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Point the documentation list at IBM Announcement Letter 187-148: PS/2 Model 25
 
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| name          = IBM Personal System/2 Model 25
| name          = IBM Personal System/2 Model 25
| logo          = [[File:IBM PS2 Model 25 8086 badge.svg|150px]]
| logo          = [[File:IBM PS2 Model 25 8086 badge.svg|150px]]
| image        = [[File:IBM PS2 Model 25.jpg|260px]]
| image        = [[File:IBM PS2 Model 25.jpg|260px|frameless]]
| caption      = IBM PS/2 Model 25 (8525)
| caption      = IBM PS/2 Model 25 (8525)
| developer    = IBM Entry Systems Division, Boca Raton
| manufacturer  = IBM
| manufacturer  = IBM
| type          = All-in-one personal computer
| type          = All-in-one personal computer
| release date  = August 4, 1987 (Model 25 8086); May 1990 (Model 25 286); April 1992 (Model 25 SX)
| release date  = 4 August 1987 (Model 25); 1 June 1990 (Model 25 286); 17 April 1992 (Model 25 SX)
| discontinued  = November 17, 1992 (Model 25 286)
| price        = US$1,350 (8525-001) to US$1,740 (8525-G04) at launch
| cpu          = Intel 8086 @ 8 MHz (Model 25) / Intel 80286 @ 10 MHz, 1 wait state (Model 25 286) / Intel 80386SX @ 16 or 20 MHz (Model 25 SX)
| cpu          = Intel 8086 at 8 MHz, no wait states; 80286 at 10 MHz (Model 25 286); 386SX at 16 MHz (Model 25 SX)
| memory        = 512 KB – 640 KB (Model 25); 1 MB – 4 MB (Model 25 286); 1 MB – 16 MB (Model 25 SX)
| memory        = 512 KB, 640 KB maximum on the system board (8086); 0.5 to 4 MB on the board (286); 1 or 4 MB, 16 MB maximum (SX)
| storage      = One or two 3.5" 720 KB diskette drives (Model 25); one 1.44 MB diskette drive + optional 30 MB ST-506 MFM hard drive (Model 25 286); 1.44 MB diskette + IDE hard drive (Model 25 SX)
| storage      = One or two 3.5-inch diskette drives (720 KB on the 8086, 1.44 MB on the 286 and SX); optional fixed disk
| display      = Integrated 12" CRT (mono or colour). MCGA (Model 25), VGA (Model 25 286), Super VGA (Model 25 SX)
| display      = Integrated 12-inch analogue display, monochrome or colour; MCGA (8086), VGA (286 and SX)
| sound        = PC speaker; 1/4" mono earphone jack on rear of system unit
| sound        = Beeper; earphone connector
| dimensions    = 382 H × 320 W × 375 D mm (System unit + integrated display)
| dimensions    = 382 × 320 × 375 mm (H × W × D)
| weight        = 12.7 kg (28 lb) monochrome (001); 16.8 kg (37 lb) colour (004)
| weight        = 14.1 kg monochrome, 16.3 kg colour (8086, IBM US); 16.0 to 17.7 kg (286 and SX)
| os            = IBM PC DOS 3.3 (Model 25); IBM PC DOS 3.3 / 4.0 / OS/2 EE 1.0/1.2 (Model 25 286); IBM PC DOS 5.0 (Model 25 SX)
| os            = IBM PC DOS 3.30 and later; DOS 5.0 shipped with the SX
| predecessor  = none (entry-level PS/2 replaces the [[IBM PC (5150)]]/[[IBM PC XT (5160)|XT]] in the IBM range)
| predecessor  = [[IBM PC (5150)]], [[IBM PC XT (5160)]]
| successor    = IBM PS/1 series (consumer market); IBM PS/ValuePoint
| model        = 8525
| model        = 8525
}}
}}


The '''IBM Personal System/2 Model 25''' (machine type '''8525''') is the lowest-end entry in the IBM Personal System/2 (PS/2) family of personal computers. It was announced on August 4, 1987 as the fifth PS/2 model, four months after IBM unveiled the rest of the PS/2 line on April 2, 1987. The Model 25 was IBM's first PS/2 sold into the home and education market and was the only PS/2 with an '''integrated CRT''' in a Macintosh-style all-in-one case. Unlike most other PS/2 models, the Model 25 uses '''ISA''' expansion slots (not Micro Channel), making it electrically compatible with PC/XT and PC/AT expansion cards but '''not''' with the higher PS/2 models.
The '''IBM Personal System/2 Model 25''' (machine type 8525) is the all-in-one member of IBM's PS/2 range: the system board, drives and supply share one case with a 12-inch display. IBM announced it on 4 August 1987 as a low-priced machine running at about twice the speed of the 8088-based IBM PCs, with an 8086 at 8 MHz, MCGA graphics and two slots for existing PC and XT cards.<ref name="ann187148">IBM, Announcement Letter 187-148, "IBM 8525, Personal System/2 Model 25", 4 August 1987, hosted as [[:File:IBM Announcement Letter 187-148 PS2 Model 25 (August 1987).pdf]]. Description, standard features, prices, availability dates, physical specifications, universal power supply and compatibility notes.</ref> Like the [[IBM PS/2 Model 30|Model 30]] it has ISA slots; IBM kept Micro Channel for the higher models.<ref name="dosdays" /> IBM later sold a Model 25 286 (1990) and a Model 25 SX for schools (1992).


The Model 25 was sold in three CPU generations:
== History ==


* '''Model 25''' (8086 at 8 MHz, MCGA video, 8-bit ISA, August 1987&ndash;1990)
The first four models, 001 and G01 (monochrome) and 004 and G04 (colour), were priced at US$1,350, $1,395, $1,695 and $1,740. The 001 and 004 were available on the day of announcement and the G models, with the Enhanced Keyboard instead of the Space Saving Keyboard, from 30 October 1987.<ref name="ann187148" /> IBM Canada listed the 001 and 004 at $2,095 and $2,595.<ref name="qref25">IBM Canada Ltd, Quick Reference, "IBM Personal System/2 Model 25", transcribed at [https://www.ardent-tool.com/qtechinfo/8525.html ardent-tool.com]. Canadian prices, memory type, weights, supply ratings and MCGA summary.</ref>
* '''Model 25 286''' (80286 at 10 MHz, VGA, 16-bit ISA, May 1990&ndash;November 1992)
* '''Model 25 SX''' (80386SX at 16 or 20 MHz, Super VGA, 16-bit ISA, K&ndash;12 education market only, April 1992&ndash;)


All three generations share the all-in-one chassis, the 12" CRT, and the PS/2-family proprietary floppy and hard-disk power and data connectors. The Model 25 was '''never officially sold outside the United States''' in its original form, although Canadian-French keyboard variants (suffixed -F0x) were available, and the Collegiate variant was bundled with PC DOS 3.30 and Microsoft Windows 1.04.
The Model 25 LS (8525-L01 monochrome and L04 colour), announced on 2 June 1988, came with 640 KB, the Enhanced Keyboard and an IBM Token-Ring Network PC Adapter, at US$2,139 and $2,484 through dealers.<ref name="ann188081">IBM, Announcement Letter 188-081, "IBM Personal System/2 Model 25 LS", 2 June 1988, transcribed at [https://www.ardent-tool.com/8525/188-081.txt ardent-tool.com].</ref>


== History ==
The Model 25 286 (8525-006, G06, 036, G36) was announced on 10 May 1990 for availability on 1 June 1990. It has an 80286 at 10 MHz with one wait state, 0.5 or 1 MB on the system board expandable to 4 MB, 1.44 MB diskette support and VGA, and the 036 and G36 have a 30 MB fixed disk. Prices ran from US$2,295 to $3,040. IBM noted that the new drive options announced with it do not fit earlier 8525 models.<ref name="ann190082">IBM, Announcement Letter 190-082, "IBM Personal System/2 Model 25 286 (8525-006, G06, 036, G36)", 10 May 1990, transcribed at [https://www.ardent-tool.com/8525/190-082.txt ardent-tool.com]. Features, prices, 124.5 W supply, weights, BTU output and DOS support.</ref>
 
