I've been studying the DRV files a bit.
VGA320:
seg000:0000 seg000 segment byte public 'CODE'
seg000:0000 assume cs:seg000
seg000:0000 assume es:nothing, ss:nothing, ds:nothing
seg000:0000 jmp entry
seg000:0003 align 2
seg000:0004 dd 87654321h ; Driver marker
seg000:0008 db 0 ; D_VIDEO
seg000:0009 aDrvID db 6,'vga320'
seg000:0010 aDrvName db 43,'VGA or IBM PS2, Models 25 & 30 - 256 Colors' ; not quite right
seg000:003C dd 0FEDCBA98h ; ExtDrv marker
seg000:0040 word_40 dw 80h ; VGA
seg000:0042 align 4
seg000:0044 dispatch dw offset D_DETECT ; DATA XREF: seg000:0DA7 (that's in entry --K)
seg000:0046 dw offset D_INIT
seg000:0048 dw offset D_TERMINATE
...
VESA:
seg000:0000 seg000 segment byte public 'CODE'
seg000:0000 assume cs:seg000
seg000:0000 assume es:nothing, ss:nothing, ds:nothing
seg000:0000 dw 0 ; There's no jump here, child.
seg000:0002 dw 0
seg000:0004 dd 87654321h ; Driver marker
seg000:0008 db 0 ; D_VIDEO
seg000:0009 aDrvID db 4,'VESA'
seg000:000E aDrvName db 12,'VESA 640x400'
seg000:001B dd 0FEDCBA98h ; ExtDrv marker
seg000:001F dw 80h ; VGA
seg000:0021 dw 0
seg000:0021 seg000 ends ; Yup. --K
GENMIDI:
seg000:0000 seg000 segment byte public 'CODE'
seg000:0000 assume cs:seg000
seg000:0000 assume es:nothing, ss:nothing, ds:nothing
seg000:0000 jmp near ptr entry
seg000:0000 ; ---------------------------------------------------------------------------
seg000:0003 align 2
seg000:0004 dd 87654321h ; Driver marker
seg000:0008 db 1 ; Music
seg000:0009 aDrvID db 4,'dude' ; Most music drivers I've checked have this.
seg000:000E aDrvName db 37,'General MIDI for Roland MPU interface' ; wait no
seg000:0034 dd 0FEDCBA98h ; ExtDrv marker
seg000:0038 dw 200h ; MPU Midi
seg000:003A db 0
seg000:003B db 0
seg000:003C aV1_08 db 'v1.08'
... ; Dispatch table is much further down.