Difference b/w ULN2003 & ULN2001 transistor arrays

Does anyone know what the differences are, if any, between the ULN2001 and ULN2003 transistor arrays? I need a transistor array for my unipolar stepper motor driver circuit which must include a transistor array IC. The textbook mentions on pg. 6-27 to use a ULN2003 in conjunction with a buffer array, but the project kit contains a ULN2001 instead. I'm just wondering if they can be used interchangeably. Thanks!