Singer 40 - User Manual

The Singer Models 40 and 42 Disc Drives are high-speed, random-access storage devices designed as peripheral units for the System Ten computer. These drives connect to the central processor via a File Access Channel (FAC) and a Disc Controller, which consists of printed circuit cards within the central processor. An installation can include both models in any combination. Externally, the two models are identical, differing primarily in the type of disc pack used. Both models utilize removable disc packs.

The Model 40 Disc Drive uses a single disc pack, the Model 41 Disc Pack, which comprises six magnetic oxide-coated discs joined on a common vertical axis. These discs are approximately 14 inches in diameter, with about 0.4 inches between successive discs. The Model 41 Disc Pack has ten recording surfaces, with the top surface of the top disc and the bottom surface of the bottom disc not used for data recording. This pack offers a maximum data storage capacity of 10 million characters. The read/write head mechanism for the Model 40 has five arms, one for each interdisc gap. Each arm is equipped with two heads: one for the surface above the arm and one for the surface below. All five arms move in unison.

The Model 42 Disc Drive uses a pair of disc packs, mounted one on top of the other. Both packs must be mounted for the drive to operate. The bottom pack, known as the Model 41A Disc Pack, is referred to as the resident pack, while the top pack, the Model 41B Disc Pack, is the removable pack. Both packs can be removed by the operator. When mounted, they rotate together as a single unit. Each of the Model 41A and 41B Disc Packs consists of three magnetic oxide-coated discs joined on a common vertical axis, with dimensions similar to the Model 41. Each pack has four recording surfaces, and like the Model 41, the outermost surfaces are not used for recording. Each of these packs has a maximum data storage capacity of 4 million characters. The read/write head mechanism for the Model 42 has four arms, identical in appearance to the Model 40's mechanism, but with the middle arm (arm 2) missing.

On all three disc packs (Models 41, 41A, and 41B), each recording surface contains 200 concentric tracks, and each track is divided into 50 equal parts called sectors. Each sector stores 100 characters. Read or write operations always target a single sector.

The disc drives are independently powered and controlled via their own operator control panels. After mounting a disc pack (or pair of packs for the Model 42) and powering on the drive, the operator initiates pack rotation by moving the START/STOP switch to START. Once the pack reaches the operational speed of 2400 rpm ± 2%, the READY indicator light illuminates. The drive can operate in two states: local or on-line. In local mode, the drive is disconnected from the central processor. In on-line mode, it can perform read and write operations in response to instructions from the central processor. The ENABLE/DISABLE switch functions as a combined ON LINE and LOCAL switch. DISABLE places the drive in local mode, while ENABLE (with the READY light on) puts it on-line.

Key specifications for the Models 40 and 42 Disc Drives include:

• Dimensions: 30-1/4 inches (77 cm) width, 24 inches (61 cm) depth, 38 inches (97 cm) height.
• Minimum Service Clearances: 36 inches (91 cm) front and rear, 0 inches (0 cm) right and left.
• Approximate Weight (Floor): 321 lbs (146 kg) without a 10 lb (4.5 kg) disc pack.
• Maximum Heat Output/Hour: 3,9000 BTU (982.8 kcal).
• Electrical Requirements:
  • Voltage Range: 110-130V ± 10% or 208-230V ± 10%.
  • Frequency: 60 ± 1 Hz or 50 ± 1 Hz.
  • Current: 9.6A (110-130V) or 5.0A (208-230V).
  • Maximum Current Surge: 45A for 5 to 10 seconds (110-130V) or 25A for 5 to 10 seconds (208-230V).
  • Phases: Single.
  • KVA: 1.1.
• Operating Environment:
  • Temperature: 65 to 85°F (18 to 29.5°C).
  • Relative Humidity: 20 to 75%.
• Non-Operating (Storage) Environment:
  • Temperature: -30 to +150°F (-34 to +66°C).
  • Relative Humidity: 8 to 80%.

The operator control panel features three toggle switches and three indicator lights:

• POWER ON/POWER OFF Switch: Turns the drive power on and off.
• POWER Indicator Light: Illuminates when power is on.
• ENABLE/DISABLE Switch: When READY is on and this switch is ENABLE, the drive is on-line. In DISABLE, the drive is in local.
• START/STOP Switch: In START position, the pack rotates, brushes clean disc surfaces, and the head assembly positions at the outermost track. In STOP position, the head assembly retracts, and the pack halts.
• READY Indicator Light: On when the pack rotates at proper speed (2400 rpm ± 2%), provided no FILE UNSAFE condition exists.
• FILE UNSAFE Indicator Light: Turns on if a malfunction is detected that could cause data loss. It terminates current operations, prevents further instructions, and requires moving the START/STOP switch to STOP (and then back to START after the pack halts) to reset.

Instruction format for disc operations: Read and Write instructions addressing a disc drive require both the LA-field and LB-field to be zero. The A-field specifies a 100-location memory segment for input (Read) or output (Write). The B-field specifies a six-character memory segment containing the disc address. Both A-field and B-field can be modified by an index register.

The six-character disc address contains:

• Device number (0-9).
• Arm number (0-4; on Model 40, 0 is top arm; on Model 42, 0 is bottom arm).
• Track number (000-199; 000 is outermost track).
• Sector number (00-99; sectors 00-49 accessed by upper head, 50-99 by lower head). Only the numeric portions (bits 1-4) of each character are used for specifying this information. Bit 7 can be 0 or 1, but bit 5 must always be 1.