The Model 25 SX (8525-K00, K01, L02) was announced on 21 January 1992, available from 17 April 1992, and sold through IBM's K-12 education channels only. It has a 386SX at 16 MHz, 1 MB (K00) or 4 MB (K01, L02) of parity memory with a 16 MB maximum, VGA with 256-colour support, and DOS 5.0. The K01 adds an Ethernet adapter and the L02 a Token-Ring adapter, both with Remote Initial Program Load. Prices were US$2,082, $2,832 and $3,165.<ref name="ann192019">IBM, Announcement Letter 192-019, "IBM Personal System/2 Model 25 SX (8525-K00, K01, L02)", 21 January 1992, transcribed at [https://www.ardent-tool.com/8525/192-019.txt ardent-tool.com]. Features, prices, memory, LAN models, 124.5 W supply, dimensions and weight.</ref>


IBM announced the PS/2 line on April 2, 1987 with the Model 30 (8086, ISA), Model 50 (80286, MCA), Model 60 (80286, MCA) and Model 80 (80386, MCA). The '''Model 25''' followed on August 4, 1987 as a price-competitive entry aimed at home-office workers and students. Contemporary reviewers compared it favourably to Apple's original Macintosh because of its single-case form factor, although they criticised its lack of a standard hard drive.
== Models ==


The original announcement letter described the Model 25 as a "low price general-purpose computer system which provides enhanced function beyond that established by the IBM Personal Computer," and it was positioned as a direct retail replacement for the IBM PC (5150) and IBM PC XT (5160).
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''IBM PS/2 Model 25 models (IBM US announcement letters)'''
! Model !! Processor !! Memory as shipped !! Storage !! Display !! Notes
|-
| 8525-001, G01 || 8086, 8 MHz || 512 KB || One 720 KB diskette || Monochrome || G01 has the Enhanced Keyboard
|-
| 8525-004, G04 || 8086, 8 MHz || 512 KB || One 720 KB diskette || Colour || G04 has the Enhanced Keyboard
|-
| 8525-L01, L04 || 8086, 8 MHz || 640 KB || One 720 KB diskette || Monochrome / colour || Model 25 LS, Token-Ring adapter fitted
|-
| 8525-006, G06 || 80286, 10 MHz || 512 KB || One 1.44 MB diskette || Colour VGA || Model 25 286
|-
| 8525-036, G36 || 80286, 10 MHz || 1 MB || 1.44 MB diskette, 30 MB fixed disk || Colour VGA || Model 25 286
|-
| 8525-K00 || 386SX, 16 MHz || 1 MB || One 1.44 MB diskette || Colour VGA || Model 25 SX, education only
|-
| 8525-K01, L02 || 386SX, 16 MHz || 4 MB || One 1.44 MB diskette || Colour VGA || Ethernet (K01) or Token-Ring (L02)
|}


A '''Collegiate''' variant (8525-C02/C05/K02/K05) shipped with two floppy drives, 640 KB RAM, the IBM PS/2 Mouse, DOS 3.30 and Microsoft Windows 1.04. A '''Model 25 LS''' (8525-L01/L04) shipped with a Token Ring network card pre-installed.
Sources: 187-148, 188-081, 190-082 and 192-019.<ref name="ann187148" /><ref name="ann188081" /><ref name="ann190082" /><ref name="ann192019" />


The Model 25 286 was announced in May 1990 with a 80286 at 10 MHz, VGA video, a 1.44 MB diskette drive and (on the -036/-G36 submodels) a 30 MB ST-506 MFM hard drive. It was withdrawn from the IBM catalogue on November 17, 1992. The Model 25 SX was developed by IBM Boca Raton's team led by José García and sold only into K&ndash;12 schools from April 1992; it was the only Model 25 with an IDE hard drive interface.
== Architecture ==


== Submodels ==
=== Model 25 (8086) system board ===


The following list of Model 25 submodels is taken from the IBM Personal Computer Product Reference (Version 4.0, September 1988) and the IBM Canada Quick Reference.
There are three system boards: Type 1 (P/N 00F2073), Type 2 (FRU P/N 96F7390, P/N 64F0738) and a Japanese board (P/N 78X8943) made by Panasonic/Matsushita. The layouts differ, but the reference designators are largely the same across all of them and across the 8086 Model 30 boards.<ref name="at8525">Ardent Tool of Capitalism, [https://www.ardent-tool.com/8525/Planar.html "8525 Planar"], based on content by William R. Walsh. Designator lists for the Type 1, Type 2 and Japanese boards, ROM images, riser card, MCGA notes, power connector, diskette drive notes and ECA 023.</ref> IBM's 1994 maintenance manual lists 96F7390 as the system board FRU.<ref name="hmm">IBM, ''Personal System/2 Hardware Maintenance Manual'', S52G-9971-02, October 1994, hosted as [[IBM Personal System 2 Hardware Maintenance Manual (S52G-9971-02, October 1994)]]. General Checkout and Symptom-to-FRU Index (AT Bus), pp. 3 to 17; power supply connector, p. 138; system board locations, pp. 185 to 188; Model 25 parts, pp. 223 to 225.</ref>


{| class="wikitable styled-table" style="width:70%; text-align:center;"
{| class="wikitable styled-table" style="width:95%;"
|+'''Selected IBM PS/2 Model 25 submodels'''
|+'''Model 25 (8086) system board, principal parts (ardent-tool)'''
! Submodel !! CPU !! Clock !! Bus !! RAM (max) !! FDD !! HDD !! Monitor !! Keyboard !! Notes
! Designator !! Part
|-
| U10 || Intel 8086-2 CPU, 8 MHz
|-
| U13 || 8087 coprocessor socket
|-
| U8 || Intel P8253-5 timer
|-
|-
| 8525-001 || 8086 || 8 MHz (0 ws) || ISA 8-bit || 512 KB (640 KB) || 1 × 720 KB || none || 12" mono || Space-Saving || US $2,095 list
| U9, U11, U12, U14, U15 || IBM gate arrays 72X8203, 72X8300 (MCGA memory controller), 72X8205 (MCGA video formatter), 72X8206, 72X8202
|-
|-
| 8525-G01 || 8086 || 8 MHz || ISA 8-bit || 512 KB (640 KB) || 1 × 720 KB || none || 12" mono || Enhanced 101-key ||
| U5 || IMSG171P RAMDAC
|-
|-
| 8525-F01 || 8086 || 8 MHz || ISA 8-bit || 512 KB (640 KB) || 1 × 720 KB || none || 12" mono || Cdn-French SSK ||
| U6, U7 || HM53461P 64K × 4 DRAM (MCGA)
|-
|-
| 8525-004 || 8086 || 8 MHz || ISA 8-bit || 512 KB (640 KB) || 1 × 720 KB || none || 12" colour || Space-Saving || US $2,595 list
| U38 || CXK5864BM-12L 8K × 8 SRAM (MCGA)
|-
|-
| 8525-G04 || 8086 || 8 MHz || ISA 8-bit || 512 KB (640 KB) || 1 × 720 KB || none || 12" colour || Enhanced 101-key ||
| U16, U22, U34, U35 || NEC D4164C-10 DRAM
|-
|-
| 8525-C02 / -K02 || 8086 || 8 MHz || ISA 8-bit || 640 KB || 2 × 720 KB || none || 12" mono || varies || Collegiate kit
| ZM1, ZM2 || MSM3764A-15 64K × 1 DRAM
|-
|-
| 8525-C05 / -K05 || 8086 || 8 MHz || ISA 8-bit || 640 KB || 2 × 720 KB || none || 12" colour || varies || Collegiate kit
| U18 || µPD765AC-2 diskette controller
|-
|-
| 8525-L01 / -L04 || 8086 || 8 MHz || ISA 8-bit || 512 KB (640 KB) || 1 × 720 KB || none || 12" mono/colour || varies || Token Ring (LS)
| U19 || 8237A DMA controller
|-
|-
| 8525-006 || 80286 || 10 MHz (1 ws) || ISA 16-bit || 512 KB (4 MB) || 1 × 1.44 MB || none || 12" VGA colour || Space-Saving || US $2,295 list
| U27 || NS8250AV UART
|-
|-
| 8525-G06 || 80286 || 10 MHz || ISA 16-bit || 512 KB (4 MB) || 1 × 1.44 MB || none || 12" VGA colour || Enhanced 101-key ||
| F1, F2 || Fuses, probably mouse and keyboard (combined in F1 on the Type 2 board)
|-
|-
| 8525-036 || 80286 || 10 MHz || ISA 16-bit || 1 MB (4 MB) || 1 × 1.44 MB || 30 MB ST-506 || 12" VGA colour || Space-Saving || US $2,995 list
| J7 || Power connector
|-
|-
| 8525-G36 || 80286 || 10 MHz || ISA 16-bit || 1 MB (4 MB) || 1 × 1.44 MB || 30 MB ST-506 || 12" VGA colour || Enhanced 101-key ||
| J8 || Fan connector
|-
|-
| 8525-K00 || 386SX || 16 MHz (underclocked) || ISA 16-bit || 1 MB (16 MB) || 1 × 1.44 MB || IDE (opt.) || 12" SVGA colour || Enhanced || School market
| J9 || Memory (dual 30-pin sockets)
|-
|-
| 8525-K01 || 386SX || 16 MHz || ISA 16-bit || 4 MB (16 MB) || 1 × 1.44 MB || IDE (opt.) || 12" SVGA colour || Enhanced || + Ethernet
| J11 || 44-pin fixed-disk connector
|-
|-
| 8525-L02 || 386SX || 16 MHz || ISA 16-bit || 4 MB (16 MB) || 1 × 1.44 MB || IDE (opt.) || 12" SVGA colour || Enhanced || + Token Ring
| J12 || 40-pin diskette connector
|-
| Y1, Y2, Y3 || 14.31818 MHz, 25.175 MHz and 48.0 MHz oscillators
|}
|}


