How to change drives in MS-DOS and Windows command line
To change the drive letter in MS-DOS, type the drive letter followed by a colon. For example, if you wanted to switch to the floppy disk drive, you would type a: at the prompt. Below is a listing of common drive letters and their corresponding devices.
Tip: A partition is also treated as a drive, which means if you have a hard drive with two partitions, it is likely the C: and D: drive letters.
Floppy disk drive (commonly the 3.5" floppy drive).
A second floppy disk drive, if present (commonly the 5.25" floppy drive).
Commonly the CD-ROM drive or another drive unless the computer hard drive has multiple partitions. If multiple partitions exist, your CD-ROM drive is the last letter. For example, if one extended partition exists, your CD-ROM drive will be the E: drive because the hard drive partitions would use C: and D: drive letters.
Accessing a USB drive
To access a USB thumb drive or external drive you must know what drive letter the computer has assigned to the drive. For example, if the USB is assigned to the F: drive you can type f: at the prompt to switch to the F: drive.
What happens after switching drives?
The system cannot find the drive specified.
If this occurs and you know the drive exists, it is likely that your drive is having problems.
If the drive and drive letter do exist but there is no media to read then you'll get the below error.
The device is not ready.
For example, the above error will be received if you switch the floppy disk drive with no diskette in the drive or a CD-ROM or DVD drive with no disc in the drive or a disc that cannot be read.
Tip: If you just want to list the files on an alternate drive you can also type dir followed by the drive letter. For example, "dir a:" will list the files on the floppy drive but will not switch your prompt to the floppy drive.