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IBM PS/2 Model 70

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Revision as of 00:07, 22 September 2026 by Josh (talk | contribs) (Planar table: ardent-tool gives conflicting FRU numbers for the 16/20 MHz boards across its own pages - restructure the table by board type and state the conflict rather than picking one)
IBM Personal System/2 Model 70 386
IBM PS/2 Model 70 (8570) low-profile desktop
Specifications
DeveloperIBM Entry Systems Division, Boca Raton
ManufacturerIBM
TypeDesktop personal computer
ReleasedAnnounced 2 June 1988 (8570-E61, -121, -A21)
CPUIntel 80386DX at 16 MHz (-E61), 20 MHz (-121, -061, -081, -161) or 25 MHz with 64 KB L2 cache (-A61, -A21, -A81, -A16); Intel i486 at 25 MHz on the Model 70 486 (-B61, -B21) and on 25 MHz machines fitted with the 486/25 Power Platform. Socket for an 80387DX on the 386 machines
Memory1 MB (-E61), 2 MB (-061, -121, -A61, -A21, -B61, -B21) or 4 MB (-081, -161, -A81, -A16) as supplied. Three 72-pin parity SIMM sockets on the 16/20 MHz planars, maximum 6 MB; four on the 25 MHz planars, maximum 8 MB. 16 MB system maximum using Micro Channel memory adapters
Storage1.44 MB 3.5-inch diskette drive, with a position for a second; 60, 80, 120 or 160 MB DBA-ESDI fixed disk with the controller integrated into the drive
DisplayVGA on the planar, 15-pin D-sub; 640 ร— 480 in 16 colours, 320 ร— 200 in 256 colours, 720 ร— 400 text
SoundSpeaker in the battery/speaker assembly
Dimensions360 mm wide ร— 420 mm deep ร— 140 mm high
Weight9.55 kg
OS / FirmwareIBM PC DOS 3.30 and later; IBM OS/2 1.x; IBM AIX PS/2
SuccessorIBM PS/2 Model 70 486 (8570-B61 / B21), December 1989
Model no.8570

The IBM Personal System/2 Model 70 386 (IBM machine type 8570) is a 32-bit, 80386DX-based low-profile desktop announced on 2 June 1988. It shares its chassis, power-supply form factor and drive-riser arrangement with the Model 50, and its 32-bit Micro Channel implementation with the Model 80 tower.[1][2]

Two things distinguish it from the rest of the desktop line. Its fixed disk is a Direct Bus Attachment (DBA-ESDI) unit with the controller built into the drive, plugged into the drive riser rather than into an adapter card.[1][3] And the 25 MHz machines carry the processor on a separate processor board, which is what made the 486/25 Power Platform upgrade possible.[4][5]

Submodels

IBM PS/2 Model 70 386 and Model 70 486 submodels
Submodel Processor Supplied RAM Fixed disk Announced US launch price
8570-E61 80386DX-16 1 MB 60 MB 2 June 1988 $5,995
8570-121 80386DX-20 2 MB 120 MB 2 June 1988 $7,995
8570-A21 80386DX-25, 64 KB cache 2 MB 120 MB 2 June 1988 $11,295
8570-061 80386DX-20 2 MB 60 MB 26 September 1989 $5,795
8570-A61 80386DX-25, 64 KB cache 2 MB 60 MB 26 September 1989 $8,395
8570-B61 i486-25 2 MB 60 MB 19 December 1989 $12,390
8570-B21 i486-25 2 MB 120 MB 19 December 1989 $12,990
8570-081 80386DX-20 4 MB 80 MB 11 June 1991 โ€”
8570-161 80386DX-20 4 MB 160 MB 11 June 1991 โ€”
8570-A81 80386DX-25, 64 KB cache 4 MB 80 MB 11 June 1991 โ€”
8570-A16 80386DX-25, 64 KB cache 4 MB 160 MB 11 June 1991 โ€”

[1][6][7][8][9][10]

Planar Types

Four planar designs were used, and they are not interchangeable. Which one you have decides how much memory fits, what speed of SIMM it will take and whether a Power Platform can be installed.[10]

8570 planars
Type Board Speed Models SIMM sockets Board maximum
Type 1 Long 16 or 20 MHz -E61, -061, -081, -121, -161 Three (J30โ€“J32) 6 MB
Type 2 Short 20 MHz -061, -081, -121, -161 Three (J7, J9, J10) 6 MB
Type 3 โ€” 25 MHz, 80386DX on a processor card -A61, -A21, -A81, -A16 Four (J17, J18, J20, J21) 8 MB
Type 4 โ€” 25 MHz, i486 on a processor card -B61, -B21 Four (J17, J18, J20, J21) 8 MB

