Complete Pinout and Connection Guide for PC's
Backplane, Harddisk, CDROM, Floppydisk Parallel Port,
Serial Port, Network, PS2 & Monitor Cables
Everything for DCC (Direct Cable Connection of Win95/98),
Normal and Null Modem Cables, etc.

1.  Preface
2. The PC Backplane connections
3. Motherboard connections (IDE-0 IDE-1 FDD AC97 USB-X1 USB-X2)
4. Harddisk, Floppydisk, CDROM, CDR/W, DVD Connections and cabling
5. IBM Basic concepts of Computer Cabling.
6. IBM Parallel port Pin Descriptions (Wire name) for each pin number.
7. IOMEGA ZIP DRIVE / Any Scanner for Parallel port Cable Pinouts.
8. IBM Parallel Port Laplink Cable Pinouts.(for DCC of WIN9x.)
9. DCC (Direct Cable Connection) Feature of Win9x/Me/2000 Setup (updated)
10. IBM Serial port Pin Descriptions (Wire name) for each pin number.
11. Serial Port Null-modem Cable (for DCC of WIN9x.)
12 IBM Null-Modem pinouts. (DB-25 to DB-25), (DB-9 to DB-9) and (DB-25 to DB-9).
13 IBM Normal Modem (Cable) pinouts. (DB-25 to DB-25) and (DB-25 to DB-9).
14 The pin-configuration of Internal Serial Cables inside Cabinet.
15 All about network Cable (RJ45 Jack Basics) (updated)
16 STANDARD SVGA/VGA Monitor Cabling
17 USB (Universal Serial Bus) Fundamentals
18 Keyboard Connector Pinouts (ATXT normal to PS2)
19 Multimedia connections (mic, line-in, lineout/speaker)



Here are several diagrams and tables explaining parallel port, serial port and null-modem configurations, which are mostly available on Internet.

2. The PC Backplane Connections

Mouse (top-left) type PS2S

Keyboard (bottom-left) type mini-din-S

USB-A(#1) USB-A(#2) NIC(T45)

Parallel (DB-25S) Serial (DB-9P) SVGA Video (DB-15VS)

Game (DB-15S) Mic (Mini-Stereo) Line-out (Mini-Stereo) Line-in (Mini-Stereo)


3. Motherboard Connections

mbd connectionsMBD
Motherboard's vary in size complexity features etc. They do however contain some basic features and these all conform
to set standards. Of the basic features motherbaords contain, there will always be card slots (upper left) Backplane connections
(upper right) , CPU [Slot or socket] and Memory slots

Optional items found on the motherbaord consist of :

Before the days of Pentium, features like harddisk,floppy,parallel,serial,video,nic,modem,sound were done by
plugging cards into the card slots. Features like USB, AGP, Firewire, SATA were not available.

4. Harddisk Floppydisk CDROM CDR/W DVD connections

ide connectionside cables

The connector on an IDE cable
Pin Description Pin Description
1 Reset 23 -IOW
2 Ground 24 Ground
3 Data Bit 7 25 -IOR
4 Data Bit 8 26 Ground
5 Data Bit 6 27 I/O Channel Ready
6 Data Bit 9 28 SPSYNC: Cable Select
7 Data Bit 5 29 -DACK 3
8 Data Bit 10 30 Ground
9 Data Bit 4 31 RQ 14
10 Data Bit 11 32 -IOCS 16
11 Data Bit 3 33 Address Bit 1
12 Data Bit 12 34 -PDIAG
13 Data Bit 2 35 Address Bit 0
14 Data Bit 13 36 Address Bit 2
15 Data Bit 1 37 -CS1FX
16 Data Bit 14 38 -CS3FX
17 Data Bit 0 39 -DA/SP
18 Data Bit 15 40 Ground
19 Ground 41 +5 Volts (Logic) (Optional)
20 Cable Key (pin missing) 42 +5 Volts (Motor) (Optional)
21 DRQ 3 43 Ground (Optional)
22 Ground 44 -Type (Optional)

Note that the last four pins are only used by devices that require power through the ribbon cable. Typically, such devices are hard drives that are too small (for example, 2.5 inches) to need a separate power supply.

The motherboard may contain "scotch connectors" for IDE-0 IDE-1 and floppy. Each IDE connector can
operate 2 drives in a master and slave configuration. For the floppy connection there may be 1, 2 or 4 drive
connection points on the cable. Where the Harddisk connector is 40 pin header the floppy is a 34 pin header.
Pin one will have a colored band at the one edge of the ribbon cable. The motherbaord may employ missing pins
and keyway notches to help make sure the connections are put in the right way.

