dennyt@prism.CS.ORST.EDU (Tom Denny) (01/25/91)
In the back of my Deskwriter book (Appendix 1) it states that the Buffer Size for a Deskwriter connected VIA serial is 16K; however, one connected using localtalk has only an 8K buffer. Next it goes on to say this about the I/O Interface: RS-422-A (serial) 57.6Kbps LocalTalk 230.4Kbps Here is my question: given a 32K file, which would give the quickest output: A Deskwriter connected to a lone mac using the serial interface or B Deskwriter connected to a lone (just one) mac using PhoneNet. I haven't been able to test this because I have not purchased the PhoneNet connectors yet. I would appreciate it if someone could send me any info they may have one this. Thanks Much! O_o Tom Denny dennyt@prism.cs.orst.edu (Preferred) #( )# tdenny@jove.cs.pdx.edu (CSNet) U - ack, thptt dennyt@pro-applephelia.cts.com
neff@hp-vcd.HP.COM (Dave Neff) (01/29/91)
>Here is my question: given a 32K file, which would give the quickest >output: >A Deskwriter connected to a lone mac using the serial interface or >B Deskwriter connected to a lone (just one) mac using PhoneNet. The DeskWriter typically has virtually identical performance both on LocalTalk (assuming the LAN is not real busy) and on 57K baud serial. The different input buffer size between LocalTalk and serial is not generally a performance concern, neither is the different effective IO transfer rates due to the fact that the speed of the DeskWriter is not IO limitted, rather it is either limitted by the speed of the Mac (on a Plus, SE, or Classic), or the actual speed the printer can fire dots. The DeskWriter makes heavy use of data compression techniques to eliminate the IO from being the bottleneck in either IO mode. There is one significant exception: Data that does not compress well (full page scanned images are a notable case) can be IO limitted, and in that case LocalTalk can be significantly faster than serial. If you do print these kinds of images, the speed improvement might be worth the cost of the PhoneNet conectors. One final note to confuse things further: Activating AppleTalk on the Mac will eat up some system RAM, that can then slow down the DeskWriter driver if you have only a 1 meg system. If you have 2 or more meg this is not a consideration. One RAM related speed up trick for systems with 2 or more meg is to be sure 64K or more of RAM cache is enabled in the control pannel. This can speed up the DeskWriter driver (along with other things). So in conclusion, if you have at least 2 megs of RAM, a fast Mac (16 megahertz CPU or more), enable some RAM cache, and compare 57K baud serial with 230K baud LocalTalk (and an idle LAN), performance will generally be virtually identical but in some cases LocalTalk can be faster. The 8K vs. 16K buffer in the two modes is not really a performance consideration at all. Basically, input buffer size is mainly an issue of how fast you get your Mac "back" if not using a spooler. With a character based printer, 16K can be several pages of a document. But on a graphics based printer (like the DeskWriter), the difference between 8K and 16K of input buffer is just a couple of seconds of print time, so in serial mode your Mac might be ready to use again a second or two before in LocalTalk mode, but the actual time for the printer to finish printing will not be affected by input buffer size. I hope this helps. I designed the DeskWriter LocalTalk and serial IO processor firmware, wrote a large amount of the firmware, and characterized the performance in both LocalTalk and serial modes, so I think you can believe my answer :-). Dave Neff neff@hpvcfs1.HP.COM
tgl@g.gp.cs.cmu.edu (Tom Lane) (01/30/91)
In article <1170010@hp-vcd.HP.COM>, neff@hp-vcd.HP.COM (Dave Neff) writes: > [a straight-from-the-horse's-mouth summary of a DeskWriter's performance > on serial vs. LocalTalk interfaces; in particular:] > ... Data that does not compress well > (full page scanned images are a notable case) can be IO limitted, and > in that case LocalTalk can be significantly faster than serial. > If you do print these kinds of images, the speed improvement might > be worth the cost of the PhoneNet conectors. Dave's authoritative summary omits one important fact: you don't need to shell out for those ridiculously expensive LocalTalk connectors if you are just going to connect one Mac to one printer. A plain "null modem" RS232 cable will do just fine. (Your Apple dealer will sell you one if you ask for an ImageWriter II cable; they're about $10.) NOTE: for safety with the cheaper cable, you should be sure the Mac and printer are both plugged into the same power outlet. The main reason AppleTalk is so expensive is that there are isolation transformers in the connectors. You don't need these if you have only one Mac and one printer and they are on the same power circuit. So, assuming you have enough system memory to handle the AppleTalk driver, by all means switch to AppleTalk. (I concur with Dave's warning that a 1MB machine may lose speed with AppleTalk; I don't think the CPU speed is an issue, however.) I have not tried this with a DeskWriter, but it works just fine with an HP LaserJet w/ PostScript. -- tom lane Internet: tgl@cs.cmu.edu UUCP: <your favorite internet/arpanet gateway>!cs.cmu.edu!tgl BITNET: tgl%cs.cmu.edu@cmuccvma CompuServe: >internet:tgl@cs.cmu.edu
neff@hp-vcd.HP.COM (Dave Neff) (01/31/91)
> Dave's authoritative summary omits one important fact: you don't need to > shell out for those ridiculously expensive LocalTalk connectors if you are > just going to connect one Mac to one printer. A plain "null modem" RS232 > cable will do just fine. (Your Apple dealer will sell you one if you ask > for an ImageWriter II cable; they're about $10.) True with ImageWriters and LaserWriters but not true with DeskWriters. DeskWriter only goes into LocalTalk mode when the isolation transformer is installed. This "auto lan detect" feature was added as an intended ease of use issue and we knowingly eliminated the ability to use "direct connect LocalTalk" with the DeskWriter. The fact that serial and LocalTalk gives comparable performance was one reason we saw no real need to support direct connect LocalTalk. That is, if you have a serial cable, just use serial mode, if you have LocalTalk connectors, then and only then you can use LocalTalk mode. In fact, the DeskWriter will automatically sense the cable and go into the proper mode. O.K., and I confess, the hardware to do the automatic lan detect was cheaper than adding a DIP switch :-). We also didn't have any cutout to mount a DIP switch and didn't have any general front pannel to allow manual selecting of the IO. Hence the automatic lan detect seemed like a good feature -- despite the inability to do direct connect LocalTalk. As for CPU speed being an issue, the CPU speed is not an issue with the IO, it is an issue with the DeskWriter driver. On slow Macs the driver cannot keep up with either IO. That was my point. If you have a slow Mac (Classic, Plus, SE), the speed of the DeskWriter will generally be limitted by the driver, not the IO or printer mechanism. Dave Neff neff@hpvcfs1.HP.COM