Sun Microsystems Inc., a computer maker, announced the effectiveness of its registration statement for $125 million of 6 3/8% convertible subordinated debentures due Oct. 15, 1999. 

The company said the debentures are being issued at an issue price of $849 for each $1,000 principal amount and are convertible at any time prior to maturity at a conversion price of $25 a share. 

The debentures are available through Goldman, Sachs & Co.