== Architecture ==
The 8086 Model 25 has no real-time clock: its BIOS system descriptor reports "No Real-time clock",<ref name="tr25bios">IBM, ''IBM Personal System/2 Model 25 Technical Reference'', June 1987, p. 5-45, hosted as [[IBM PS2 Model 25 Technical Reference (June 1987)]].</ref> and it is the only PS/2 without a CMOS battery.<ref name="atbatt">Ardent Tool of Capitalism, [https://www.ardent-tool.com/misc/batteries.html "PS/2 RTC/CMOS Batteries"], based on content by Bob Eager and Peter H. Wendt. Battery type and FRU for each model, DS1287 replacements, CR2032 test limits.</ref> The riser card (P/N 78X9031) carries two 8-bit ISA slots and a resistor pack.<ref name="at8525" /> The Model 25 does not use the same power connector as the 8086 Model 30.<ref name="at8525" />
 
=== Model 25 (8086) planar ===


The Model 25 8086 planar uses an Intel 8086-2 CPU at '''8 MHz, zero wait states''', with a socket at ZM1 (sic — '''not Uxx''', per the IBM planar silkscreen) for an optional '''Intel 8087''' math coprocessor. The chip complement is:
=== Model 25 286 system board ===


* '''Intel 8086-2''' (CPU) at 8 MHz.
The board (ardent-tool gives FRU P/N 64F0178, P/N 37F6675; IBM's 1994 manual lists FRU 96F7435) uses the VLSI VL82CPCAT chipset at ZM2 to ZM6, a 286-10 at ZM36 and a 287 socket at ZM1. Other parts: VL16C451 serial and parallel at ZM9, 27F4094 diskette gate array at ZM14, 15F6864 VGA controller at ZM18 with an IMSG171P-35 RAMDAC at ZM23, µPD765BC diskette controller at ZM19, 8042 keyboard controller at ZM33 and a Dallas DS1287 clock module at ZM35. Memory is 30-pin SIMMs with parity in J9 and J10. J13 is the password-override connector, and J7 and J14 are the power connectors.<ref name="at286">Ardent Tool of Capitalism, [https://www.ardent-tool.com/8525/Planar_286.html "8525-286 Planar"]. Designator list, ROM images, memory, earphone connector board and memory expansion address table.</ref><ref name="hmm" />
* '''IBM 72X8202 / 72X8203 / 72X8206''' &mdash; three IBM-fabricated PS/2 gate-array support chips (CPU/bus support, planar I/O glue, video).
* '''Intel P8253-5''' &mdash; programmable interval timer (system tick, refresh, speaker), at U8.
* '''Seiko Epson SLA64030J2L''' &mdash; clock generator / chip-set support (U11).
* '''Seiko Epson SLA6330J1C''' &mdash; chip-set support (U15).
* '''NEC D765AC-2''' &mdash; floppy disk controller, at U18.
* '''Siemens 8237A''' &mdash; DMA controller, at U19. (One 8237A on the Model 25, unlike the AT's pair.)
* '''National Semiconductor NS8250AV''' &mdash; UART for the serial port, at U27.
* '''Inmos IMSG171P''' &mdash; video RAMDAC for the integrated MCGA.
* '''ROM BIOS''' &mdash; two 32 KB EPROMs in sockets U13/U17 (also marked U10/U20 on some silkscreen revisions), 64 KB total, splitting CBIOS (Compatible BIOS for backward compatibility with PC DOS) and ABIOS (Advanced BIOS for OS/2).
* '''Sony CXK5864BM-12L''' &mdash; 8 KB static RAM, used for video character generator and BIOS work area, at U38.
* DRAM: NEC D4164C-10 chips (×4) at U16/U33/U34/U35 plus OKI M3764A-15 chips at U44 and ZM1, giving 512 KB on-planar with parity. Expansion uses an IBM-pinout 30-pin DIP/SMK RAM module for 128 KB to reach 640 KB.
* Crystals: '''Y1 = 14.318 18 MHz''' (software clock); '''Y2 = 25.175 MHz''' (video pixel clock); '''Y3 = 48.0 MHz''' (CPU/system clock master, divided by 6 for the 8086).
* '''F1''' fuse on the planar protects the keyboard/mouse +5 V rail.
* The 8086 Model 25 has '''no hardware real-time clock''' &mdash; date and time must be set manually from DOS at each boot. (The Model 25 286 and 25 SX both have a hardware RTC backed by a battery.)


The Model 25 and the Model 30 share substantially the same planar layout; many sources confirm that an 8525 8086 planar will physically and electrically swap with a 8530 planar.
=== Model 25 SX system board ===


=== Model 25 286 planar ===
The board (ardent-tool gives FRU P/N 87F4769 in "K" and "L" versions; IBM's 1994 manual lists 42G2802 with 1 MB and 42G2803 with 4 MB) has an i386SX at U2, clocked at 16 MHz from a 32 MHz oscillator; many are 20 MHz parts run at 16 MHz. The chipset is a VLSI VL82C304 and VL82C305, with an 8042 keyboard controller at U10, an 82077AA diskette controller at U25, ROM BIOS 87F4794 at U26, and IBM's 84F7985 SVGA controller at U42 with its own video RAM. Memory is soldered 512K × 9 DRAM plus one 72-pin SIMM socket at J6; J4 is an unfitted second socket. J10 is a 40-pin IDE connector, J14 a 4-pin hard-disk power connector, J2 the power-on password clear, and B1 a CR2032 cell for the clock, with a 32.768 kHz crystal at Y1.<ref name="atsx">Ardent Tool of Capitalism, [https://www.ardent-tool.com/8525/Planar_SX.html "8525 SX Planar"], based on content by William R. Walsh. Designator lists for the K and L boards, ROM image, unpopulated memory positions, the riser slot for the LAN adapter, the SVGA controller and the CPU speed.</ref><ref name="hmm" /> IBM's announcement mentions VGA only; the controller's SVGA modes work with IBM's VESA driver, though the built-in display cannot sync to 800 × 600.<ref name="ann192019" /><ref name="atsx" />


The Model 25 286 planar uses an Intel 80286 at '''10 MHz with 1 wait state to system memory''' and a '''VLSI VL82C100 / VL82C101 / VL82C102 / VL82C103 / VL82C104''' chipset (the "Popular AT" PC/AT-compatible chipset by VLSI). The system supports up to 4 MB of RAM on '''two 30-pin "MMK" parity SIMM''' sockets (J9/J10) with a proprietary IBM pinout, and includes a '''VGA''' graphics subsystem driven by the IBM 15F6864 VGA gate array (ZM18) and the '''Inmos IMSG171P-35''' RAMDAC (ZM23).
== Storage ==