The 25 MHz planars are FRU 92F0580 (386) and FRU 41G3979 (486). FRU numbers for the 16 and 20 MHz boards are quoted inconsistently in the sources โ€” ardent-tool's planar pages give 96F7309 or 41G3984 for the Type 1 and 96F7308 or 41G3985 for the Type 2, while Tim O'Connor's cross-reference on the same site assigns 93F7309 and 96F7308 to the long boards and 41G3984 and 41G3985 to the short ones. Read the FRU label on your own board rather than relying on either.[10][11][12][4]

The 16 and 20 MHz planars take 85 ns parity SIMMs; the 25 MHz planars require 80 ns parity SIMMs and IBM documented the 2 MB 80 ns part as the only supported module for them. Fill the 25 MHz sockets starting at J21 and J20 โ€” starting at J17 or J18 has been reported to produce a 215 error.[10][4]

Whichever planar is fitted, the ceiling for the whole system is 16 MB, because the Micro Channel DMA controller has only 24 address lines.[10]

Planar

  • Processor. On the 16 and 20 MHz planars the 80386DX sits directly on the board (U143 on the Type 1). On the 25 MHz planars it is on a separate processor card in socket J15.[11][4]
  • Cache. None on the 16 and 20 MHz machines. The 25 MHz 386 processor board carries an Intel 82385-25 cache controller and eight 8 K ร— 8 SRAMs, giving 64 KB of L2.[4][6]
  • Coprocessor. A socket for an 80387DX beside the processor on the 386 machines. The i486 has its floating-point unit on-die and needs no external part.[8]
  • Real-time clock. A Motorola MC146818A soldered to the planar โ€” U150 on the Type 1, U81 on the Type 2, U143 on the Type 3/4 โ€” with a 32.768 kHz crystal beside it. It holds only the 64 bytes of CMOS; the Micro Channel configuration lives in a separate 2 K ร— 8 SRAM (U145 on the Type 1, U79 on the Type 2). There is no Dallas RTC module on this planar and no battery inside the clock chip.[11][12][4]
  • Battery. A separate 6 V two-cell lithium pack, FRU 72X8498, held in the battery/speaker assembly FRU 33F5950 and connected to the planar at J19 (Type 1 and 25 MHz, card-edge) or J14 (Type 2, 6-pin header).[13][14]
  • Video. VGA on the planar โ€” a 15F6864 or 90X8941 VGA controller, an INMOS IMSG171 RAMDAC and eight 64 K ร— 4 DRAMs for 256 KB of video memory. 640 ร— 480 in 16 colours, 320 ร— 200 in 256 colours, 720 ร— 400 text.[11][12][1]
  • Micro Channel. Three slots: two 32-bit (J2, J3) and one 16-bit with the auxiliary video extension (J1). IBM's own announcement describes them as "two 32-bit bus slots and one 16-bit bus slot with video extension".[1][11]
  • Diskette and fixed disk. Both go through the drive riser in J34 (Type 1) or J16 (Type 3/4). The riser, FRU 90X1111, carries two floppy connectors and the DBA-ESDI edge connector.[15][11]
  • Ports. Keyboard and auxiliary device (mini-DIN-6), serial (DB-25), parallel and VGA, all on the rear edge of the planar. A fuse on the planar protects the keyboard and auxiliary-device supply; F1 on the Type 2 planar is labelled as the keyboard/mouse fuse.[12][11]

What Actually Fails

The Model 70 planar does not carry surface-mount aluminium electrolytic capacitors. Photographs of the 8570 planars show through-hole dipped tantalum beads and surface-mount ceramics for rail decoupling. The electrolyte leakage that ruins some PS/2 assemblies is not this board's failure mode, and there is nothing on it to reflow or replace on suspicion.[11][12]

Where the leakage problem is real on this machine is in the drives: the diskette drive's logic board and the DBA-ESDI fixed disk's logic board both use surface-mount electrolytics, and both are documented as failing.[16][17] See IBM PS/2 Model 70 Capacitor Replacement Guide.

