Thank you for all the answers so far:) Jarry explained the bandwidth a printer consume cannot be too high for USB 2.0 slots. This knowledge is very helpful, however at this moment the sparc box only have USB 1.x slot, driven by ohci, as I explained.
Richard Fish kindly explained the mechanism behind print processing, a printer make take a lot of time to process the data already sent. In my case I completely forgot to mension I was using inkjets, the inkjet takes rastered image data produced by GutenPrint. Thus I assume most image processing is done on the print server, which is usually at 30% load when printing, that means it should be able to handle another printer. Richard also suggested upgrading to a network printer, so far it is a very good solution too for my case. I think James provided most helpful information for my case, and thank you for so detailed and careful explanation. As he suggested I try to look for more hadwar data. It turns that my USB device is not USB 2.0 but I also noticed the two USB slots have diferent membase and IRQ. I wish to compare the sparc station with my desktop. On my x86 desktop there are 4 USB slots, dmesg shows that two UHCI device discovered, further on each device, a uhub of two slots are discovered. From my understanding, the situation of "Sharing bandwidth" James described should happen between two USB devices on the one same chip, on one uhub. For two devices, they perhaps don't share resource. In my case, my two USB 1.0 slots seems to be hot using a uhub, shall the two printer compete for resource on this situation too? Another small question I hope someone with professional knowledge can help. I was told ECP/bidirectional printer cable can handle 2Mbps data transfer, that seems to be suggesting using parallel cable is as good as using USB1 cable (as USB1 is supposed to handle 1.2Mbps ony), or even better. Is it true? Here is my lsusb when I just tried to plug another USB printer and make all slots occupied. # lsusb Bus 002 Device 001: ID 0000:0000 Bus 002 Device 002: ID 03f0:1617 Hewlett-Packard Bus 001 Device 001: ID 0000:0000 Bus 001 Device 002: ID 04b8:0005 Seiko Epson Corp. Stylus Printer Here is part of my dmesg host/usb-ohci.c: USB OHCI at membase 0x1ff00520000, IRQ 10,7d4 host/usb-ohci.c: usb-02:02.0, NEC Corporation USB usb.c: new USB bus registered, assigned bus number 1 hub.c: USB hub found hub.c: 3 ports detected host/usb-ohci.c: USB OHCI at membase 0x1ff00522000, IRQ 10,7d5 host/usb-ohci.c: usb-02:02.1, NEC Corporation USB (#2) usb.c: new USB bus registered, assigned bus number 2 hub.c: USB hub found hub.c: 2 ports detected hub.c: new USB device 02:02.0-1, assigned address 2 usb.c: USB device 2 (vend/prod 0x4b8/0x5) is not claimed by any active driver. usb.c: registered new driver hid hid-core.c: v1.8.1 Andreas Gal, Vojtech Pavlik <[EMAIL PROTECTED]> hid-core.c: USB HID support drivers usb.c: registered new driver usblp printer.c: usblp0: USB Bidirectional printer dev 2 if 0 alt 0 proto 2 vid 0x04B8 pid 0x0005 printer.c: v0.13: USB Printer Device Class driver -- gentoo-user@gentoo.org mailing list
