Epson 20 - Manual (Page 171)

When you select a check from this menu, the program determines the
number of hard disk drives installed in your computer. If you have
more than one physical drive, then each time you select a test you see
this prompt:
Check which drive (C/D)?
Press C or D and then Enter.
Seek Check
This test checks the ability of the read/write heads to locate any part
of the hard disk. This action by a read/write head is called a seek.
During this test, each head seeks each cylinder of the disk in
sequence, starting from the center.
Select option 1 from the menu to start this test. The program displays
the number of each cylinder it finds. For example, with a hard disk,
the first message you see is:
Current cylinder is nnn
where nnn is the largest cylinder number used on the drive. The
cylinder number counts down to 0. The seek is performed by the
read/write heads simultaneously, so you see the cylinder numbers
only once. If no errors occur, the menu reappears.
Write, Read Check
This check tests the ability of the hard disk drive to read and write
data. The test writes to and reads from each sector of the innermost
cylinder of the disk, using each head.
Performing System Diagnostics C-27