Seagate ST-251

The Seagate ST-251 was a 42MB, 5.25" half-hieght MFM stepper-motor hard disk, available from 1990. It was available in three varients - the original ST-251, with 40ms average seek, and the later ST-251-0 and ST-251-1, with a 28ms average seek.

The device automatically parked disk heads on power down, and although noisy in operation, became known for its reliability.

Specifications

• Formatted Capacity: 42.8 MB
• Recording Method: MFM
• Interface: ST412
• Actuator: Stepper
• Configuration: 820 cylinders, 6 heads, 17 SPT, auto-park
• Average Access: 40ms (ST251) / 28ms (ST251-0 and ST251-1)
• Power Consumption: 12 W (typical)
• IBM AT Drive Type: 44, 40, or 3

Seagate Product Documentation

<source lang="text">

                        SEAGATE TECHNOLOGY, INC.
                             1-800-SEAGATE
                         http://www.seagate.com
                           (C)opyright 1991

ST-251 ST412 MFM

                                                         /─4─3─2─1─\
                                                         │ O O O O │ Power
             o o o o o o o o                             └─────────┘
 ┌Data Cable o o o o o o o o  ┌Controller Cable    1       5 G G 12
═════════ ══ │ │ │ │ │ │ │ │ ════════════════════ ═══   ════════════
             │ │ │ │ │ │ │ │ 1────────────┐
             │ │ │ │ │ │ │ │ └─Terminator─┘
             │ │ │ │ │ │ │ │

Drive Select->1 2 3 4 │ │ │ └ Radial

               │ │ │ │ │ └── Reserved
               │ └┬┘ │ └──── Write Fault
               │  │  └────── Factory Test
               │  └───────── Never Used (Drive Select 3 and 4)
               └ If twisted cable, use Drive Select 2

                         ST - 251

      UNFORMATTED CAPACITY (MB) ________________51.2
      FORMATTED CAPACITY (17 SECTORS) (MB) _____42.8
      ACTUATOR TYPE ____________________________STEPPER
      TRACKS ___________________________________4,920
      CYLINDERS ________________________________820
      HEADS ____________________________________6
      DISCS ____________________________________3
      MEDIA TYPE _______________________________THIN FILM
      RECORDING METHOD _________________________MFM
      TRANSFER RATE (mbits/sec) ________________5.0
      SPINDLE SPEED (RPM) ______________________3,600
      AVERAGE LATENCY (mSEC) ___________________8.3
      INTERFACE ________________________________ST412
      SECTORS PER DRIVE ________________________83,640
      TPI (TRACKS PER INCH) ____________________777
      BPI (BITS PER INCH) ______________________9,935
      AVERAGE ACCESS (ms) ______________________40/28*
      SINGLE TRACK SEEK (ms) ___________________8
      MAX FULL SEEK (ms) _______________________ /70
      MTBF (power-on hours) ____________________100,000
      POWER REQUIREMENTS: +12V START-UP (amps) _2.0/2.5*
                          +12V TYPICAL (amps) __0.5
                          +5V TYPICAL (amps) ___1.0/1.2*
                          TYPICAL (watts) ______11/12*
                          MAXIMUM (watts) ______29/36*
      BUFFERED STEP PULSE RATE (micro sec) _____3-200
      WRITE PRECOMP (cyl) ______________________N/A (821)
      REDUCED WRITE CURRENT (cyl) ______________N/A (821)
      LANDING ZONE (cyl)________________________AUTO PARK
      IBM AT DRIVE TYPE ________________________44, 40, or 3**

      *ST251-0/ST251-1
      **MAY REQUIRE PARTITIONING SOFTWARE

Seagate reserves the right to change, without notice, product offerings or specifications. (6/26/90) </source>

(Source: Seagate FTP server)

Connections

(Source: Seagate Web Site)

Heads

The device used ferrite heads - the most simple type.

Notes

• The ST-251-1 model was routinely used on RLL controllers and, despite not being certified other than for MFM use, would usually provide years of reliable service in such configuration. RLL provides a 50% capacity and sequential throughput advantage.

See Also

• Seagate ST11M, an 8-bit MFM controller suitable for use with the drive
• Seagate MFM Hard Drive Repair Notes