Additional planar I/O on the Model 25 286:
Each diskette drive takes power and data through one cable from the system board; there is no separate drive power lead.<ref name="dosdays">DOS Days, [https://www.dosdays.co.uk/computers/IBM%20PS2%20Model%2025/ibm_ps2_model_25.php "IBM PS/2 Model 25"]. Community reference: drive cabling, drive makers, dust shutters and capacitor leakage, 1.44 MB support with Sony drives, and the Model 30 supply not fitting.</ref> PS/2 diskette drives were made mostly by Alps and Mitsubishi, with Sony and YE-Data less common.<ref name="dosdays" /> The 8086 machine shipped with 720 KB drives but has undocumented 1.44 MB support that works reliably only with Sony drives, and later system boards accept more drives than early ones.<ref name="at8525" />
* '''VLSI VL16C451''' &mdash; integrated UART + parallel port (ZM9).
* '''NEC D765BC''' &mdash; floppy disk controller (ZM19).
* '''Intel 8042''' &mdash; keyboard controller (ZM33), supporting the PS/2 keyboard and pointing device (PS/2 mouse) ports.
* '''27F4094 DISKGA''' &mdash; IBM disk/diskette gate array (ZM14), supporting the proprietary PS/2 single-cable floppy interface and the optional ST-506 hard drive interface.
* Crystals: Y1 = 14.318 MHz; Y2 = 25.175 MHz; Y3 = 20.322 MHz; Y4 = 20.0 MHz; Y5 = 48.0 MHz.
* The 286 planar adds a '''4-pin auxiliary power connector''' to feed the 16-bit ISA bus (not present on the 8086 Model 25), and a '''math coprocessor socket''' at ZM1 for an 80287.
* Battery-backed CMOS via the MC146818-equivalent RTC integrated into the VLSI chipset.


=== Model 25 SX planar ===
PS/2 3.5-inch drives are direct drive: Mitsubishi's MF355C specification describes a brushless DC motor turning the spindle directly at 300 rpm.<ref name="mf355c">Mitsubishi Electric, ''3.5 inch Flexible Disk Drive Standard Specifications, MF355C'', UGD-0527A, February 1987, section 3, hosted as [[:File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf]].</ref>


The Model 25 SX planar uses an Intel 80386SX (typically a 386SX-16 or a 386SX-20 underclocked to 16 MHz) at U2, with an '''80387SX''' socket at U5. The chipset is '''VLSI VL82C304 / VL82C305-FC'''. Additional features:
The Model 25 has no hard-disk controller on the system board. IBM describes its 44-pin fixed-disk connector as "a dedicated I/O channel for the connection of the IBM Personal System/2 20MB Fixed Disk Drive and controller, or similar attachment", carrying ordinary I/O-channel signals, a −DISK CS select decoded at hex 032x, a −Disk Installed line and address lines A0 to A2 to pick a register in the drive's controller.<ref name="tr25io">IBM, ''IBM Personal System/2 Model 25 Technical Reference'', June 1987, "Fixed Disk Connector", p. 1-104, hosted as [[IBM PS2 Model 25 Technical Reference (June 1987)]].</ref> The Model 25 SX is the only Model 25 with a 40-pin IDE connector.<ref name="atsx" />


* '''Intel 82077AA''' (U25) &mdash; floppy controller, supporting 1.44 MB diskettes natively.
== Display ==
* '''IBM SVGA gate array 84F7985''' (U42) with '''Toshiba TC511665BZ-80''' video RAM at U43/U44/U51/U54, driven by an IMSG171P RAMDAC at U45.
* '''Hitachi HM514900JP8''' &mdash; system RAM, with additional 30-pin socket pads at U33/U32/U48/U49 populated on non-K (non-school) variants.
* '''On-board IDE''' hard disk interface at J10 (the Model 25 and 25 286 use a proprietary ST-506 / PS/2 floppy interface; the 25 SX uses standard 40-pin IDE).
* On the K01 and L02 submodels, a second flipside ISA slot on the riser card carries an Ethernet or Token Ring card aligned to a rear-panel cutout.
 
== Memory ==
 
The Model 25 (8086) ships with 512 KB on-board and accepts a single '''128 KB IBM memory module''' (IBM P/N 78X8955) at a proprietary 30-pin RAM socket to reach the architectural ceiling of 640 KB. The on-board DRAM is DIP 41464-class and OKI M3764-class chips '''with parity'''.


The Model 25 286 has two proprietary 30-pin MMK '''parity SIMM sockets''' (J9/J10). The MMK pinout is similar to the standard JEDEC 30-pin SIMM but '''not interchangeable''': the IBM modules have different chip-select routing and require modules with the IBM-style edge connector. The largest supported configuration is 4 MB (2 × 2 MB).
The 8086 Model 25 has MCGA on the system board with a 64 KB display buffer. It supports the CGA modes plus 640 × 480 in 2 colours, 320 × 200 in 256 colours, and 40- and 80-column text in 16 colours with an 8 × 16 character box, all from 262,144 colours. It does not support the 640 × 350 mode or mode 7 for the IBM 5151 monochrome display. On the monochrome models the MCGA converts colour to up to 64 shades of grey.<ref name="ann187148" /> The palette has 256 18-bit registers driving three 6-bit DACs.<ref name="tr25vid">IBM, ''IBM Personal System/2 Model 25 Technical Reference'', June 1987, video subsystem, pp. 1-36 and 1-57, hosted as [[IBM PS2 Model 25 Technical Reference (June 1987)]].</ref> The Model 25 286 has VGA, and the Model 25 SX VGA with IBM's SVGA controller.<ref name="ann190082" /><ref name="atsx" />


The Model 25 SX has '''one 72-pin SIMM socket''' on the planar (in addition to soldered DRAM at U34 and optional sockets at U32/U33/U48/U49). The SIMM must be of an '''ECC parity''' type and must have the '''four presence-detect pins (67&ndash;70) configured for IBM size and speed encoding'''. Standard PC-style 72-pin parity SIMMs will not be recognised unless the presence-detect pins are tied to GND in the correct configuration.
== Keyboard and mouse ports ==


== Storage and Expansion ==
On the 8086 machine the keyboard and pointing-device interfaces are the same, so either device can go in either 6-pin connector at the rear.<ref name="tr25kb">IBM, ''IBM Personal System/2 Model 25 Technical Reference'', June 1987, "Keyboard and Pointing Device Controller", p. 1-8, hosted as [[IBM PS2 Model 25 Technical Reference (June 1987)]].</ref> The 286 and SX boards use an 8042 keyboard controller.<ref name="at286" /><ref name="atsx" /> The ports are fused on the system board: F1 and F2 on the Type 1 8086 board, a single F1 on the Type 2, 286 and SX boards.<ref name="at8525" /><ref name="at286" /><ref name="atsx" />


=== Expansion bus ===
== Power supply ==


* '''Model 25 (8086)''': two '''8-bit ISA''' expansion slots on a riser. The upper slot is partially obstructed by the CRT cage, preventing full-length cards from fitting; only the lower slot is fully usable for long cards.
The supply is inside the display assembly and powers the system unit, the display, options and keyboard.<ref name="tr25psu">IBM, ''IBM Personal System/2 Model 25 Technical Reference'', June 1987, section 3, "Power Supply", pp. 3-3 to 3-6, hosted as [[IBM PS2 Model 25 Technical Reference (June 1987)]].</ref> IBM's parts list has no separate supply: the display assembly is the FRU, with different part numbers for monochrome and colour, for the 8086, 286 and SX machines, and for mains region.<ref name="hmm" />
* '''Model 25 286''': two '''16-bit ISA''' slots on a riser, with an auxiliary 4-pin power connector for the 16-bit bus.
* '''Model 25 SX''': three '''16-bit ISA''' slots on a riser, with a fourth (flipside) slot used by the optional network card on the K01/L02 submodels.


