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Posted By

SVS
on 2013-09-26
14:35:02
 How much ROM is faster than RAM

ROM access is surely faster than RAM. Then I was thinking if anybody did try to measure what is the ratio.
I mean a routine running from ROM compared with the same code running from RAM.
What do you think about?

Posted By

Csabo
on 2013-09-26
14:39:54
 Re: How much ROM is faster than RAM

They should be exactly the same, I think. Regardless of where you're calling, doing an LDA#$00 (for example) will take exactly two cycles.

Posted By

MMS
on 2013-09-28
17:30:48
 Re: How much ROM is faster than RAM

Hm, as per my memories the ROMs typically slower than RAM, maybe valid from intel8088 system onwards only. If you copy the ROM into RAM, no need to switch between them and you save some time happy

Posted By

Degauss
on 2013-09-28
18:28:18
 Re: How much ROM is faster than RAM

It will be exactly the same speed. We only got one clock in our computers, right?

Posted By

siz
on 2013-09-29
03:49:36
 Re: How much ROM is faster than RAM

RAM's are faster than ROMs for a long time. From the early 90s (or late 80s) when CPU clocks (1 cycle) were faster than the typical access time of memories it became a factor to quicken memory access so they started using the so called shadow ROM (copying contents of ROM to the underlying RAM area and).
In case of the plus/4 RAM and ROM access are both quicker than the CPU cycle so their access times are indifferent, you won't sense any difference (as the former posters said before)

Posted By

Litwr
on 2013-09-30
14:05:01
 Re: How much ROM is faster than RAM

ROM is faster to read at Basic because the read access to RAM uses CHRGOT.

Posted By

zorkon
on 2013-10-04
13:31:21
 Re: How much ROM is faster than RAM

Interesting how such a simple question can generate so much misinformation.

- The Plus/4 clock frequency is so slow that neither RAM nor ROM access speed are limiting speed in any way. The access speed is exactly the same for both.
- On 90ies PCs there was a time when RAM access was 16 or 32bit, while the BIOS was stored in an 8 bit EPROM. Therefore ROM access speed could be increased by copying the BIOS to RAM. Nowadays the BIOS is only needed to boot the pc, so who cares...

Posted By

sanap kalinda
on 2016-06-27
06:38:30
 Re: How much ROM is faster than RAM

RAM is typically faster than ROM...

Posted By

Csabo
on 2016-06-27
10:26:48
 Re: How much ROM is faster than RAM

I wouldn't say misinformation, just confusion, because the original question, and several of the terms used are ambiguous. Otherwise several (seemingly contradictory) things said above are correct. Let's break it down:

Time it takes for the processor to read one byte (basically an LDA statement): it's the same. For example, an LDA$8000 could read either from ROM or RAM, but it will be always exactly 4 cycles. (This was correctly pointed out by Degauss and zorkon above.)

Time it takes to read byte from BASIC (which is what I suspect SVS is originally asking): this could very well be different, I'm going to trust what Litwr said above. However, it doesn't have to do with the speed of RAM or ROM chips, but rather how the BASIC statement is translated to machine code. If there's more paging involved for one of them, it will be different.

And finally, the actual speed of the RAM and ROM chips: probably different, but this doesn't matter. I know nothing of hardware stuff, but several folks pointed this out, so I'm going to assume they are right.

Now, did that clear everything up? happy



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