Write operations: A Write instruction writes 100 characters from memory to a sector. If the drive is off-line, the instruction terminates with Condition Codes 4 and 1 (Fault). The Models 40 and 42 perform an automatic "read after write" check. After writing, the sector is read and compared to the output area. If they match, the write is successful. If not, the operation is retried up to two more times. After three failed attempts, the sector is marked "bad," the operation terminates, and Condition Code 3 (Flag) is set. For Model 42, writing to a sector accessed by the non-existent middle arm (arm 2) terminates the instruction with Condition Code 3 (Flag). A FILE UNSAFE condition during a write terminates the operation with Condition Codes 4 and 1 (Fault). Write Control instructions are treated as Write instructions.

Read operations: A Read instruction reads 100 characters from a sector into main memory. If the drive is off-line, the instruction terminates with Condition Codes 4 and 1 (Fault). If a sector cannot be read successfully, it is retried up to three more times. After four failed attempts, the operation terminates with Condition Code 1 (Error). For Model 42, reading from a sector accessed by the non-existent middle arm (arm 2) terminates the instruction with Condition Code 3 (Flag). A FILE UNSAFE condition during a read terminates the operation with Condition Codes 4 and 1 (Fault). Track address verification is performed automatically. If a "bad" or uninitialized sector is attempted, the operation terminates with Condition Code 3 (Flag). If heads are positioned at the wrong track, the operation terminates with Condition Code 1 (Error), and heads reposition to track 000. Read Control instructions are treated as Read instructions.

Multi-partition considerations: A disc drive is "bound" to a partition when that partition initiates a "seek" (moving the read/write head mechanism to a track). It remains bound until the I/O operation is complete. While bound, no other partition can initiate a seek on that drive. In multi-drive installations, multiple seeks can occur simultaneously, but only one drive can transmit data at a time. The Disc Controller manages which drives are bound to which partitions. If a partition attempts to move the read/write head mechanism while transmitting data, it relinquishes control of the central processor and frees the disc drive. If an instruction addresses a drive bound to another partition, the executing partition relinquishes control until the drive is free. If an instruction addresses a free drive and requires a seek, the seek is initiated (binding the drive), and the partition relinquishes control until the seek is complete.

Timing considerations:

• Rotation Time: 25.0 ms.
• Arm Positioning Times: Minimum 2.5 ms (one track), Average 73.0 ms (track 000 to 099), Maximum 135.0 ms (track 000 to 199).
• Read Operation (after head positioning): 0.5 to 25.5 ms (includes 0-25 ms rotational delay and 0.5 ms read time). Each retry takes 25 ms.
• Write Operation (after head positioning): 26.5 to 51.5 ms (includes 0-25 ms rotational delay, 1 ms for Disc Controller timing algorithm, 0.5 ms write time, and 25 ms for read-after-write verification).
• Overlap Timings (maximum computation time between consecutive I/O instructions on the same track):
  • Read-Read: 1.6 ms.
  • Write-Read: 0.6 ms.
  • Write-Write: 1.6 ms.
  • Read-Write: 0.6 ms. (Note: The Disc Controller takes 1 ms for its timing algorithm at the start of a write, reducing available computation time for a second write instruction). The disc is formatted such that the fifth sector following a read/written sector is the next one that can be accessed without an additional revolution, making consecutive sector operations efficient.

Operating instructions for disc pack handling:

• Mounting a Model 41 Disc Pack (Model 40 Drive): Lift the carrying case by the handle. Turn the bottom knob counterclockwise to remove the case bottom. Place the pack on the spindle. Turn the top handle clockwise until it stops. Lift the case off.
• Mounting a Model 41A Disc Pack (Model 42 Drive, bottom pack): Lift the carrying case by the handle. Turn the bottom knob counterclockwise to remove the case bottom. Place the pack on the spindle. Lift the release knob on the top of the case and lift the case off.
• Mounting a Model 41B Disc Pack (Model 42 Drive, top pack): Lift the carrying case by the handle. Turn the bottom knob counterclockwise to remove the case bottom. Place the pack on top of the resident pack, aligning large arrows. Ensure the pin from the resident pack fits into the hole in the removable pack, turning slightly if needed to lock them. Press the top handle down and turn clockwise until it stops. Lift the case off.
• CAUTION: Model 41A and 41B Disc Packs are not interchangeable with Model 40 Disc Drives.
• Removing a Disc Pack (Model 41 from Model 40, or Model 41B from Model 42): Place the top of the carrying case on the pack. Turn the top handle counterclockwise. Lift the case off when the pack turns freely. Hold the pack upside down, place the bottom of the carrying case on the pack, and turn the bottom knob clockwise.
• Removing a Model 41A Disc Pack (Model 42 Drive, bottom pack): Place the top of the carrying case on the pack. Press the release knob on the top of the case and lift the case off. Hold the pack upside down, place the bottom of the carrying case on the pack, and turn the bottom knob clockwise.
• SAFETY CAUTIONS: Before lifting the cover to the disc pack compartment, ensure the START/STOP switch is in STOP and the pack has halted to prevent shearing a locking pin. Never turn off POWER while the disc pack is rotating and the read/write head mechanism is extended, as this can damage the pack. Always move START/STOP to STOP and wait for the pack to halt before turning off power.

Condition Code Summary:

• 1 (Error): Sector could not be read, or read/write heads positioned at wrong track.
• 2 (Normal): Operation successful.
• 3 (Flag): Instruction addressed non-existent arm (arm 2) of Model 42, sector could not be written on, attempted to read a "bad" sector, or attempted to read/write an uninitialized sector.
• 4 and 1 (Fault): Disc drive not on-line, or FILE UNSAFE condition sensed during read/write operation.