=== Floppy interface ===
* Colour 8086 machines: 113 W, six voltage levels. System board: 7.0 A at +5 V, 1.7 A at +12 V, 100 mA at −5 V, 250 mA at −12 V. Display: 450 mA at 115 V DC and 220 mA at +12 V.
* Monochrome 8086 machines: 90 W, five voltage levels. The same system board outputs, plus 800 mA at +39 V DC for the display.<ref name="tr25psu" />
* Model 25 286 and Model 25 SX: 124.5 W, dual voltage, switched on the rear.<ref name="ann190082" /><ref name="ann192019" />


The Model 25 uses the '''PS/2 single-cable floppy interface''': power and data are carried in a single ribbon cable connecting the drive directly to the planar (no separate Molex 4-pin power lead). The interface is electrically different from PC/XT/AT 34-pin floppy interfaces. Drives are manufactured by ALPS, Mitsubishi, Sony, or YE-Data; Sony drives are the most likely to support 1.44 MB media on the original 8086 Model 25 even though it shipped only with 720 KB drives.
IBM Canada's quick reference gives 115 W for the colour 8086 machine; the Technical Reference gives 113 W.<ref name="qref25" /><ref name="tr25psu" /> The system board and drives take about 4 A of +5 V, leaving about 3 A for the two slots.<ref name="tr25psu" />


=== Hard drive interface ===
{| class="wikitable styled-table" style="width:90%; text-align:center;"
 
|+'''Model 25 (8086) DC outputs (Technical Reference Figures 3-2 and 3-3)'''
* The 8086 Model 25 has no hard drive support from IBM at launch. After-market kits used '''Seagate ST-506''' MFM drives in a 20 MB capacity, mounted in place of one of the floppy drives. The single-cable PS/2 interface includes the ST-506 lines.
! Rail !! Load !! Regulation !! Ripple !! Under-voltage sense
* The Model 25 286 supports a '''30 MB ST-506''' drive on the same single-cable interface (submodels 8525-036 / 8525-G36).
* The Model 25 SX uses standard '''40-pin IDE''' at J10, with hard drive power supplied through the planar.
 
=== Power supply ===
 
* '''Model 25 (8086) monochrome (001, C02)''' &mdash; 90 W IBM PS/2 power supply.
* '''Model 25 (8086) colour (004, C05)''' &mdash; 115 W IBM PS/2 power supply (higher current required by the colour CRT).
* Both are 110/220 VAC switchable.
* The PSU has '''no Molex 4-pin drive connectors'''; drive power is delivered through the planar via the same single-cable PS/2 interface as the data lines.
* '''The Model 30 PSU is not a drop-in replacement''' for the Model 25 PSU &mdash; the planar connectors and pinouts differ.
 
== Display ==
 
The Model 25 8086 uses '''MCGA''' (Multi-Color Graphics Array), the same video subsystem used on the Model 30 8086. MCGA is built into the planar and supports:
 
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''MCGA video modes (Model 25 8086)'''
! Mode !! Resolution !! Colours !! Refresh !! Notes
|-
| 0 / 1 || 40 × 25 text || 16 || 70 Hz || 8 × 16 character box
|-
|-
| 2 / 3 || 80 × 25 text || 16 || 70 Hz || 8 × 16 character box
| +5 V || 1.5 to 7.0 A || +5 % to −3 % || 100 mV p-p || +3.2 V
|-
|-
| 4 / 5 || 320 × 200 || 4 || 70 Hz || CGA-compatible
| −5 V || 0.0 to 0.11 A || +10 % to −8 % || 50 mV || −2.4 V
|-
|-
| 6 || 640 × 200 || 2 || 70 Hz || CGA-compatible
| +12 V || 0.12 to 1.7 A || +5 % to −3 % || 120 mV || +10.5 V
|-
|-
| 0x11 || 640 × 480 || 2 || 60 Hz || MCGA-specific (monochrome)
| −12 V || 0.015 to 0.25 A || +10 % to −8 % || 120 mV || −8.6 V
|-
| 0x13 || 320 × 200 || 256 || 70 Hz || MCGA-specific
|}
|}


The total displayable palette is '''262,144 colours''' (18-bit). On a monochrome 12" CRT, colours are summed to 64 shades of grey by the BIOS. MCGA is '''analog-only''' (RGB-A on a 15-pin VGA-style connector); it will not drive a CGA TTL digital monitor, and digital displays are not supported.
The Model 25 is an ISA machine and has a −5 V rail for adapters. The input is 115 V AC nominal (90 to 137 V, 2.0 A) or 230 V (180 to 265 V, 1.0 A), set by a switch on the rear, and is fused inside. The supply shuts down while an over-current or under-voltage condition exists. Power Good is 2.4 to 5.25 V when active, with a turn-on delay of 100 to 500 ms.<ref name="tr25psu" /> Power reaches the system board on the 12-pin J7: pin 1 Power Good, pins 2 and 5 to 8 ground, pin 3 +12 V, pin 4 −12 V, pin 9 −5 V, pins 10 to 12 +5 V.<ref name="tr25psu" /><ref name="hmm" /> A Model 30 supply does not fit.<ref name="dosdays" />
 
The Model 25 286 and Model 25 SX have '''VGA''' (Model 25 286) or '''Super VGA''' (Model 25 SX), driven on the same integrated 12" CRT and exposed through a standard 15-pin VGA connector on the rear of the system unit.
 
== Keyboard and Mouse ==


The Model 25 ships with either the '''IBM Space-Saving Keyboard''' (IBM P/N 1391472, 84-key Model M, no separate numeric keypad) or the '''IBM Enhanced Keyboard''' (IBM P/N 1391406, 101-key Model M). Both use the '''PS/2 keyboard protocol''' on a 6-pin Mini-DIN connector (the same connector used on PCs from 1996 onwards).
== Reference Diskette ==


The Model 25 also introduces the '''IBM PS/2 Pointing Device port''' &mdash; the connector that became known as the "PS/2 mouse port." The keyboard and mouse ports on the 8525 are functionally identical at the planar level (both connect through the 8042 keyboard controller); IBM identifies them only by a raised keyboard icon over the keyboard port. The two are interchangeable in software, but plugging a mouse into the keyboard socket and vice versa will produce a '''301 error''' at POST.
The Model 25 has no setup program in ROM. Configuration and diagnostics come from the model's own Reference or Starter Diskette; ardent-tool lists separate diskettes for the 8086, 286 and SX machines, and the SX has no Starter Disk and is configured with Advanced Diagnostics.<ref name="at8525" /><ref name="at286" /><ref name="atsx" /> Power on with the diskette in the drive: soft-booting it can cause false errors and a false report that a power-on password is set.<ref name="aterr">Ardent Tool of Capitalism, [https://www.ardent-tool.com/trouble/ps2error.html "PS/2 Error Codes"]. Reference Diskette use, multiple-error order, dead-system procedure and line-cord advice.</ref>


A '''3 A fuse''' (F1 on the planar) protects the combined +5 V supply to the keyboard and pointing device.
== Documentation ==


== ROM BIOS and Reference Diskette ==
* [[IBM PS2 Model 25 Technical Reference (June 1987)]]: the 8086 machine's hardware and BIOS reference.
* [[IBM Personal System 2 Hardware Maintenance Manual (S52G-9971-02, October 1994)]]: symptom-to-FRU index, system board locations and parts for the 8086, 286 and SX machines.
* IBM announcement letter 187-148, hosted as [[IBM Announcement Letter 187-148: PS/2 Model 25|IBM Announcement Letter 187-148: PS/2 Model 25]].


The PS/2 line uses '''two parallel BIOS layers''':
== General maintenance ==


* '''CBIOS''' (Compatible BIOS): backward-compatible with the PC/XT/AT BIOS, used by PC DOS.
Opening the machine, the display assembly hazards, rail checks and batteries are in [[IBM PS/2 Model 25 Maintenance Guide]].
* '''ABIOS''' (Advanced BIOS): the PS/2 protected-mode / multitasking-aware BIOS, used by OS/2.
 
The Model 25 BIOS is held in '''two 32 KB EPROMs''' (64 KB total) in sockets U13/U17 (or U19/U20 depending on planar revision). Unlike the PC/AT, the Model 25 does '''not''' have IBM ROM BASIC in the BIOS &mdash; instead, a stub in the BIOS prompts for a boot diskette if none is found.
 
