Uploaded October 2024 | Updated September 2026, 2 weeks ago

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Assembly language, HEX editor, checksums! This video has it all! I received enough feedback from my audience to attempt reverse-engineering the fake cache BIOS of my 486 BEK-tronic BEK-V429S motherboard. Will we be able to patch and revert the change scammers have introduced in the BIOS to always display 256K L2 cache regardless if or what cache chips are installed?

Link to the Excel sheet and post: bitsundbolts.com/2024/10/25/patching-a-bios-to-fix-a-a-fake-cache-size-display

Disassembled offending code: gist.github.com/tostercx/f6fb1e486d8d89b021993e3bbba27282

The new BIOS is already listed on The Retro Web:
theretroweb.com/motherboards/s/bek-tronic-bek-v429s#bios

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▬▬▬▬ *Timestamps* ▬▬▬▬▬▬▬▬▬▬▬▬▬▬
00:00 The fake cache motherboard/BIOS
02:37 Preparation
03:56 BIOS 2.01r: Find the cache calculation
10:05 BIOS 1.2: Find the cache calculation
12:29 Find the difference: 2.01r vs 1.2
16:32 BIOS 1.2: The good code
21:54 BIOS 2.01r: The bad code
27:55 Possible fixes
28:49 How to get 32MB of L2 cache
33:13 Checksum errors
36:46 Patch the BIOS code
42:00 Testing the fixed BIOS