The 486/25 Power Platform

The 486/25 Power Platform, announced on 20 June 1989 as feature #5220 (P/N 6450876) at US$3,995, replaces the 386 processor board in a 25 MHz Model 70 with a board carrying an Intel i486 at 25 MHz. The kit also includes two EPROMs to bring the system board's firmware up to the level the i486 needs.[5][4]

  • It fits the 25 MHz machines only โ€” the -A61 and -A21 originally, later also the -A81 and -A16. It cannot be fitted to a 16 or 20 MHz planar, which has no processor card socket.[5][9][4]
  • The Power Platform board, FRU 64F0123 (P/N 64F1398), carries essentially only the 486DX-25 and a 50 MHz oscillator.[4]
  • It removes the 64 KB L2 cache. The 386 processor board it replaces carries the 82385 controller and its SRAMs; the 486 board does not. What you gain is the i486's 8 KB internal cache and its internal floating-point unit.[4][8]
  • Every known sample of the 486 processor board has factory rework wires on it. That is normal, not damage.[4]
  • A factory-built Model 70 486 (-B61 or -B21) is the same arrangement shipped from IBM rather than fitted in the field.[8]

Power Supply

A 132 W automatic voltage-sensing supply, made by ASTEC as model AA15530 and carrying IBM P/N 90X9409 and FRU P/N 90X8626. It mates with a 50-pin edge connector on the planar and supplies three DC rails โ€” +5 V, +12 V and −12 V โ€” plus System Status and Power Good signals. There is no −5 V rail.[1][15][18]

The Model 50's 94 W supply uses the same connector but is not rated for this machine's load. Rail limits, the connector pinout and the supply's protection behaviour are on the maintenance page.[15][18]

Fixed Disk

The Model 70's fixed disk is a DBA-ESDI unit: the controller is built into the drive and the drive plugs straight into the drive riser through a 2 ร— 36-pin edge connector carrying a subset of the 16-bit Micro Channel signals. There is no fixed-disk adapter card to remove, and no separate ESDI cable.[1][3]

Because the bus subset omits the top eight address lines, the interface addresses 64 KB rather than 16 MB. The controller presents itself to the Reference Diskette as AdapterID DF9F, "Integrated Fixed Disk and Controller".[3][10]

IBM's published geometry for the two launch drives:[1]

8570 launch fixed disks
Capacity Cylinders Heads Sectors/track Transfer rate Average access
60 MB 762 6 26 8.4 Mbit/s 27 ms
120 MB 920 8 32 10.2 Mbit/s 23 ms

The 1991 submodels use 80 MB and 160 MB drives.[9]

Reference Diskette

Configuration is held in CMOS and set from a Reference Diskette rather than from a BIOS setup screen. The Reference Diskette provides Set Configuration and Automatic Configuration, Set Features, the power-on password functions, and Advanced Diagnostics (Ctrl-A from the main menu). The 386 machines and the 486 machines use different Reference Diskette images.[10][4]

Physical and Electrical Specifications

Model 70 โ€” IBM published figures
Item Value
Width ร— depth ร— height 360 ร— 420 ร— 140 mm
Weight 9.55 kg
Heat output 215 W (735 BTU/hour)
Mains input 100โ€“125 V at 4 A maximum, or 200โ€“240 V at 2 A maximum, 50โ€“60 Hz, range selected automatically
Operating temperature 15.6 to 32.2 ยฐC
Keyboard port, maximum allowable current 275 mA
Auxiliary device port, maximum allowable current 300 mA
16-bit Micro Channel connector, maximum load 1.6 A at +5 V, 0.175 A at +12 V, 0.040 A at −12 V
32-bit Micro Channel connector, maximum load 2.0 A at +5 V, 0.175 A at +12 V, 0.040 A at −12 V

[18][1]

Common Faults

  • Lost configuration, a clock that does not advance, or 161 / 163 at POST. The 6 V lithium pack is flat or the battery/speaker assembly is faulty. See IBM PS/2 Model 70 Maintenance Guide.[13][19]
  • Diskette faults and 6xx errors. Failed surface-mount electrolytics on the drive's logic board, or a mechanical fault in the head carriage. See IBM PS/2 Model 70 Capacitor Replacement Guide.[16]
  • 104xx fixed-disk errors. 010455 and 010456 are controller errors, 010462 a controller seek error, 010464 a drive read error. IBM's FRU order for the read/write codes on this machine is diagnostics, then the riser card, then the drive, then the system board.[19]
  • A drive that will not spin up after long storage. Stiction, not electronics.[20]
  • 165 after changing an adapter. Run Automatic Configuration from the Reference Diskette.[19]
  • Adapters that are not seen, or intermittent Micro Channel faults. Clean the card edges and the slots before suspecting anything else.
  • Model 70 386 system unit
    Model 70 386 system unit
  • Front view showing the diskette drive position
    Front view showing the diskette drive position
  • 8570-121 planar (20 MHz)
    8570-121 planar (20 MHz)
  • Bare Model 70 planar
    Bare Model 70 planar
  • Front-bezel "Model 70 386" badge
    Front-bezel "Model 70 386" badge
  • "Model 70 486" badge (8570-B21 / B61)
    "Model 70 486" badge (8570-B21 / B61)