The Model 25 does not have a built-in SETUP utility. All configuration is performed from the '''IBM Personal System/2 Reference Diskette''', a model-specific boot diskette supplied with the machine. The Reference Diskette includes:
 
* '''SETUP''' &mdash; sets memory size, drive types, date/time (286/SX only), display, mouse, and adapter card definitions.
* '''Advanced Diagnostics''' &mdash; full hardware test suite (entered with Ctrl-A from the main menu).
* '''Backup utilities''' for copying the Reference Diskette to a working diskette.
 
Reference Diskettes are '''model-specific'''. A 5170 Diagnostics diskette will not work on a Model 25; a Model 30 Reference Diskette is also '''not''' interchangeable with the Model 25 Reference Diskette.
 
Cold boots of the Reference Diskette are recommended over warm (Ctrl-Alt-Del) boots, because a warm boot may produce false errors or falsely indicate that a power-on password is already set.
 
== General Maintenance ==
 
CRT bezel removal, planar inspection, PSU rail checks, RTC battery replacement (Model 25 286 / 25 SX), keyboard / mouse port care and PS/2 single-cable connector care are documented in [[IBM PS/2 Model 25 Maintenance Guide]].


== Troubleshooting ==
== Troubleshooting ==


Power-on audio beep codes, the complete 1xx through 25xx PS/2 numeric POST error code listing, the dead-system isolation procedure, Reference Diskette use, ECA 082 system board recall, keyboard and PS/2 mouse port diagnostics, MCGA / VGA CRT diagnostics and PSU fault isolation are documented in [[IBM PS/2 Model 25 Troubleshooting Guide]].
IBM's symptom-to-FRU index, memory isolation, power checks and password removal are in [[IBM PS/2 Model 25 Troubleshooting Guide]].


== Capacitor Replacement ==
== Capacitor replacement ==


Tantalum failure on the Model 25 planar and electrolytic ageing in the Model 25 PSU and integrated CRT subsystem are documented in [[IBM PS/2 Model 25 Capacitor Replacement Guide]].
The diskette drive boards, the system board and the display assembly are covered in [[IBM PS/2 Model 25 Capacitor Replacement Guide]].


== Gallery ==
== Gallery ==
<gallery mode="packed" heights="220">
<gallery mode="packed" heights="220">
File:IBM PS2 Model 25 product photo.png|IBM PS/2 Model 25 (early Type 1 product photo)
File:IBM PS2 Model 25 product photo.png|IBM PS/2 Model 25
File:IBM PS2 Model 25 front.jpg|IBM PS/2 Model 25 front view (Museo de Informática)
File:IBM PS2 Model 25 front.jpg|Front view
File:IBM PS2 Model 25 angle.jpg|IBM PS/2 Model 25 angled view (Museo de Informática)
File:IBM PS2 Model 25 angle.jpg|Angled view
File:IBM PS2 Model 25 SX.jpg|IBM PS/2 Model 25 SX (Intel 386SX, sold to schools)
File:IBM PS2 Model 25 SX.jpg|Model 25 SX
File:IBM PS2 Model 25 8086 badge.svg|Front-panel badge from the 8086 Model 25
File:IBM PS2 Model 25 8086 badge.svg|Model 25 badge
File:IBM PS2 Model 25 286 badge.svg|Front-panel badge from the Model 25 286
File:IBM PS2 Model 25 286 badge.svg|Model 25 286 badge
</gallery>
</gallery>


== Related Pages ==
== References ==
 
<references />
 
== Related pages ==


* [[IBM PS/2 Model 25 Maintenance Guide]]
* [[IBM PS/2 Model 25 Maintenance Guide]]
* [[IBM PS/2 Model 25 Troubleshooting Guide]]
* [[IBM PS/2 Model 25 Troubleshooting Guide]]
* [[IBM PS/2 Model 25 Capacitor Replacement Guide]]
* [[IBM PS/2 Model 25 Capacitor Replacement Guide]]
* [[IBM PC AT (5170)]] &mdash; preceding business-class generation
* [[IBM PS/2 Model 30]]
* [[IBM PC XT (5160)]] &mdash; preceding entry-level
* [[IBM PCjr]]
* [[IBM PCjr]] &mdash; preceding consumer attempt
 
== References ==
 
* [https://en.wikipedia.org/wiki/IBM_PS/2_Model_25 IBM PS/2 Model 25 &mdash; Wikipedia]. Source for release/withdrawal dates, model line history, submodel list, MCGA/VGA video distinction.
* [https://www.dosdays.co.uk/computers/IBM%20PS2%20Model%2025/ibm_ps2_model_25.php IBM PS/2 Model 25 &mdash; DOS Days]. Source for submodel pricing, planar IC layout, PSU wattage, hard drive options, BIOS layout (two 32 KB EPROMs in U19/U20), and proprietary memory pinouts.
* [https://www.ardent-tool.com/qtechinfo/8525.html IBM Canada Ltd Quick Reference &mdash; PS/2 Model 25 (8525)]. IBM-supplied technical reference: machine type, announce date, list price ($2,095 / $2,595), microprocessor and clock, BUS, ports, memory, PSU wattage and weight (12.7 kg mono / 16.8 kg colour), dimensions (382 × 320 × 375 mm), MCGA modes, configurations and options.
* [https://www.ardent-tool.com/qtechinfo/8525-286.html IBM Canada Ltd Quick Reference &mdash; PS/2 Model 25 286]. Source for the Model 25 286 chipset (VLSI VL82C100&ndash;104), wait-state count, ISA 16-bit slot count, hard drive option, BIOS/RTC battery.
* IBM, ''IBM Personal System/2 and IBM Personal Computer Product Reference, Version 4.0'' (September 1988). Source for the submodel table.
* [https://www.ardent-tool.com/trouble/ps2error.html PS/2 Error Codes], Ardent Tool of Capitalism. Reference for the PS/2 error code organisation (Major Error / Minor Diagnostic Error, the 4 + 4 format used on the Premium Line LED panel).


{{Navbox-IBMComputers|state=expanded}}
{{Navbox-IBMComputers|state=collapsed}}


[[Category:IBM]]
[[Category:IBM]]

Latest revision as of 18:19, 1 October 2026

IBM Personal System/2 Model 25
IBM PS/2 Model 25 (8525)
Specifications
ManufacturerIBM
TypeAll-in-one personal computer
Released4 August 1987 (Model 25); 1 June 1990 (Model 25 286); 17 April 1992 (Model 25 SX)
Intro priceUS$1,350 (8525-001) to US$1,740 (8525-G04) at launch
CPUIntel 8086 at 8 MHz, no wait states; 80286 at 10 MHz (Model 25 286); 386SX at 16 MHz (Model 25 SX)
Memory512 KB, 640 KB maximum on the system board (8086); 0.5 to 4 MB on the board (286); 1 or 4 MB, 16 MB maximum (SX)
StorageOne or two 3.5-inch diskette drives (720 KB on the 8086, 1.44 MB on the 286 and SX); optional fixed disk
DisplayIntegrated 12-inch analogue display, monochrome or colour; MCGA (8086), VGA (286 and SX)
SoundBeeper; earphone connector
Dimensions382 × 320 × 375 mm (H × W × D)
Weight14.1 kg monochrome, 16.3 kg colour (8086, IBM US); 16.0 to 17.7 kg (286 and SX)
OS / FirmwareIBM PC DOS 3.30 and later; DOS 5.0 shipped with the SX
PredecessorIBM PC (5150), IBM PC XT (5160)
Model no.8525

The IBM Personal System/2 Model 25 (machine type 8525) is the all-in-one member of IBM's PS/2 range: the system board, drives and supply share one case with a 12-inch display. IBM announced it on 4 August 1987 as a low-priced machine running at about twice the speed of the 8088-based IBM PCs, with an 8086 at 8 MHz, MCGA graphics and two slots for existing PC and XT cards.[1] Like the Model 30 it has ISA slots; IBM kept Micro Channel for the higher models.[2] IBM later sold a Model 25 286 (1990) and a Model 25 SX for schools (1992).

