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PORT SPEED & MAXIMUM SPEED

Select the best Com Port speed and modem Maximum speed

The Serial COM Port is a physical link between the modem and the PC.
The default is far too low and slows downloading.
Select a much higher setting.

The Maximum speed is the modem-to-computer speed, and has an increased data load.
Select the highest available Maximum speed setting - provided you do not have a serious phone line noise problem.

PORT

The SERIAL COM PORT

The Port is a link between modem and computer. There are normally two Serial COM Ports which allow external devices to be connected to the computer. Internal modems have their own integrated 'Port'. Each Port has a speed that can be set independently. The Windows 95/98 default speed for all Serial Ports is just 9,600 bit per second - unacceptably low for a modern modem.

Arriving data is temporarily stored in the Port's FIFO buffer until collected by the CPU and delivered into main memory.

Overruns: If the Port speed is set too high then a busy CPU may not be able to empty the Port's FIFO data buffer before new data arrives there, and you may get a dangerous pile-up (Overruns) of data which gets damaged - that data will have to be resent. Also if set very high there may be no gain because there may not be sufficient new data in the arriving stream of data. Modern CPUs cope quite well with high Port speeds but some hardware items, video in particular, steal extra CPU time and cause Overruns to occur. Check by enabling the modem log.

If it is set too low then obviously the whole data transfer process will slow down - you will jog cautiously when you could sprint safely.

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PORT SPEED

Suggested Serial COM Port settings:

	 9,600 modem: select  9,600 bits per second
	14,400 modem: select 19,200 bps
	19,200 modem: select 38,400 bps
	28,800 modem: select 57,600 bps
	33,600 modem: select 57,600 bps or try 115,200 bps
	 faster modem: select 115,200 bps or 230,400 bps

If you do not have a 16550 serial port then try 38,400. You can check which Port type you have by running msd.exe from DOS.

Most often it is best to Disable the Only connect at this speed - when the 'line connection' is poor the modem will connect at a lower speed and will, hopefully, protect against some disconnections.

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TUNE THE PORT SETTING [1]    All Users

Change the Port setting in Device Manager

1. Select Start • Settings • Control Panel
2. Open System • Device Manager • Ports
3. Double-click the COM Port your modem is connected to
4. Select Port Settings
5. Select the new Port speed ("Bits per second")
6. (read 'Other Important Settings - next)
7. Click OK

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TUNE THE PORT SETTING [2]        All Users


While in Port Settings (in Device Manager) make sure you have these:
Data bits 8
Parity None
Stop bits 1
Flow control Hardware

Click on Advanced
Enable Use FIFO buffers (presuming you have FIFO)
Put the Receive and Transmit Buffer to maximum (right). These control your FIFO buffer - if you have any problems, try reducing the Receive Buffer.
Click OKs to exit

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TUNE THE PORT SETTING [3]        Intermediate Users

PORT BUFFER - ONLY if you use your modem in MS-DOS mode

You can ignore this setting if you use your modem only under Windows (and that's virtually all of us).

Under MS_DOS mode (Real, or True, DOS) the port buffer size is too small (but remember its size under a DOS prompt is the same as for Windows).

The size of buffer allocated in DOS mode can be adjusted in System.ini

Open System.ini.
In the [386Enh] section
Add the new lines (first line has nothing after the = )
COMxProtocol=
COMxBuffer=nnnn
where x represents the COMM Port number used by your modem
and nnnn is the new buffer size (usually 2048, perhaps 4096) e.g.
[386Enh]
COM2Protocol=
COM2Buffer=2048

If your link is normally slow, then you probably do not need to make the alteration.

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INTERNAL MODEMS        Advanced Users

Internal Modems

You may be able to increase the port speed beyond 115,200 bps. Many 33.6 and 56 Kbps internal modems have an in-built UART buffer that can exceed this limit.
Forcing such high speeds is not generally recommended. At best the gain will be marginal, and it may be the cause of Overruns where none previously existed. It may, however, be worthwhile for owners of a 56K modem (with a clear phone line).

