/u 是 "不寫入 unformat 的資訊",
現在應該很少人在用了, 連 /? 都不列出來了, 不過好像還是可以下這個參數
您說的 "安全格式化" 應該是 /c
/c 是連目前標示為壞軌的 cluster 一起檢查
因為 format 預設是不檢查 "已標示為壞軌" 的部分

C:\_DOS>format.com /?
Formats a disk for use with MS-DOS.

FORMAT drive: [/V[:label]] [/Q] [/F:size] [/B | /S] [/C]
FORMAT drive: [/V[:label]] [/Q] [/T:tracks /N:sectors] [/B | /S] [/C]
FORMAT drive: [/V[:label]] [/Q] [/1] [/4] [/B | /S] [/C]
FORMAT drive: [/Q] [/1] [/4] [/8] [/B | /S] [/C]

/V[:label] Specifies the volume label.
/Q Performs a quick format.
/F:size Specifies the size of the floppy disk to format (such
as 160, 180, 320, 360, 720, 1.2, 1.44, 2.88).
/B Allocates space on the formatted disk for system files.
/S Copies system files to the formatted disk.
/T:tracks Specifies the number of tracks per disk side.
/N:sectors Specifies the number of sectors per track.
/1 Formats a single side of a floppy disk.
/4 Formats a 5.25-inch 360K floppy disk in a high-density drive.
/8 Formats eight sectors per track.
/C Tests clusters that are currently marked "bad."