History

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The first four models, 001 and G01 (monochrome) and 004 and G04 (colour), were priced at US$1,350, $1,395, $1,695 and $1,740. The 001 and 004 were available on the day of announcement and the G models, with the Enhanced Keyboard instead of the Space Saving Keyboard, from 30 October 1987.[1] IBM Canada listed the 001 and 004 at $2,095 and $2,595.[3]

The Model 25 LS (8525-L01 monochrome and L04 colour), announced on 2 June 1988, came with 640 KB, the Enhanced Keyboard and an IBM Token-Ring Network PC Adapter, at US$2,139 and $2,484 through dealers.[4]

The Model 25 286 (8525-006, G06, 036, G36) was announced on 10 May 1990 for availability on 1 June 1990. It has an 80286 at 10 MHz with one wait state, 0.5 or 1 MB on the system board expandable to 4 MB, 1.44 MB diskette support and VGA, and the 036 and G36 have a 30 MB fixed disk. Prices ran from US$2,295 to $3,040. IBM noted that the new drive options announced with it do not fit earlier 8525 models.[5]

The Model 25 SX (8525-K00, K01, L02) was announced on 21 January 1992, available from 17 April 1992, and sold through IBM's K-12 education channels only. It has a 386SX at 16 MHz, 1 MB (K00) or 4 MB (K01, L02) of parity memory with a 16 MB maximum, VGA with 256-colour support, and DOS 5.0. The K01 adds an Ethernet adapter and the L02 a Token-Ring adapter, both with Remote Initial Program Load. Prices were US$2,082, $2,832 and $3,165.[6]

Models

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IBM PS/2 Model 25 models (IBM US announcement letters)
Model Processor Memory as shipped Storage Display Notes
8525-001, G01 8086, 8 MHz 512 KB One 720 KB diskette Monochrome G01 has the Enhanced Keyboard
8525-004, G04 8086, 8 MHz 512 KB One 720 KB diskette Colour G04 has the Enhanced Keyboard
8525-L01, L04 8086, 8 MHz 640 KB One 720 KB diskette Monochrome / colour Model 25 LS, Token-Ring adapter fitted
8525-006, G06 80286, 10 MHz 512 KB One 1.44 MB diskette Colour VGA Model 25 286
8525-036, G36 80286, 10 MHz 1 MB 1.44 MB diskette, 30 MB fixed disk Colour VGA Model 25 286
8525-K00 386SX, 16 MHz 1 MB One 1.44 MB diskette Colour VGA Model 25 SX, education only
8525-K01, L02 386SX, 16 MHz 4 MB One 1.44 MB diskette Colour VGA Ethernet (K01) or Token-Ring (L02)

Sources: 187-148, 188-081, 190-082 and 192-019.[1][4][5][6]

Architecture

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Model 25 (8086) system board

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There are three system boards: Type 1 (P/N 00F2073), Type 2 (FRU P/N 96F7390, P/N 64F0738) and a Japanese board (P/N 78X8943) made by Panasonic/Matsushita. The layouts differ, but the reference designators are largely the same across all of them and across the 8086 Model 30 boards.[7] IBM's 1994 maintenance manual lists 96F7390 as the system board FRU.[8]

Model 25 (8086) system board, principal parts (ardent-tool)
Designator Part
U10 Intel 8086-2 CPU, 8 MHz
U13 8087 coprocessor socket
U8 Intel P8253-5 timer
U9, U11, U12, U14, U15 IBM gate arrays 72X8203, 72X8300 (MCGA memory controller), 72X8205 (MCGA video formatter), 72X8206, 72X8202
U5 IMSG171P RAMDAC
U6, U7 HM53461P 64K × 4 DRAM (MCGA)
U38 CXK5864BM-12L 8K × 8 SRAM (MCGA)
U16, U22, U34, U35 NEC D4164C-10 DRAM
ZM1, ZM2 MSM3764A-15 64K × 1 DRAM
U18 µPD765AC-2 diskette controller
U19 8237A DMA controller
U27 NS8250AV UART
F1, F2 Fuses, probably mouse and keyboard (combined in F1 on the Type 2 board)
J7 Power connector
J8 Fan connector
J9 Memory (dual 30-pin sockets)
J11 44-pin fixed-disk connector
J12 40-pin diskette connector
Y1, Y2, Y3 14.31818 MHz, 25.175 MHz and 48.0 MHz oscillators

The 8086 Model 25 has no real-time clock: its BIOS system descriptor reports "No Real-time clock",[9] and it is the only PS/2 without a CMOS battery.[10] The riser card (P/N 78X9031) carries two 8-bit ISA slots and a resistor pack.[7] The Model 25 does not use the same power connector as the 8086 Model 30.[7]

Model 25 286 system board

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The board (ardent-tool gives FRU P/N 64F0178, P/N 37F6675; IBM's 1994 manual lists FRU 96F7435) uses the VLSI VL82CPCAT chipset at ZM2 to ZM6, a 286-10 at ZM36 and a 287 socket at ZM1. Other parts: VL16C451 serial and parallel at ZM9, 27F4094 diskette gate array at ZM14, 15F6864 VGA controller at ZM18 with an IMSG171P-35 RAMDAC at ZM23, µPD765BC diskette controller at ZM19, 8042 keyboard controller at ZM33 and a Dallas DS1287 clock module at ZM35. Memory is 30-pin SIMMs with parity in J9 and J10. J13 is the password-override connector, and J7 and J14 are the power connectors.[11][8]

Model 25 SX system board

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The board (ardent-tool gives FRU P/N 87F4769 in "K" and "L" versions; IBM's 1994 manual lists 42G2802 with 1 MB and 42G2803 with 4 MB) has an i386SX at U2, clocked at 16 MHz from a 32 MHz oscillator; many are 20 MHz parts run at 16 MHz. The chipset is a VLSI VL82C304 and VL82C305, with an 8042 keyboard controller at U10, an 82077AA diskette controller at U25, ROM BIOS 87F4794 at U26, and IBM's 84F7985 SVGA controller at U42 with its own video RAM. Memory is soldered 512K × 9 DRAM plus one 72-pin SIMM socket at J6; J4 is an unfitted second socket. J10 is a 40-pin IDE connector, J14 a 4-pin hard-disk power connector, J2 the power-on password clear, and B1 a CR2032 cell for the clock, with a 32.768 kHz crystal at Y1.[12][8] IBM's announcement mentions VGA only; the controller's SVGA modes work with IBM's VESA driver, though the built-in display cannot sync to 800 × 600.[6][12]

Storage

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Each diskette drive takes power and data through one cable from the system board; there is no separate drive power lead.[2] PS/2 diskette drives were made mostly by Alps and Mitsubishi, with Sony and YE-Data less common.[2] The 8086 machine shipped with 720 KB drives but has undocumented 1.44 MB support that works reliably only with Sony drives, and later system boards accept more drives than early ones.[7]

PS/2 3.5-inch drives are direct drive: Mitsubishi's MF355C specification describes a brushless DC motor turning the spindle directly at 300 rpm.[13]

The Model 25 has no hard-disk controller on the system board. IBM describes its 44-pin fixed-disk connector as "a dedicated I/O channel for the connection of the IBM Personal System/2 20MB Fixed Disk Drive and controller, or similar attachment", carrying ordinary I/O-channel signals, a −DISK CS select decoded at hex 032x, a −Disk Installed line and address lines A0 to A2 to pick a register in the drive's controller.[14] The Model 25 SX is the only Model 25 with a 40-pin IDE connector.[12]

Display

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The 8086 Model 25 has MCGA on the system board with a 64 KB display buffer. It supports the CGA modes plus 640 × 480 in 2 colours, 320 × 200 in 256 colours, and 40- and 80-column text in 16 colours with an 8 × 16 character box, all from 262,144 colours. It does not support the 640 × 350 mode or mode 7 for the IBM 5151 monochrome display. On the monochrome models the MCGA converts colour to up to 64 shades of grey.[1] The palette has 256 18-bit registers driving three 6-bit DACs.[15] The Model 25 286 has VGA, and the Model 25 SX VGA with IBM's SVGA controller.[5][12]