You edit Win.ini.
• Select Start • Run; Type in notepad\windows\win.ini, and click OK.
• Scroll down to the [Ports] section, and edit in or add:
• Example: If the modem is installed on COM3, edit in this line:
      COM3:=230400,n,8,1,p
Where:    " 230400 " is the port speed in bps
   " n,8,1 " is a standard parity setting (you could try " E,7,1 ")
   " p " turns the hardware flow control ON - change to 'x' for OFF
• Now Save, and Exit Notepad. (Options may include 230400, 460800 or 921600 bps)
! First backup win.ini from _:\Windows. Also watch out for Buffer Overruns.

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OTHER TIPS        All Users

Highest Speed: You can try for the highest speed that does not cause Buffer Overruns. As a precaution you should use System Monitor to check for any problems, and drop your FIFO Receive buffer (in Modems • Properties • Connection • Port Settings) and/or the Port speed if they occur. You may also have to reduce it if your ISP, your phone line, or your telephone exchange is misbehaving. Read further explanations in Modems Menu.

External Modems & COM2
You should try to use COM2 if you have an external modem.
COM Ports are a low priority call for the CPU which has many 'more important' duties. However the CPU gives slightly higher priority to COM2 than to COM1.

Internal Modems
Remember that in addition to being installed in Device Manager, internal modems should also be installed and configured in the Modems option in Control Panel.

Overruns and Video Cards Advanced Users
Sometimes a Matrox Millennium or other Video Card may keep the CPU too busy to service the FIFO buffer adequately with resulting data Overruns (never experienced with this Site's MGA card). Altering its call priority in system.ini will allocate more CPU time to the Port's FIFO buffer. A slight deterioration in Video performance can be expected!.Try ONLY if you have Overruns.
For a MGA card: Open system.ini in Notepad and below the [386Enh] section add:
[mga.drv]
PCIChipSet=1

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OTHER TIPS (2)        All Users

If you need to investigate the ports on your computer, download:

AutoNOC Port Scan 1.0 - it checks the ports, freeware.

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MODEM MAXIMUM SPEED

Your modem 'talks' modem-to-ISPmodem - this is the connection speed, e.g. a V.90, 33.6Kbps or 28.8Kbps modem. It represents the best speed at which it can ever communicate with your ISP's modem along the phone line.

Your modem also 'talks' modem-to-computer - this is the Maximum speed, and appears in two places in Windows 95/98 - in DUN, and in Control Panel. It is advisable to change both, and use the same value in both.

Compressed data is (usually) decompressed at the receiving modem, and the now larger amount of data is sent thru to the computer. Therefore the Maximum Speed needs to be substantially faster that the connection speed just to keep up.

The limitations placed on Maximum speed are the speed supported by the COM Port, and the CPU speed of the computer. Windows 95/98 selects a very conservative default speed so that slower computers do not lose data during transfers. Increase it.

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TUNE MAXIMUM SPEED in DUN [1]         All Users

Change the Maximum Speed in DUN

• Select My Computer • Dial-Up Networking

• Right-click your Network Server icon, and select Properties

• Using the General tab sheet, select the highest Maximum speed available

• Disable Only connect at this speed - to allow connection at a lower speed when required.

• Click the OKs until out.

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ALSO CHANGE IT IN MODEMS [2]         All Users

Also change the Maximum Speed in Modems

• Select Start • Settings • Control Panel • Modems
• Double-click the Modems icon
• Using the General Tab sheet, choose your modem from the list, and click the Properties button
• In the next General tab sheet scroll down and select the same Maximum speed you used in Dial-up Networking. Click OK
• Disable Only connect at this speed - to allow connection at a lower speed when required
• Click OK and then Close

Note: Even with Only connect at this speed disabled, you may, at times, have to reduce the Maximum speed in order to maintain a good connection - if so, then your downloading will suffer, and you should discuss this with your ISP (while you check your settings, your phone line, and are investigating other ISPs!).

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

Copyright © LarryM 1998-2015 thpc@mail.com