Unisys 4253sx

Type MPI 42532 FDD
Serial 430054312
Manufacturer Unisys Corp., USA
Date April 1993 (MFG date on serial sticker 4/93)

Physical description

Type Desktop
Dimensions (HxWxD) 108 x 380 x 405 mm
Drive bays 2 x 3.5" (1 x half-height internal, 1 x slim), 1 x 5.25" half-height
Power supply 133 W, 100-127/200-240 V, 5/2.5 A, manual voltage switch (9306)

Main Board

Manufacturer Unisys (sticker 03/’93)
BIOS Award Modular BIOS v4.20, 18/8/90 (Unisys ISA BIOS 4 25/33/66 R1.144U), 49 Kb
Chipset VIA VT82C481, VT82C495
Processor Intel 80486SX-25 MHz (32-bit), PGA
Coprocessor N/a (CPU can be replaced with a 486DX/DX2 up to 33/66 MHz)
Memory 4 sockets for 72-pin SIMMs (*)
Max on system board 64 Mb (4 x 16 Mb)
External cache 256 Kb ADDITION
Bus ISA 16-bit
Expansion slots 3 x 16-bit ISA (on riser card), all available
Video Integrated Super-VGA display adapter (S3 86C805)
Interface Integrated SCSI (Adaptec ASW-B626 - chip Adaptec AIC-6260AL), FDD (2 units)
Ports PS/2 keyboard, PS/2 mouse, 2 serial (UART 16450), parallel, VGA, SCSI


Installed RAM 4 x 4 Mb 80ns SIMMs (9347 on chips, 9444, two 9313 on card)
Ethernet SMC 8013EWC (1393) ADDITION


Diskette drive 1.44 Mb, 3.5" slim (Sony MFD-17W, 92-06)
Hard disk Quantum ProDrive ELS-85S (85 Mb) SCSI, 3.5" slim


Acquisition Sept. 99, bought together w. some other appliances incl. two 7033 monitors, two 4336 system units and a second 4253 (later demolished to get spare parts), everything was paid a few $
Condition Very good, working
Installed O.S. MS-DOS 6.20, MS Windows for Workgroup 3.11 (Italian)
Modifications Added two 4 Mb memory SIMMs (it had 8 Mb) and 256 Kb cache
Current status All hw working
Current O.S. MS-DOS 6.0 (US English), MS Windows 3.1 (Italian)
Spare parts Enough to build a second machine, most parts had been tested and are OK


(*) apparently, only accepts single-bank SIMMs (1, 4 or 16 Mb).

Peripherals: MONITORS

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This page was first published on the web on Nov. 11, 2001
Last revised May 24, 2004