Keyboard and mouse ports

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On the 8086 machine the keyboard and pointing-device interfaces are the same, so either device can go in either 6-pin connector at the rear.[16] The 286 and SX boards use an 8042 keyboard controller.[11][12] The ports are fused on the system board: F1 and F2 on the Type 1 8086 board, a single F1 on the Type 2, 286 and SX boards.[7][11][12]

Power supply

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The supply is inside the display assembly and powers the system unit, the display, options and keyboard.[17] IBM's parts list has no separate supply: the display assembly is the FRU, with different part numbers for monochrome and colour, for the 8086, 286 and SX machines, and for mains region.[8]

  • Colour 8086 machines: 113 W, six voltage levels. System board: 7.0 A at +5 V, 1.7 A at +12 V, 100 mA at −5 V, 250 mA at −12 V. Display: 450 mA at 115 V DC and 220 mA at +12 V.
  • Monochrome 8086 machines: 90 W, five voltage levels. The same system board outputs, plus 800 mA at +39 V DC for the display.[17]
  • Model 25 286 and Model 25 SX: 124.5 W, dual voltage, switched on the rear.[5][6]

IBM Canada's quick reference gives 115 W for the colour 8086 machine; the Technical Reference gives 113 W.[3][17] The system board and drives take about 4 A of +5 V, leaving about 3 A for the two slots.[17]

Model 25 (8086) DC outputs (Technical Reference Figures 3-2 and 3-3)
Rail Load Regulation Ripple Under-voltage sense
+5 V 1.5 to 7.0 A +5 % to −3 % 100 mV p-p +3.2 V
−5 V 0.0 to 0.11 A +10 % to −8 % 50 mV −2.4 V
+12 V 0.12 to 1.7 A +5 % to −3 % 120 mV +10.5 V
−12 V 0.015 to 0.25 A +10 % to −8 % 120 mV −8.6 V

The Model 25 is an ISA machine and has a −5 V rail for adapters. The input is 115 V AC nominal (90 to 137 V, 2.0 A) or 230 V (180 to 265 V, 1.0 A), set by a switch on the rear, and is fused inside. The supply shuts down while an over-current or under-voltage condition exists. Power Good is 2.4 to 5.25 V when active, with a turn-on delay of 100 to 500 ms.[17] Power reaches the system board on the 12-pin J7: pin 1 Power Good, pins 2 and 5 to 8 ground, pin 3 +12 V, pin 4 −12 V, pin 9 −5 V, pins 10 to 12 +5 V.[17][8] A Model 30 supply does not fit.[2]

Reference Diskette

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The Model 25 has no setup program in ROM. Configuration and diagnostics come from the model's own Reference or Starter Diskette; ardent-tool lists separate diskettes for the 8086, 286 and SX machines, and the SX has no Starter Disk and is configured with Advanced Diagnostics.[7][11][12] Power on with the diskette in the drive: soft-booting it can cause false errors and a false report that a power-on password is set.[18]

Documentation

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General maintenance

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Opening the machine, the display assembly hazards, rail checks and batteries are in IBM PS/2 Model 25 Maintenance Guide.

Troubleshooting

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IBM's symptom-to-FRU index, memory isolation, power checks and password removal are in IBM PS/2 Model 25 Troubleshooting Guide.

Capacitor replacement

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The diskette drive boards, the system board and the display assembly are covered in IBM PS/2 Model 25 Capacitor Replacement Guide.

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  • IBM PS/2 Model 25
    IBM PS/2 Model 25
  • Front view
    Front view
  • Angled view
    Angled view
  • Model 25 SX
    Model 25 SX
  • Model 25 badge
    Model 25 badge
  • Model 25 286 badge
    Model 25 286 badge

References

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  1. ↑ 1.0 1.1 1.2 1.3 IBM, Announcement Letter 187-148, "IBM 8525, Personal System/2 Model 25", 4 August 1987, hosted as File:IBM Announcement Letter 187-148 PS2 Model 25 (August 1987).pdf. Description, standard features, prices, availability dates, physical specifications, universal power supply and compatibility notes.
  2. ↑ 2.0 2.1 2.2 2.3 DOS Days, "IBM PS/2 Model 25". Community reference: drive cabling, drive makers, dust shutters and capacitor leakage, 1.44 MB support with Sony drives, and the Model 30 supply not fitting.
  3. ↑ 3.0 3.1 IBM Canada Ltd, Quick Reference, "IBM Personal System/2 Model 25", transcribed at ardent-tool.com. Canadian prices, memory type, weights, supply ratings and MCGA summary.
  4. ↑ 4.0 4.1 IBM, Announcement Letter 188-081, "IBM Personal System/2 Model 25 LS", 2 June 1988, transcribed at ardent-tool.com.
  5. ↑ 5.0 5.1 5.2 5.3 IBM, Announcement Letter 190-082, "IBM Personal System/2 Model 25 286 (8525-006, G06, 036, G36)", 10 May 1990, transcribed at ardent-tool.com. Features, prices, 124.5 W supply, weights, BTU output and DOS support.
  6. ↑ 6.0 6.1 6.2 6.3 IBM, Announcement Letter 192-019, "IBM Personal System/2 Model 25 SX (8525-K00, K01, L02)", 21 January 1992, transcribed at ardent-tool.com. Features, prices, memory, LAN models, 124.5 W supply, dimensions and weight.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Ardent Tool of Capitalism, "8525 Planar", based on content by William R. Walsh. Designator lists for the Type 1, Type 2 and Japanese boards, ROM images, riser card, MCGA notes, power connector, diskette drive notes and ECA 023.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 IBM, Personal System/2 Hardware Maintenance Manual, S52G-9971-02, October 1994, hosted as IBM Personal System 2 Hardware Maintenance Manual (S52G-9971-02, October 1994). General Checkout and Symptom-to-FRU Index (AT Bus), pp. 3 to 17; power supply connector, p. 138; system board locations, pp. 185 to 188; Model 25 parts, pp. 223 to 225.
  9. ↑ IBM, IBM Personal System/2 Model 25 Technical Reference, June 1987, p. 5-45, hosted as IBM PS2 Model 25 Technical Reference (June 1987).
  10. ↑ Ardent Tool of Capitalism, "PS/2 RTC/CMOS Batteries", based on content by Bob Eager and Peter H. Wendt. Battery type and FRU for each model, DS1287 replacements, CR2032 test limits.
  11. ↑ 11.0 11.1 11.2 11.3 Ardent Tool of Capitalism, "8525-286 Planar". Designator list, ROM images, memory, earphone connector board and memory expansion address table.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 Ardent Tool of Capitalism, "8525 SX Planar", based on content by William R. Walsh. Designator lists for the K and L boards, ROM image, unpopulated memory positions, the riser slot for the LAN adapter, the SVGA controller and the CPU speed.
  13. ↑ Mitsubishi Electric, 3.5 inch Flexible Disk Drive Standard Specifications, MF355C, UGD-0527A, February 1987, section 3, hosted as File:Mitsubishi MF355C 3.5 inch Diskette Drive Specifications (UGD-0527A, Feb 1987).pdf.
  14. ↑ IBM, IBM Personal System/2 Model 25 Technical Reference, June 1987, "Fixed Disk Connector", p. 1-104, hosted as IBM PS2 Model 25 Technical Reference (June 1987).
  15. ↑ IBM, IBM Personal System/2 Model 25 Technical Reference, June 1987, video subsystem, pp. 1-36 and 1-57, hosted as IBM PS2 Model 25 Technical Reference (June 1987).
  16. ↑ IBM, IBM Personal System/2 Model 25 Technical Reference, June 1987, "Keyboard and Pointing Device Controller", p. 1-8, hosted as IBM PS2 Model 25 Technical Reference (June 1987).
  17. ↑ 17.0 17.1 17.2 17.3 17.4 17.5 IBM, IBM Personal System/2 Model 25 Technical Reference, June 1987, section 3, "Power Supply", pp. 3-3 to 3-6, hosted as IBM PS2 Model 25 Technical Reference (June 1987).
  18. ↑ Ardent Tool of Capitalism, "PS/2 Error Codes". Reference Diskette use, multiple-error order, dead-system procedure and line-cord advice.
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