References

  1. โ†‘ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 IBM Announcement Letter 188-079, "IBM Personal System/2 Model 70 386 (8570 E61/121)", 2 June 1988, reproduced at ardent-tool.com. Source for the launch prices, the three I/O slots ("two 32-bit bus slots and one 16-bit bus slot with video extension"), the 132-watt automatic voltage-sensing power supply, the 6 MB system-board memory ceiling, the fixed disk "with integrated controller" and its published geometry, the second diskette-drive position, and the physical and electrical specifications.
  2. โ†‘ 8550 and 8570 โ€” Common Devices, Ardent Tool of Capitalism. Source for the cover-removal procedure, the drive-structure removal tool stowed under the battery/speaker assembly, the three planar screws plus three EMC-shield screws, and the planar positioning pin.
  3. โ†‘ 3.0 3.1 3.2 IBM DBA-ESDI Hard Drives, Ardent Tool of Capitalism. Source for the list of systems using Direct Bus Attachment (the Model 70 by drive-riser connector), the 2 ร— 36-pin edge-connector pinout transcribed from the Model 70 technical reference, and the component map of the WD387 60 MB drive logic board.
  4. โ†‘ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 8570 Type 3 & 4 Planar, Ardent Tool of Capitalism. Source for the 25 MHz planar map (J15 processor-card socket, J17/J18/J20/J21 SIMM sockets, J19 battery/speaker card-edge connector, U143 MC146818AFN RTC), the 386 processor board (FRU 15F7659 / P/N 64F3703, with an Intel 82385-25 cache controller and eight 8 K ร— 8 SRAMs), the 486/25 Power Platform board (FRU 64F0123, P/N 64F1398, carrying only the 486DX-25 and a 50 MHz oscillator), the SIMM type and population order, and ECAs 021, 029 and 092.
  5. โ†‘ 5.0 5.1 5.2 IBM Announcement Letter 189-102, "IBM Personal System/2 486/25 Power Platform", 20 June 1989, reproduced at ardent-tool.com. Source for the Power Platform's role as an upgrade for the Model 70 386, its feature number 5220 and part number 6450876, and its US$3,995 price.
  6. โ†‘ 6.0 6.1 IBM Announcement Letter 188-078, "IBM Personal System/2 Model 70 386 (8570-A21)", 2 June 1988, reproduced at ardent-tool.com. Source for the 25 MHz submodel's 82385 memory cache controller and 64 KB cache, its 2 MB standard memory and its US$11,295 launch price.
  7. โ†‘ IBM Announcement Letter 189-144, "New Models of IBM Personal System/2 Model 70 386 (8570-061 and 8570-A61)", 26 September 1989, reproduced at ardent-tool.com. Source for the -061 and -A61 configurations and prices, and for the system-board memory ceilings of 6 MB (-061) and 8 MB (-A61).
  8. โ†‘ 8.0 8.1 8.2 8.3 IBM Announcement Letter 189-196, "Personal System/2 Model 70 486 (8570-B61 and 8570-B21)", 19 December 1989, reproduced at ardent-tool.com. Source for the Model 70 486 configurations and prices, and for the i486's internal cache controller, internal 8 KB cache and internal floating-point unit.
  9. โ†‘ 9.0 9.1 9.2 IBM Announcement Letter 191-079, "IBM Personal System/2 Model 70 386 (081, 161, A81 and A16)", 11 June 1991, reproduced at ardent-tool.com. Source for the four 1991 submodels with 4 MB standard memory and 80 MB or 160 MB fixed disks, and for their physical specifications.
  10. โ†‘ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 8570 โ€” Common Devices, Ardent Tool of Capitalism (Louis Ohland / Tomรกลก Slavotรญnek). Source for the submodel list, Tim O'Connor's model-type-to-planar and FRU cross-reference, the system-board memory minima and maxima, the SIMM speed requirement and the integrated fixed-disk controller's ADF (AdapterID DF9F).
