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

                         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: 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