Different types of PC Mice
Apr 08 '01 (Updated Jun 07 '01)
The Bottom Line Different types of mice. Ps/2 still the most prevalent and accurate, USB frees system resources for other toys and is hotswappable.
The mouse device has been around almost as long as the home computer. There have been several different types of technology and I'll attempt to describe each here.
The first affordable home computers came out in the late 80's early 90's, mice commonly came with these systems. The early systems did not have the commonly seen ps/2 connection that is so common in today's systems, nor did they have USB ports, those advances came much later. The first computer mice used one of the two serial ports (usually COM1 or COM2) that come on the majority of pc computer systems. If the two onboard serial ports were already in use by other devices an additional card could be added to the computer with two more serial ports on it. A serial mouse uses a serial connector that fits on, and screws down onto, one of the serial port connectors on the back of your computer.
Serial mice were fairly easy to install since your computer should have arrived with two functioning serial ports already turned on. Serial mice, since they used the serial port were very prone to problems caused by irq conflicts and software/hardware conflicts. The early versions of windows sometimes had a hard time seeing a serial mouse at startup unless you moved it while windows was starting up. The advent of modems in every system made the serial mouse even more of a pain because a modem often tried to use some of the same resources as the mouse since it was also a serial device.
A less common type of early mouse was known as a "bus mouse" this also was basically a serial mouse but it came with its own interface card that had to be properly installed in the machine before the mouse would work. Because serial and bus mice could end up with different addresses and irq allocations in different systems they were troublesome and this standard was abandoned for the still common ps/2 mouse seen in today's systems.
There were several incarnations of serial mouse, most had the familiar ball and roller mechanisms but a few put out by companies such as Honeywell had moving rubberized feet or light sensing schemes that needed a special lined mouse pad to operate.
The Trackball: Another later mousing development was the trackball. A trackball usually works in much the same way as a mouse, the big difference is that it doesn't require as much room because the base is stationary while the ball moves around inside the device. A trackball is really just an upside down mouse. Most trackballs use the same type of sensing mechanisms as a regular mouse to detect the ball's movements. Perhaps the forerunner of today's optical products could be seen in some microsoft products that used a special patterned ball to track the ball's movement optically within the trackball housing. Like regular mice, trackballs also were available in serial and ps/2 varieties. If you had limited space on your desk a trackball was more desireable but they offer less fine control than a regular mouse does.
The PS/2 Port: The invention of Ps/2 meant that mouse makers could design their products knowing exactly what hardware address and irq the product would use because the motherboard was already setup to assign those same resources to a ps/2 port on every board that had one. The ps/2 specification was the most prevalent type of mouse for several years and is still found on systems today.
USB (Universal Serial Bus) is the latest type of mouse to be developed. Windows 95b was the first common operating system to offer support for USB and it only offered very limited support for a few USB products. Windows 98 was the first operating system to offer extensive support for the huge variety of USB devices on the market today.
The main advantage to USB is that no matter how many devices are hooked up to it, the USB controller only uses a very limited number of resources (usually one IRQ and one hardware address) for all of them. The other big advantage to USB is that devices can be plugged into and removed from the USB bus with the machine running, i.e. it's "hot swappable."
Today we have so many choices for toys to put in our computers that we need to reclaim every possible hardware address and irq for use by other things. A modern machine may come with serial ports but most of us don't use them because so much is available as a USB device that they aren't needed. The simple act of shutting off the onboard serial ports frees two irq's for use by something else in the system. Using a USB mouse and keyboard also frees up irq12 which is always reserved for ps/2 devices unless none are in use.
USB mice are not quite as accurate as a Ps/2 or serial mouse but most of us never would notice the difference. USB/ps2 mice come in the common ball and roller mechanism style, a special optical type that works by tracking spots on a special mouseball and the newest all optical laser mice. Many currently sold products can work as both a ps/2 mouse or a usb mouse, a special adapter comes in the package so you can use it on either bus.
USB mice work very well but many motherboards have lacking support for them in dos. You usually must have a ps/2 keyboard and mouse installed before you load windows for the first time.
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