1. CS-401 Computer Architecture Assembly Language Programming
Lecture-35
DOS Services
Secondary Storage

2. Lets revise the last lecture

3. Secondary storage

4. int 0x13 Disk Services 8 3 1 1 5 2 2 2 2 2 4 File name Extension
File name
Creation
Date Time
Extension
File Size
Last Accessed Date
Starting Cluster High
Time
Date
Starting Cluster Low
Flag Byte
Reserved

5. int 0x13 Disk Services AH = 0*00 DL = Drive RETURN AH = Status
CF = Clear on success
CF =Set on error

6. int 0x13 Disk Services Read Sector to Memory AH = 0x02
AL = sector to read
CH = cylinder number (low 8 bits)
CL = sector number 1-63 (bits 0-5)
cylinder number (high 2 bits)
DH = head number
DL = drive number
ES:BX = data buffer
Return
CF = set on error
AH = status
AL = sectors transferred

7. int 0x13 Disk Services Write Disk Sector AH = 0x03
AL = sector to write
CH = cylinder number (low 8 bits)
CL = sector number 1-63 (bits 0-5)
cylinder number (high 2 bits)
DH = head number
DL = drive number
ES:BX = data buffer
Return
CF = set on error
AH = status
AL = sectors transferred

8. int 0x13 Disk Services Get Drive Parameters AH = 0x08
DL = drive number
Return
CF = set on error
AH = status
BL = drive type
CH = maximum cylinder number (low 8 bits)
CL = maximum cylinder number (high 2 bits)
maximum sector number (bits 0-5)
DH = maximum head number
DL = number of drives

9. int 0x13 Disk Services Extended Read AH = 42h DL = drive number
DS:SI = disk address packet (below)
Return
CF = set on error
AH = status
disk address packet

10. int 0x13 Disk Services Address Packet 1 1 2 4 8 Absolute Block
Absolute
Block
Number
Transfer Blocks
Blocks
Size
Reserved

11. int 0x13 Disk Services Extended Write AH = 43h AL = write flag
DL = drive number
DS:SI = disk address packet
Return
CF = set on error
AH = status

12. Partition Table
x4 2
MBR
Partition Entries
Signature

13. Partition Table Partition Entry 1 3 1 3 4 4 Status Starting CHS
Starting
LBA
partition
Size of
Starting CHS
Ending CHS
Status
Partition Type