When plugging in the connectors onto the drives, please note that you must be weary of jobber cables which
may have been assembled incorrectly by reversing connector such that pin 40 or pin 34 aligns with the colored
band end or may not even use a color coded ribbon cable. Placing the cable the wrong way will damage the
drive, powersupply or motherboard in some cases. In the case of floppies, it can cause the drive lite to come on
and stay on. [for linux people IDE-0 pri = hda IDE-0 sec = hdb IDE-1 pri =hdc IDE-1 sec = hdd]

When using 2 harddisks on one cable, the primary drive must have a jumper on it set to master. The secondary
drive must be set to slave. Be sure to orient the pin 1 correctly. For CDROM CDR/W and DVD treat them
exactly as if they are harddisks again setting the jumper to master or slave accordingly.

Floppy drives come as three varieties and in many recording densities. Typically you will only find the
3.5"-1.44MB or 3.5"-2.88MB versions now-a-days. There are however still 8"-1MB 8"-5MB 5.25"-90KB
5.25"-160KB 5.25"-320KB 5.25"-360KB 5.25"-1.2MB and 3.5"-720KB kicking around at swap meets. Also
note that Zip-drives exist that use floppy cabling and have storage of 120MB. Floppy cables with one connection
will have either a "Scotch" or a cardedge connection on it. Cardedge connections are for use with 8" and 5.25"
drives. Scotch are for 3.5" and zip drives. Cables with 2 connectors for drives will either have 1 scotch and 1
Cardedge (both configured as drive a:) or 2 Cardedge with wiring twisted between the connectors or 2 Scotch with
wiring twisted between the conenctors. Where cables have twisted wirng, the connection nearest the motherboard
end is for drive a: and the other is for drive b:. Many floppies need the jumpers on the drives set to A: B: or cable
Select in order to be recognized [For linux people a: = fd0 and b: = fd1]

Audio : CDROM, CDR/W, and DVD contain an extra connector used to supply audio information to a sound
card one end is usually a a mini 3 pin header with keyway while the drive end may be either a 4 pin connector flat
header or a 3 pin mini header. If yours uses the 4 pin flat header you will note a missing pin on the header to help
you connect it


Connections when dealing with computers use the ideals of Plug vs Socket
Pin vs Hole and Male vs Female.

In essence the Plug/Pin/Male fits into the Socket/Hole/Female.

The connections are one of :

Female MT connections on the computer are:

Male MT connections on the computer are:


Looking at the DB - 9 and 25 pin connections widely used for parallel and serial

Each pin has a number assigned to it. When connecting null modem, for example, it is important to know these numbers in order to select the correct cables, or when making your own cables.

DB-25 Connector

Chart #1 (Female) DB-25S
db 25 socket

Chart #2 (Male) DB-25P
db 25 male

DB-9 Connector
Chart #3 (Female) DB-9S
db 9 socket
Chart #4 (Male) DB-9P
db 9 male
Type of connection Computer End MT- Cbl Device end
Computer Parallel port Printer DB-25S DB-25P Centronics (see below) Centronics
Parallel Scanner DB-25S DB-25P DB-25P DB-25S
Scanner to Printer DB-25S (scanner out) DB-25P Centronics Centronics
Computer Parallel to abcd switch DB-25S DB-25P DB-25P DB-25S common
abcd switch to Printer(s) DB-25S (output a->d) DB-25P Centronics Centronics
Computer to Serial Port Printer DB-25P or DB-9P DB-25S or DB-9S DB-25S or DB-9S DB-25P or DB-9P
Computer to modem DB-25P or DB-9P DB-25S or DB-9S DB-25S or DB-9S DB-25P or DB-9P



6. IBM Parallel port Pin Descriptions (Wire name) for each pin number.

Following is the chart for transmission of Data via Parallel Port.

