There's no limit to the number of serial ports. The maximum number for the traditional ports is 2 (COM1/COM3 and COM2/COM4). Plus you can attach additional serial port adapters to a USB port, up to 127 per controller.
Texas has the maximum number of ports in the United States, with over 1,000 miles of coastline and numerous ports, including the Port of Houston, which is one of the busiest in the nation.
IRQ 3 is for COM2 and COM4 (serial ports). See related link.
Most modern laptops lack any sort of "legacy" ports such as serial ports, let alone them having two. Some older laptops did have multiple serial ports, but there's little point in recommending one because there's no guarantee you could find one. There are options for adding serial ports to a laptop, such as a USB to serial adapter, or a PC card with additional serial ports.
serial ports are not in use any more, the new standard is usb
Many modern laptops don't have a serial port at all. The most common serial ports on desktop computers were the old style of mouse ports that look like this picture: http://i32.tinypic.com/29vtir.jpg
Standard serial ports have either 5 pins or 25 pins. Although are also serial ports, USB and PS/2 ports do not obey this rule.
The serial ports are named ttyS0, ttyS1, etc.And usually correspond respectively to COM1, COM2, etc. in DOS/Windows
These interface products turn regular USB ports into ports for serial products that can be connected to other serial components for communication uses.
No. Just the opposite.
yes
parallel and serial port
Ports 135 and ports 137 tell an attacker that the user has a Windows OS system. These ports are used by hackers.