Mouse Systems marketed its M-3 mouse as PC MOUSE. It improved on the earlier models by plugging straight into the serial port of the computer, requiring no external power supply. The one in the photos has a DB-25 serial plug.
Label on front: PC MOUSE
Label on the bottom includes the MOUSE SYSTEMS brand in block italic font with two triangular styled mouses in outline and black.
Made in the U.S.A. by Mouse Systems Corp SANTA CLARA, CA 95051 SVDC, 150mA MODEL M3 U.S. Patent 4364035
Stamped label between printed text:
MSC 901052-001/H SN SML BX52493 ASSY IN USA
Printed label below stamped ID:
FCC ID: CWE7VTB
On the body of this mouse between the optical holes is stamped faintly TEST #4.
This M-3 mouse uses a DB-25 hole serial plug that tapers to a blunted point, rather house shaped, for the fixed cord to the mouse. The plug could be screwed into the computer, but the screws are missing here. This serial mouse connected to the serial port. The bus mouse version connected to its own expansion card in the computer. There is no longer a separate power supply (as for the M-1 and M-2 models), so the computer provided the power.
The two oblong holes for the optical lights are parallel, not slanted as on the M-1 model. Behind the holes two little transparent balls convey the location to the optical readers inside. The original pearl white has aged to computer greige with tan/grey buttons.
The M-3 mouse came as the serial or the bus version. The PC Mouse Bus Plus was priced at $199, PC Paint for $99; PC Mouse (Serial) for $195; or bundled mouse and software for $220.
Imsi marketed their Mouse Systems OEM Model M-3 as an Optimouse PC Computer Mouse.
When programmers opine on old message boards for the Lillith mouse, or the Lisp, Magnolia, Metaphore or Perq mouse, etc., they are usually remembering the Mouse Systems M series mouse or else the Logitech mouses. Both maintained a sleek rectangular body with three buttons through several models. Both were used on workstations more often than personal computers (PCs) in the early days.