Re: faster CPU and the Lisa OS

In most configurations, the X/ProFile is substantially faster than an Apple ProFile. How much depends on the media you use and what parameters you are measuring.

A parallel port hard disk access involves a number of stages:

1) Initial handshake/response
2) Command transfer/acknowledge
3) Data transfer
4) (Writes only) Completion acknowledge

The data transfer rate is fixed by the Lisa CPU, so a faster CPU would improve the transfer rate and the hard disk cannot affect this. This puts a limit on the amount of improvement that can be obtained with a faster hard disk system.

The media's read access time affects the delay before the data transfer, and the write time affects the delay before the completion acknowledge. Compact Flash has very little latency, so it behaves faster in single sector random tests, but a modern IDE drive (with a full track cache or read-ahead algorithm) can measure faster than CF using a performance measurement application such as SCSI Evaluator.

The X/ProFile hardware/software directly affects the handshake and acknowledge stages, so some effort was made to minimize its response time. The Lisa needs to wait quite a while for the original ProFile to respond at these stages. In many cases the X/ProFile responds by the time the Lisa first checks to see if it has, yielding the highest performance possible.

>Are you sure that the "lag" you experience is CPU/RAM related? I
>don't "feel" any difference with 2 Meg RAM over the standard 1 Meg.
> LOS seems to do a lot of disk IO, and a CPU upgrade won't do much
>to make an old Profile any faster. A better LOS upgrade may be to
>get an X/Profile. I know that "speed" was not the main design
>objective for the X/Profile, but James could verify if it is really
>any faster.

-- 
-- 
-----
You received this message because you are a member of the LisaList group.
The group FAQ is at http://lowendmac.com/lists/lisa.html
To post to this group, send email to lisalist_at_email.domain.hidden
To leave this group, send email to lisalist+unsubscribe_at_email.domain.hidden
For more options, visit this group at http://groups.google.com/group/lisalist
--- 
You received this message because you are subscribed to the Google Groups "LisaList" group.
To unsubscribe from this group and stop receiving emails from it, send an email to lisalist+unsubscribe_at_googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.