectir Type and Part | |Pin Number| Function | Number (or equivalent) | +----------+----------+--------------------------------+ | 1 | -LED | Two-position housing: | +----------+----------+ Molex P/N 51021-0200 | | 2 | +LED | Loose-piece contacts: | | | | Molex P/N 50058-8100 | +----------+----------+--------------------------------+ J5 Control Connector -------------------- J5 may be used to connect an external switch for setting the SCSI ID of the drive. The recommended mating connectors are: +---+-------------+----------------------------+ |Pin|Function | Mating Connector Type and | | | | Part Number (or equivalent)| +---+-------------+----------------------------+ | 1 |Ground | Five position housing: | | 2 |A2 | Molex P/N 51021-0500 | | 3 |A1 | Loose-piece contacts: | | 4 |A0 | Molex P/N 50058-8100 | | 5 |RESERVED (no | | | |connection) | | +---+-------------+----------------------------+ DC Motor Assembly ----------------- Integral with the base casting, the DC motor assembly is a fixed- shaft, brushless DC spindle motor that drives the counter-clockwise rotation of the disks. Air Filtration -------------- The ProDrive LPS hard disk drives are Winchester-type drives. The heads fly very close to the media surface. Therefore, it is essential that the air circulating within the drive be kept free of particles. Quantum assembles the drive in a Class-100, purified air environment, then seals the drive with a metal cover. When the drive is in use, the rotation of the disks forces the air inside of the drive through an internal filter. ********************************************************************** F E A T U R E S ********************************************************************** QUANTUM PRODRIVE LPS 270/540S PRODUCT MANUAL 81-104075-01 AUG. 1993 Product Overview ---------------- Quantum's ProDrive LPS 270/540S hard disk drives are a part of a family of high-performance, 1-inch-high, hard disk drives manufactured to meet the highest product quality standards. ProDrive LPS hard disk drives use nonremovable, 3 -inch hard disks. The ProDrive LPS 270/540S hard disk drives feature an embedded SCSI drive controller and use SCSI commands to optimize system performance. Because the drive manages media defects and error recovery internally, these operations are fully transparent to the user. The innovative design of ProDrive LPS 270/540S hard disk drives enables Quantum to produce a family of low-cost, high-reliability drives. Performance: Average rotational latency of 6.7 ms 128K buffer with 96K dynamic segmentation cache. Look-ahead DisCache feature with continues prefetch and WriteCache write-buffering capabilities. Read-on-arrival ECC-on-the-fly 1:1 interleave on read/write operations SCSI-bus active termination SCSI-bus active negation drivers Formatted Capacity ------------------ At the factory, the ProDrive LPS 270/540S receives a low-level format that creates the actual tracks and sectors on the drive. Reliability ----------- Mean Time Between Failures (MTBF): 150,000 Power On Hours (POH), typical usage The Quantum MTBF numbers represent Bell-Core MTBF TR-TSY-000332 predictions and represent the minimum MTBF that Quantum or a customer would expect from the drive. The projected field MTBF is 300,000 hours. Preventive Maintenance (PM): Not required Start/Stop: 20,000 cycles (minimum) Component Life: 5 Years Error Detection and Correction ------------------------------ As disk drive areal densities increase, obtaining extremely low error rates requires a new generation of sophisticated error-correction codes. Quantum ProDrive LPS 270/540S series hard disk drives implement 112-bit single and double burst Reed-Solomon error- correction techniques to reduce the uncorrectable read error rate to less than one bit in 1 x 10(14) bits read. When errors occurs, an automatic retry and a more rigorous double- burst correction algorithm enable the correction of any sector with two bursts of three incorrect bytes each or up to six multiple random one-byte burst errors. In addition to these advanced error correction capabilities, the drive's additional cross-checking code and algorithm double checks the main ECC correction to greatly re- duce the probability of miscorrection. Defect Management ----------------- The ProDrive LPS 270/540S allocates one sector per two tracks as a spare. In the factory, the media is scanned for defects. If a sector on a cylinder is found to be defective, the address of the sector is added to the drive's defect list. Sectors located physically subsequent to the defective sector are assigned logical block addresses such that a sequential ordering of logical blocks results. This inline sparing technique is employed in an attempt to eliminate slow data transfer that would result from a single defective sector on a cylinder in a ProDrive LPS 270S hard disk drive and two defective sectors on a cylinder in a ProDrive LPS 540S hard disk drive. If more than one sector is found defective on a cylinder, the inline sparing technique is applied only to the first sector. The remaining defective sectors are replaced with the nearest available spare sectors on nearby cylinders. Such an assignment of additional replacement sectors from nearby sectors rather than having a central pool of spare sectors is an attempt to minimize the motion of the actuator and head that otherwise would be needed to find a replace- ment sector. The result is minimal reduction of data throughput. Seek Time --------- +----------------------------------+--------+ | |270/540S| +----------------------------------+--------+ |Track-to-Track msec. typ. | 4 | +----------------------------------+--------+ |Average write msec. typ. | 13 | | msec. max. | 14 | +----------------------------------+--------+ |Full stroke msec. typ. | 23 | | msec. max. | 25 | +----------------------------------+--------+ Data Transfer Rates ------------------- Data is transferred from the disk to the read buffer at a rate up to 5.8 MB/s in bursts. Data is transferred from the read buffer to the SCSI bus at a rate of up to 6.0 MB/sec in the asynchronous mode, or at up to 10.0 MB/s in the synchronous mode. Track and Cylinder Skewing -------------------------- Track and cylinder skewing in the ProDrive LPS 270/540S minimizes latency time and thus increases data throughput. Track Skewing ------------- Track skewing reduces the latency time that results when the drive must switch read/write heads to access sequential data. A track skew is employed such that the next logical sector of data to be accessed will be under the read/write head once the head switch is made and the data is ready to be accessed. Thus, when sequential data is on the same cylinder but on a different disk surface, a head switch is needed but not a seek. Since the sequential head-switch time is well defined on the ProDrive LPS 270/540S, the sector addresses can be optimally positioned across track boundaries to minimize the latency time during a head switch. Cylinder Skewing ---------------- Cylinder Skewing also is used to minimize the latency tome associated with a single-cylinder seek. The next logical sector of data that crosses a cylinder boundary is positioned on the drive such that after a single-cylinder seek is performed, and when the drive is ready to continue accessing data, the sector to be accessed is positioned directly under the read/write head. Therefore, the cylinder skew takes place between the last sector of data on the last head of a cylinder and the first sector of data on the first head of the next cylinder. Since single-cylinder seeks are well defined on the ProDrive LPS 270/540S, the sector addresses can be optimally positioned across cylinder boundaries to minimize the latency time associate with a single-cylinder seek.