On Oct 22, 2011, at 5:51 PM, Gregg Eshelman wrote: > > The Classic and the Plus both have a 68000 CPU at the same Mhz and the same > size screen. They can even run the same System Software and can both have up > to 4 meg RAM. > > Beyond that they're quite different. The Classic has a full 32bit ROM. The > Classic has a 1.44M floppy drive it can boot from. The only way the Plus can > use 1.44M disks is with a 3rd party external drive like the AEHD, which it > can't boot from. The Classic has Mini DIN 8 serial ports instead of 9 pin "D" > type. The Classic has ADB ports instead of the phone cord connections on the > Plus for keyboard and mouse. Finally, the Classic has SCSI that can handle > 1:1 interleave* and a version of System 6 in ROM.
The Plus also has Mini DIN 8 serial ports. That change was made from the 512K / 512Ke to provide room for the DB-25 SCSI connector. The plus has a RJ phone connector for the keyboard and a DE-9 connector for the mouse. > > *With the hard drives contemporary with the Plus, the sector interleave had > to be 2:1 or even 3:1 for best performance. 1:1 would work but was slower due > to the drive having to make more revolutions because the Plus' SCSI couldn't > read or write that fast. Newer drives spinning at 4,200 RPM or faster, the > interleave doesn't matter because the drives are turning fast enough it > doesn't take long for the right sector to come back around to the heads if > the Plus misses a read or write. Using an interleave other than 1:1 could > even make performance worse with a fast drive on a Plus. Newer drives with built in cache only need a 1:1 interleave as they suck the whole track into cache. 4200 RPM drives aren't that much faster than a 3600 RPM drive in terms of waiting for the disk to spin around again but they their faster speed means they will need an even higher interleave ratio. More than likely the reason they don't need anything but 1:1 interleave is due to cache. > Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting "I'm a designated driver on the Information Super Highway" -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