Pin Assignments of Parallel Port (LPT1)
Female DB-25 on PC
<= in
=> out
Name of
Function Notes
=> out 1 1 -Strobe C0- Set Low p1ulse >0.5 us to send
=> out 2 2 Data 0 D0 Set to least significant data
=> out 3 3 Data 1 D1 ...
=> out 4 4 Data 2 D2 ...
=> out 5 5 Data 3 D3 ...
=> out 6 6 Data 4 D4 ...
=> out 7 7 Data 5 D5 ...
=> out 8 8 Data 6 D6 ...
=> out 9 9 Data 7 D7 Set to most significant data
<= in 10 10 -Ack S6+ IRQ; Low Pulse ~ 5 uS, after accept
<= in 11 11 +Busy S7- High for Busy/Offline/Error
<= in 12 12 +PaperEnd S5+ High for out of paper
<= in 13 13 +SelectIn S4+ High for printer selected
=> out 14 14 -AutoFd C1- Set Low to autofeed one line
<= in 15 32 -Error S3+ Low for Error/Offline/PaperEnd
=> out 16 31 -Init C2+ Set Low pulse > 50uS to init
=> out 17 36 -Select C3- Set Low to select printer
== 18-25 19-30,
Ground - Do not connect any of these grounds to a shield

Imp. Note:
Some cables, ports, or connectors may not connect all grounds. Centronics pins 19-30 and 33 are "twisted pair return" grounds, while 17 is "chassis ground" and 16 is "logic ground".

"<= In" and "=> Out" are defined from the viewpoint of the PC, not the printer. The IRQ line (-Ack/S6+) is positive edge triggered, but only enabled if C4 is 1.

7. IOMEGA ZIP DRIVE / Any scanner for Parallel Port Cable Pinouts
(Also called Straight-through PP Cable)

Most of the External Parallel Port devices like IOMEGA ZIPDRIVE and most Scanners use Straight-through Parallel Port cable with Straight pinouts like 1 to 1, 2 to 2, 3 to 3 and so on up to 25 to 25.  The straight-thru cable is also used for Printer Data Switches between motherboard and the data-switch. 

8. Parallel Port Laplink Cable Pinouts

Laplink cable is used to link two PCs with MSDOS 6.0 or later, very effectively by using INTERSVR.EXE (on Host) and INTERLNK.EXE (on GUEST) PCs.  But it can also be used to data-transfer at faster speed with DCC Feature of Win9x/Me/2000.

If you are seeking to buy a Parallel port Laplink cable, or trying to make your own cable, you should know what pins need to be switched in order to make it. Below is a chart of what pins go to what on the other end. Only 18 pins are used in a Laplink Cable, therefore I will only show those eighteen here.

To make this cable we need
1. TWO numbers of DB-25 Male Sockets.
2. Shielded Cable with 18 cores (lines of wires).

DCC Parallel Laplink Cable Pinouts.
Male DB-25 ==>> Male DB-25
1 Both Not used
2 to 15
3 to 13
4 to 12
5 to 10
6 to 11
7 Both Not used
8 Both Not used
9 Both Not used
10 to 5
11 to 6
12 to 4
13 to 3
14 Both Not used
15 to 2
16 Both Not used
17 to 19
18 to 18
19 to 17
20 Both Not used
21 to 21
22 to 22
23 to 23
24 Both Not used
25 to 25
Pinbody* to Pinbody

* = In my cable one wire was attached to the metal body of the Male pins on both sides. Total 18 wired cable is necessary for this cable including one wire for Body of the pin too.

SPEED: Parallel port Laplink cable is little faster than Serial port Cable because of more numbers of cores of wires used in Parallel port cable (25 pin) than Serial port Cable (9 pins). The expected speed is 2000kbytes/second but it is extremely dependent on the different quality chipset structure of Parallel Ports on different makes of the Motherboards. Some even reported me the lowest speed of 60kb/sec even though all other settings are correct. Its recommended that you setup LPT1 mode as only "ECP/EPP" or "ECP" mode in bios to get better speed, and not the "Normal" (4bit/8bit) modes.  The latest tests done by me on modern motherboard proved that serial port transfers are equal or little slower than parallel ports.

ONE Word of caution: Please note that if you set your printer port to ECP/EPP older model
printers will not function correctly if at all using win98se/win2k/winnt/winme or wincp. Microsoft
in their infinate wisdom decided to rewrite the printer driver dll to run at fastest speed if the port
is set as such. If you still need these older economy style dot matrix ribbon method printers you must
add an additional printer port card to the pc so you can have one set normal and one set ECP/EPP.

9. Important Points  for DCC (File-transfer) of Win9x/ME/2000 with LAPLINK (Printer port) Cable or Null-Modem (serial port) Cable.