  11. โ†‘ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 11.7 8570 Type 1 Planar, Ardent Tool of Capitalism. Component-designator map for the 16/20 MHz planar: J1 16-bit Micro Channel slot with auxiliary video extension, J2 and J3 32-bit slots, J19 battery/speaker connector, J30โ€“J32 72-pin SIMM sockets, J34 floppy/hard-drive riser slot, J36 power-supply edge connector, U150 Motorola MC146818A RTC/CMOS and U145 NEC ยตPD446G-20L 2 K ร— 8 SRAM holding the Micro Channel configuration.
  12. โ†‘ 12.0 12.1 12.2 12.3 12.4 8570 Type 2 Planar, Ardent Tool of Capitalism. Component-designator map for the 20 MHz short planar: F1 keyboard/mouse fuse, J7/J9/J10 72-pin SIMM sockets, J11 and J12 32-bit Micro Channel slots, J13 16-bit slot with auxiliary video extension, J14 battery/speaker connector, U81 MC146818AFN RTC/CMOS and U79 Hitachi HM6264LFP-15T configuration SRAM.
  13. โ†‘ 13.0 13.1 Battery/Speaker Assembly, Ardent Tool of Capitalism. Source for the assembly FRU 33F5950, the battery FRU 72X8498, both connector pinouts (speaker data, ground, +6 V battery, Clear POP) and the power-on-password clearing procedure for Models 50, 50 Z, 60, 65 SX, 70 and 80.
  14. โ†‘ PS/2 Batteries, Ardent Tool of Capitalism, based on content by Bob Eager and Peter H. Wendt. Cross-reference of PS/2 models to battery types: the Model 70 and the Model 80 both take FRU 72X8498, a 6 V two-cell lithium pack equivalent to a CR-P2 / DL223A / EL223AP / K223LA / PC223 camera battery.
  15. โ†‘ 15.0 15.1 15.2 8550 / 8570 / 756x โ€” Power Supply, Ardent Tool of Capitalism. Secondary source reproducing IBM's 50-pin planar power-connector pinout and service test-voltage table, plus the ASTEC AA15530 identification, the 132 W rating, IBM P/N 90X9409 and FRU P/N 90X8626, the security-Torx case fixings, the two ASTEC 5 A 250 V fast-blow fuses F1 and F2, and the drive-riser card FRU 90X1111 with its two floppy connectors and DBA-ESDI connector.
  16. โ†‘ 16.0 16.1 8580 Diskette Drives, Ardent Tool of Capitalism, content by Fred Spencer and Al Savage. Source for the PS/2 diskette-drive part numbers (P/N 90X6766, FRU 72X8523 card-edge; FRU 64F0162 pin-interface), for Al Savage's teardown of a Mitsubishi MF355W-99M3 identifying five failed surface-mount electrolytics โ€” two 22 ยตF/16 V, one 1 ยตF/50 V and two 0.22 ยตF/50 V โ€” for the diskette-controller dirt problem under the power-supply fan, and for Peter Wendt's list of mechanical causes of a 162 at POST.
  17. โ†‘ PS/2 Surface Mount Capacitors, ibmfiles.com. Community teardown source; documents surface-mount electrolytic failure and pad corrosion on PS/2 Mitsubishi diskette drives and on the DBA hard-drive logic boards, and the technique of fitting through-hole parts to the surface-mount pads.
  18. โ†‘ 18.0 18.1 18.2 IBM, IBM Personal System/2 Model 70 386 Technical Reference, 4th edition, October 1990 โ€” hosted on this wiki as File:IBM PS2 Model 70 Technical Reference Oct90.pdf. Section 1: "Physical Specifications", "Power Supply", "Outputs", "Output Protection", "Voltage Sequencing", "Component Maximum Current" and "Channel Load Current".
  19. โ†‘ 19.0 19.1 19.2 PS/2 Error Codes and the linked code tables 160โ€“199, 300โ€“999 and 10000โ€“11999, Ardent Tool of Capitalism. Secondary source; the tables reproduce IBM's own symptom-to-FRU lists.
  20. โ†‘ Known Problems โ€” Experience, RETAIN Tips, ECAs, Ardent Tool of Capitalism. Source for Peter Wendt's account of hard-disk stiction and the recovery options.


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