An ASR set consists of a system backup and a 3.5" disk that lists the system files that are installed on the PC. If you don't have a 3.5" disk drive on your machine, you won't be able to create the ASR disk. However, you can still create an ASR disk by performing the following steps:
1. Run the ASR wizard, which is part of Windows Backup.
2. After you run the ASR Wizard, start Windows Explorer.
3. Navigate to the \%windir%\repair folder (e.g., C:\windows\repair).
4. Copy the asr.sif and asrpnp.sif files to a network location.
5. On a different networked computer that has a 3.5" disk drive, copy these files to a 3.5" disk and label the disk as your ASR disk.
For more information on ASR backup read this article : http://tec-articles.blogspot.com/2007/10/taking-automated-system-recovery-asr.html