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Format of DOS 4.0+ data segment subsegment control blocks

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Offset Size Description

00h

BYTE

subsegment type (blocks typically appear in this order)
"D"

device driver

"E"

device driver appendage

"I"

IFS (Installable File System) driver
(MS-DOS 7) high-loaded drive data table array (see #02603)

"F" FILES= control block storage area (for FILES>5)
"X" FCBS= control block storage area, if present
"C"

BUFFERS EMS workspace area (if BUFFERS /X option used)

"B" BUFFERS= storage area
"L" LASTDRIVE= current directory structure array storage area
"S" STACKS= code and data area, if present (see #01634,#01635)
"T" INSTALL= transient code

01h

WORD

paragraph of subsegment start (usually the next paragraph)

03h

WORD

size of subsegment in paragraphs

05h

3 BYTEs

unused

08h

8 BYTEs

for types "D" and "I", base name of file from which the driver was loaded (unused for other types)