UMC UM82C481

A 386DX/486 motherboard acquired from an auction, with information, repairs, testing and benchmarks.

[Update 12/02/2021] - The seller lost the motherboard, so this particular transaction wasn't completed.

The UMC UM82C481 seems to be a design from the middle of the 386 era; it has a compact chipset, but not quite the 1-chip solution of the very last boards, it has 8x 30pin SIMM sockets, sockets for up to 256KBytes of cache as well as the later, compact, PLCC version of the AMD 386DX-40. It would have been one of the better 386 designs that you could have bought at the time.

I got this board from a Russian-language auction site ( in early February 2021 for a very reasonable amount of money. One of the reasons being that it had obvious damage…

Items to note:

  • The battery has leaked, but appears to be relatively contained
  • Battery leak: on AT keyboard socket; needs to be desoldered and replaced
  • Battery leak: on BIOS rom socket; needs to be desoldered and replaced, and EPROM cleaned (and backed up, preferably)
  • Battery leak: around keyboard controller ; needs to be desoldered and cleaned
  • Battery leak: possible evidence on first ISA slot
  • Fitted with 4x Winbond W2457AK-20 SRAM chips 32kbx8 and 1x Motorola 8kbx8-15 tag SRAM, should be a total of 128KB of cache
  • Soldered-on AMD 80386DX-40 processor
  • Empty FPU socket

A summary of the motherboard capabilities follows:

Form Factor Baby AT
Chipset UMV UM82C481 / UMC82C482
Maximum RAM 8x 30pin SIMM; unknown capacity, but presumably 8x4MB to make 32MB
Cache Yes; unknown capacity
FPU Yes, PGA socket; 387
CPU Type 386 DX, PGA socket
CPU Speeds 25,33,40MHz
Expansion 6x16bit, 1x8bit

The UMC82C481 memory controller as fitted to this board supports the provision of UMB memory via The Last Byte memory manager. As noted in the file chipset.doc:

The following chip provides 256k of memory in eight 16k blocks
between C0000-DFFFF and two 64k blocks between E0000-FFFFF.

- UM82C481 - From the UM82C480 50Mhz 80486 Chip Set

These UMB regions can then be used to load drivers and TSR's high, using the highdvr and hightsr utility included with The Last Byte memory manager similar to the MS-DOS commands devicehigh and loadhigh.

Configuration 0

Test Config 0
Processor Speed MHz
Wait states 1
Norton Sysinfo CPU
Norton Sysinfo HDD
Norton Sysinfo Overall
CheckIt Dhrystones
CheckIt Whetstones
CheckIt Video chars/sec VGA 1
CheckIt Video chars/sec VGA 2
CheckIt HDD Transfer
Landmark CPU
Landmark FPU
Landmark Video VGA 1
Landmark Video VGA 2
3DBench VGA 1
3DBench VGA 2
ATPerf RAM Read
ATPerf RAM Write
ATPerf ROM Read
ATPerf Video Write VGA 1
ATPerf Video Write VGA 2
CompTest RAM thruput
CompTest Effective WS
CompTest Video BIOS VGA 1
CompTest Video BIOS VGA 2
CompTest Video Direct VGA 1
CompTest Video Direct VGA 2
CompTest Dhrystones

Games Results

In addition, the following game benchmark results were recorded:

Test Config 0
Wolfenstein 3D (FPS)
F1GP Bench 1 (CPU %)

Software Versions

  • Norton Sysinfo 8.0
  • CheckIt 2.1
  • Landmark 6.00
  • 3DBench 1.0
  • ATPerf 2.00
  • Comptest 260


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  • blog/386_shootout_umc.txt
  • Last modified: 2021/02/18 12:43
  • by john