Modern 3½" 640MB MO drives are fast enough to be used as general storage or like a hard disk. However, writes are slower than reads, and if you are planning on using an MO disk for very write-intensive applications, you should probably use LIMDOW media to speed up writes. For general backup, file storage and running applications & games from, normal non-LIMDOW disks are fine. Note that the seek time will not be as quick as most modern hard disks.

Figures for Fujitsu's current 640MB 3½" MO drive mechanisms are as follows:

+--------------------+------------+-----------+-----------+-----------+
|Storage Capacity    |    128MB   |   230MB   |   540MB   |   640MB   |
|--------------------+------------+-----------+-----------+-----------|
|Sector size (bytes) |                 512                |   2048    |
|--------------------+------------+-----------+-----------+-----------|
|Transfer Rate (max) |            |           |                       |
| 3600rpm (MCB3064SS)|  1.09MB/s  |1.3-2.1MB/s|      2.3-3.9MB/s      |
| 4300rpm (MCB3064SS)|  1.3MB/s   |1.6-2.5MB/s|      2.8-4.7MB/s      |
|                    |------------+-----------+-----------------------|
| Interface          |            5MB/s async., 10MB/s sync.          |
|--------------------+------------------------------------------------|
|Seek Time           |                                                |
| Random Seek        |                  28ms typical                  |
| Full Stroke        |                  60ms typical                  |
|--------------------+------------------------------------------------|
|Average Latency Time|                                                |
| 3600rpm (MCC3064SS)|                     8.3ms                      |
| 4300rpm (MCB3064SS)|                     7.0ms                      |
|--------------------+------------------------------------------------|
|Rotational Speed    |  3600rpm or 4300rpm depending on drive model   |
|--------------------+------------------------------------------------|
|Load/unload Time    |                 7 sec./5 sec.                  |
|--------------------+------------------------------------------------|
|Buffer Size         |                      2MB                       |
+--------------------+------------------------------------------------+

Overall write speed will be about 1/3 of the maximum transfer rate for standard disks with verification enabled. It is about 1/2 of the maximum when using LIMDOW media with verification, or normal media without verification. Maximum write speed is achieved with LIMDOW media and verification disabled.

The drive has 2MB of buffer RAM which improves read and write speeds. Operation of the read-ahead cache can be seen when reading data from the drive; the drive's own activity LED only flashes occasionally (corresponding to when data is actually read from the disk), whereas the Amiga's SCSI activity LED is on constantly (corresponding to data being transferred from drive to computer). Earlier MO drives had less buffer RAM; the first 640MB drives had 512KB. Some 5¼" drives have 8MB.

There is also a write-back cache which can speed up writes, especially small ones. You may wish to disable the write-back cache to guarantee data integrity. However, there should not be a problem if you are aware of how the cache works.

The read speed of my 640MB drive easily outpaces the capability of my 1991-vintage GVP SCSI controller. For writing, on my system I get over 1MB per second using a direct overwrite 640MB disk, FFS 43.20 and DiskSpeed 4.2.

For other types of drive, consult the manufacturer's web page.