The 661-6594 is compatible with:
MacBook Pro 13.3" 2.26GHz Core 2 Duo (A1278) - Mid 2009 MB990LL/A SKU177021
MacBook Pro 13.3" 2.4GHz Core 2 Duo (A1278) - Mid 2010 MC374LL/A SKU177022
GS177022
MacBook Pro 13.3" 2.53GHz Core 2 Duo (A1278) - Mid 2009 MB991LL/A SKU177021
MacBook Pro 13.3" 2.5GHz Core i5 (A1278) - Mid 2012 MD101LL/A SKU177023
MacBook Pro 13.3" 2.66GHz Core 2 Duo (A1278) - Mid 2010 MC375LL/A SKU177022
GS177022
MacBook Pro 13.3" 2.9GHz Core i7 (A1278) - Mid 2012 MD102LL/A SKU177023
The 661-5868 is compatible with:
MacBook Pro 13.3" 2.3GHz Core i5 (A1278) - Early 2011 MC700LL/A SKU22575
GS22575
GS22575B
MacBook Pro 13.3" 2.4GHz Core i5 (A1278) - Late 2011 MD313LL/A SKU22575
GS22575
GS22575B
MacBook Pro 13.3" 2.7GHz Core i7 (A1278) - Early 2011 MC724LL/A SKU22575
GS22575
GS22575B
MacBook Pro 13.3" 2.8GHz Core i7 (A1278) - Late 2011 MD314LL/A SKU22575
GS22575
GS22575B
Give us the last three figures of your serial number and we can tell which machine you have, located on the back of the machine in fine print.