According to Official Guinness Records,
The world's largest PC DIY assembly consisted of 1,912 participants building 961 working personal computers on 1 October 2003. The event took place at Shek Kip Mei Park Sports Centre of Sham Shui Po District, Hong Kong, China.
The event lasted for 1 hr 19 min.
For a complete list of 2003 records, please visit 2003 Guinness Records in China.