Laplink cable is also successfully used to link two PCs for only FILE TRANSFER (not playing Games), with WIN95 and Direct Cable Connection program with common protocol as "NETBEUI" on both Computer's Network Section of Control Panel. In Network section you must have installed "Client for Microsoft Networks", "File and Printer Sharing for Microsoft Networks" and two useful and important protocols, which are "TCP/IP" and "NetBEUI".  Both the options in "File and Print Sharing" button should be selected (checked) to allow all users to access files and printer. You should see at least these items in NETWORK section in Control Panel.
  1. Client for Microsoft Networks
  2. TCP/IP
  3. Netbeui
  4. File and Printer Sharing for Microsoft Networks

There are some more items found already in above list such as "Dial-up Adaptor" or "Microsoft Family Logon" , but leave them as it is as they are not going to make any difference.  The windows reboots/restarts after all changes/additions are made.

You should also share the Disks on both computer by right-clicking on disks found inside "My Computer" folder on desktop.  This will show the disks available for file transfer on both computers.

Now connect the Cable. Then start DCC program on one computer in HOST mode and on other machine in GUEST mode. Also only two computers can be connected to each other for only FILE TRANSFER and not for anything else. The rest is explained in HELP and Troubleshooting Section of WIN95 itself.

10. IBM Serial port Pin Descriptions (Wire name) for each pin number.

For following all connections we may use these chart for transmission of Data via Serial Port.

Pin assignments
2 TD Transmit Data
3 RD Receive Data
4 RTS Request to send
5 CTS Clear to send
6 DSR Data Set Ready
7 SG Signal Ground
8 DCD Data Carrier Detect
20 DTR Data Terminal Ready
22 Ring Ring Indicator
Pin Assignments
1 DCD Data Carrier Detect
2 RD Receive Data
3 TD Transmit Data
4 DTR Data Terminal Ready
5 SG Signal Ground
6 DSR Data Set Ready
7 RTS Request to Send
8 CTS Clear to Send
9 Ring Ring Indicator

IMP. NOTE : In DB-25 serial cable following numbered pins are NOT USED. They are 1, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 24 and 25. IMP. NOTE : In DB-25 serial cable following numbered pins are NOT USED. They are 1, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 23, 24 and 25.

11. NULL-MODEM cable for DCC file transfer?

Yes! About a DCC of Win9x thru Serial Port a very important information I am going to put over. Please read carefully. We can also use Null-modem cable to use with DCC for Data transfer on Serial port with all above settings identical as we use for DCC with Laplink Cable on Printer Port. Please do not get confused with DTE and DCE descriptions on that site as DTE is DB9 or DB25 MALE pin as found on system and DCE is DB9 or DB25 Female socket/pin as found on Modems. We usually get MALE DB9 or DB25 pin serial ports on our computers which can also be called DTE type port.

Speed: The speed I tested with the help of several utility softwares proved that the transfer can go really very high upto 2000 kbytes per second on modern pentium motherboards.  Only thing which should be done is that we must set the serial port speed to 115200 bits in Device Manager section of System settings in Control Panel of Win9x. This is more than the speed of parallel port transfer of files with laplink cable.  Of course all motherboards do not support this.

So, just Enjoy. Next section is how to build your own Null-Modem cable.

12. IBM Null-Modem Cable pinouts.
(DB-25 to DB-25), (DB-9 to DB-9) and (DB-25 to DB-9).

For making Null modem cable following is a chart of pinouts. Only 8 pins are used in a null modem, though there are 25 pins on DB-25 socket. You need 8 or 9-wired cable with two DB-25-Female pin socket or DB-9-Female pin socket or one of both.

IMPORTANT : Both pin sockets must be of FEMALE type. This may not be applicable on some machines, so please check your serial ports of both the machines as there must be MALE pins at back of your both computers.

Chart #6 Chart #7 Chart #8
Null-Modem Pinouts
DB-25 to DB-25
2 to 3
3 to 2
4 to 5
5 to 4
6 and 8 to 20
7 to 7
20 to 6 and 8
Null-Modem Pinouts
DB-9 to DB-9
1 and 6 to 4
2 to 3
3 to 2
4 to 1 and 6
5 to 5
7 to 8
8 to 7
Null-Modem Pinouts
DB-25 to DB-9
2 to 2
3 to 3
4 to 8
5 to 7
6 and 8 to 4
7 to 5
20 to 6 and 1

Now why this cable is called null modem without using the modem?

by grimace :- That's good question. But if you think a little bit, you will get an answer that as we don't use modem and use modem-like connection on two computers staying together, so we call it Null-Modem Connection.

