dimare@ucla-cs.UUCP (09/17/84)
A salesman on a RS Comp Center told me that from his experience he could tell that the portable was slower than the model 4. He didn't say how much, but it was enough to convince him. I think he did mainly word processing. From the catalog you can't tell, as both are listed as 4MHz z80 machines, but I wonder if he was telling the truth. By the way, he told me this before knowing the new $1299 price (I think the 4P was more expensive, but I don't remember). Adolfo /// dimare@ucla-locus.arpa
uhclem@trsvax.UUCP (09/27/84)
#R:ucla-cs:-123000:trsvax:70700022:37777777600:1838 trsvax!uhclem Sep 27 11:28:00 1984 <Tomb of the Unknown .Core File> The Model 4P and the Model 4 both run at 4mhz. The secret is in a "wonderful" invention of hardware: RAM wait states. This allowed the use of memory that was too slow with a processor that was too fast. The Model 4P has never had any RAM wait states, so if the Z80 book says an instruction will take so long, that is how long it will take. The Model 4 has gone through three phases of existance. The first version had 2 wait states on each fetch. The middle version had 1, and the version they have been making recently has none. So if you compare a Model 4P to an older Model 4, the 4P will win every test. Since wait states on fetch operations penalizes short opcodes, and most OS's are written with tight code, I have seen a 20% speed difference between an old Model 4 and new one or a 4P. In fact, the Model 4P and the new Model 4s run faster than a Model II and its descendants, which had two wait states. The Model II/12 makes up for the wait states by not having wait states built into the video circuitry, having IM 2 interrupts, and DMA. The Model 4/4P has video waits, no DMA and no IM 2. The idea behind the video waits was to eliminate the screen "hashing" that happens when the CPU references video RAM when the character generator is trying to get a look. The Model I/II did not have them, the Model III had them as an option, and the Model 4/4P has them on all of the time. When the Model 4/4P are running at 2mhz, they all run a 2mhz, no wait states. <This information is provided by an individual and is not nor should be construed as being provided by Radio Shack or Tandy Corp. Radio Shack/Tandy Corp has no obligation to support the information provided in any way. So there.> "Thank you, Uh Clem." Frank Durda IV @ <trsvax!uhclem>