Computer device in fashion, foremost from Microsoft (5)
I believe the answer is:
modem
'computer device' is the definition.
(short for modulator-demodulator)
'fashion foremost from microsoft' is the wordplay.
'fashion' becomes 'mode' (synonyms).
'foremost from' indicates taking the first letters (the letter at the front).
The first letter of 'microsoft' is 'm'.
'mode'+'m'='MODEM'
'in' acts as a link.
(Other definitions for modem that I've seen before include "Computer communication device" , "Phone line and computer connector" , "Connector for computer to telephone line" , "PC/telephone link" , "Device linking computers via a telephone line" .)