Most important is, as you may know that modem have its own data-transmission method and special combination of the data input-output is required to be configured to each pin of the modem cable so the special modem to computer cable is used. But if you give more attention on CHART#11 and CHART#12 of my page you will get an idea that how actual the DATA-TRANSMISSION takes place. Now if we want to play multiplayer game from remote areas we need to connect systems with MODEMS as follows...

A's Computer ###### A's MODEM ------> TELEPHONE CO.----->B's MODEM ###### B's Computer

In above (1st) diagram '######' is the cable which connects the Computer to MODEM. The one which comes with modem.

A's Computer =================== B's Computer

In this (2nd) diagram '===========' resembles the null modem cable emulating the 1st transmission. Now in above method the Null modem Cable's pinouts are adjusted in such a way that it emulates the modem connection to the same DATA-TRANSMISSION as MODEM to Computer connection requires. See chart#9 and #10. Therefore it is called Null-Modem cable. Hope I could explain you the whole saga. <phew>

13. IBM Normal-Modem Cable pinouts. (DB-25 to DB-25) and (DB-25 to DB-9).

IMPORTANT : Both pin sockets must be of DIFFERENT type. This means that for modem-side of cable we need to use MALE type of DB-25 pin. And on CPU side of cable we need to use FEMALE type of DB-25 or DB-9 pin.

Chart #9 Chart #10
Normal-Modem Pinouts
DB-25 to DB-25
2 to 2
3 to 3
4 to 4
5 to 5
6 to 6
7 to 7
8 to 8
20 to 20
22 to 22
PinBody* to Pinbody*
Normal-Modem Pinouts
DB-25 to DB-9
2 to 3
3 to 2
4 to 7
5 to 8
6 to 6
7 to 5
8 to 1
20 to 4
22 to 9
PinBody* to Pinbody*

* Pinbody is OPTIONAL. We easily get cable with 9-wires in it, but not 10 then Pinbody can be attached with shielded wire. The one which I examined from a reputed company was having body of pins connected with shielded wire (let's assume earthing line.)

14.The pin-configuration of Internal Serial Port Cables inside Cabinet.

The pin-configuration of internal serial cables (the one that connects from the motherboard to the case) are different for different motherboards, which come in two types. One with straight pins as in old mobos like 286/386/486. And another is twisted style cable like in latest Pentiums. The MALE DB9 pin is connected to serial port on motherboard with 9 wired cable in following two types. Both Serial ports on motherboard have 10 wires but only 9 of them to connect to MALE DB9 Serial Pins. Please do not connect 10th core anywhere.

Chart# 14
DB9 Pinouts of
on 286/386 systems
Cable Wire number
on motherboard
Wire Connected
to male DB9 pin
on cabinet.
1 Red Wire 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
Chart# 15
DB9 Pinouts of
on modern systems
Cable Wire number
on motherboard
Wire Connected
to male DB9 pin
on cabinet.
1 Red Wire 1
2 6
3 2
4 7
5 3
6 8
7 4
8 9
9 5

The MALE DB-25 pin is connected to serial port on motherboard with 9 wired cable (Yes, 9-wired cable) in following two types. Both Serial ports on motherboard have 10 wires to connect to MALE DB25 Serial Pins as follows. Take it.

Chart# 16
DB25 Pinouts of
on 286/386 systems
Cable Wire number
on motherboard
Wire Connected
to male DB25 pin
on cabinet.
1 Red Wire 8
2 3
3 2
4 20
5 7
6 6
7 4
8 5
9 22
Chart# 17
DB25 Pinouts of
on modern systems
Cable Wire number
on motherboard
Wire Connected
to male DB25 pin
on cabinet.
1 Red Wire 8
2 6
3 3
4 4
5 2
6 5
7 20
8 22
9 7

NOTE: The 10th Core Wire from motherboard is an Optional line which can be connected to pin 1 of DB25 with no harm.

IMP: Above are the exact pinouts of the all four types of working serial ports.


19 Multimedia connections for Mic line-in lineout/speaker

Shown below is the connections for the audio jacks and plugs that comprize your multimedia
system. The plugs and sockets are all standard mini type. Acceptable use of the speaker jack
is to an 8 ohm speaker or earphone. Some soundcards can be set to output to either speaker
out or lineout modes and in this case if you set to lineout mode do not connect speakers. The
line out mode is for sending a signal to the auxiliary input of an amplifier only. The Mic used in
computer multimedia is condensor type only! to use other types you must use the auxilary input
from an acceptable auxiliary output of an amplifier. You can over power both the outputs and inputs
of sound cards easily thus causing damage by using too high of load.

audio jackaudio server