Re: How fast is a IIgs?

[jmk3@crux4.cit.cornell.edu (Jay Krell)]

CHEEZWHIZ@news.delphi.com (CHEEZWHIZ@DELPHI.COM) writes:

>As you noted, the clock speed is 3.6 MHz.  Unfortunately, the IIgs has to 
>deal with a bank of very frequently used memory which is only rated at 
>1MHz (the IIe emulation memopry, but the GS uses it in native mode, too), 
>so it's constantly dialing down to 1MHz to access that memory.  All in 
>all, it actually averages about 2.8MHz, which is what you'll hear most 

It's already been stated correctly, but, again, the actual clock speed
is 2.8 MHz. There's about a 10% speed hit for code running RAM instead of
ROM, and...I'm fuzzy here, but, like, all accesses to banks E0
and E1 are at 1 MHz, and shadowed writes, such as for text, video and? I/O?
to banks 0 and 1 ("IIe emulation memory") are at 1 MHz?
So, code in banks E0 and E1 runs at 1 MHz, right? Those darn vectors...
(and chunks of code)

Is the reason for the 10% RAM hit, like, RAM is constantly being refreshed,
and when the "point of refresh" intersects the program counter, execution
(instruction fetch) is stalled briefly while the code is refreshed?
Do other/all computers behave this way? Did the "classic" Apple II's avoid
it by doing refresh in a different part of the cycle than memory reads?
How 'bout the IIc Plus? Back to the IIgs, is refresh the same on the
motherboard as in the memory expansion slot? How 'bout DOC RAM?
--
-- Jay    jay.krell@cornell.edu    http://crux4.cit.cornell.edu/~jmk3 --