7600 memory

[Kim Schumann]

In 1977 what was the largest amount of central memory could you get in a CDC
Cyber 7600?

I am trying to compare memory densities from that period to those of the the
current era.

Thank you in advance,

Kim

[GaryBrandt]

The answer to the question is a little complex. The 7600 had up to 64K
words of main memory (small core memory SCM) from which it could
execute instructions and store data and up to 512K words of secondary
memory (large core memory LCM) from which the CPU could directly access
data at a reduced rate but was primarily used to 'page' blocks of data
to and from SCM.

Each word of memory was 60 bits. A word could hold 1, 2, or 4
instuctions, one floating point number or multiple integers. There were
no 'bytes' in that concept...all though the CDC machines used a 6 bit
character code to store a 'text' character. So, in that context, a word
could store 10 characters for a total of 640K chars of SCM and 5120K
chars of LCM.

That would be the closest comparison to a machine in bytes, but perhaps
the best way to express the memory capacity would be to compare the
sizes in bits!

In the mid 70's CDC began replacing the core memory with IC memory
which resulted in an increase in size. This was done producing several
models using the 7600 CPU and various configurations and speeds of
memory. Interestingly, the earlier 6600 actually could have more memory
(if I remember correctly up to 131K words)...the 7600 memory was
limited more by the physical design of the machine and the memory cost.


Wikipedia has excellent descriptions of many of the CDC models.

[Mark Riordan`]

In article <C0FE66A3.33E74%***@instrumental.com>, ***@instrumental.com
says...

Post by Kim Schumann
In 1977 what was the largest amount of central memory could you get in a CDC
Cyber 7600?
I am trying to compare memory densities from that period to those of the the
current era.

I was interested in Gary Brandt's reply, stating that the 7600
was limited to 64K words. I had believed that it could go up
to 128K words (aka 131K words), like its older brother.

Nevertheless, using a 7600 as a machine representative of
CDC's offerings in 1977 is misleading. The 7600, though still
a fast machine by the standards of 1977, was 8 years old
at that time. I suspect (but have been unable to confirm) that
CDC stopped making 7600s well before 1977. There were follow-on
machines that were compatible with the 7600. I believe they
had maximum SCM capacities of 256K words (aka 262K words).

Mark R

[Kim Schumann]

Mark and Gary,

Thanks for the feedback.

Based upon Mark's comments, would the 205 be better system to use for the
comparison?

Post by Mark Riordan`
says...

Post by Kim Schumann
In 1977 what was the largest amount of central memory could you get in a CDC
Cyber 7600?
I am trying to compare memory densities from that period to those of the the
current era.

I was interested in Gary Brandt's reply, stating that the 7600
was limited to 64K words. I had believed that it could go up
to 128K words (aka 131K words), like its older brother.
Nevertheless, using a 7600 as a machine representative of
CDC's offerings in 1977 is misleading. The 7600, though still
a fast machine by the standards of 1977, was 8 years old
at that time. I suspect (but have been unable to confirm) that
CDC stopped making 7600s well before 1977. There were follow-on
machines that were compatible with the 7600. I believe they
had maximum SCM capacities of 256K words (aka 262K words).
Mark R

[Eugene Miya]

Post by Kim Schumann
Based upon Mark's comments, would the 205 be better system to use for the
comparison?

Well, it's about 10 years and 3 machines 7600-> Star 100-> 203-> 205 later.
Not counting 8600.
And it had virtual memory.

--

[Scott Dorsey]

Post by Kim Schumann
Based upon Mark's comments, would the 205 be better system to use for the
comparison?

The 205 is several generations newer, and it really wasn't a very common
system. It also had virtual memory so you didn't have to worry about
overlays or unicorns.
--scott

[GaryBrandt]

Which machine you should use depends upon the question you are trying
to answer...the 7600 was first shipped in 1969 so it represents
technology of the time. By 1977 most of the world had switched from
magnetic core memory to ic memory, and the 7600 was no longer
manufactured in its original form.

By capacity, the 6600 actually had a bigger maximum memory capacity
when introduced in 1964. (131K CM, 2M ECS) In the 7600, it was limited
to what I stated (I verified this morning) by the physical design of
the machine (not the addressing capability, but the physical chassis)
to 64K SCM/ 512K LCM. So, if you are trying to answer the question of
largest memory capacity, the 7600 is not a good choice at any date. It
was however the DENSEST core memory, ie the 7600 had less memory than
the 6600, but it was physically much denser and quicker. (275 nsec
cycle time versus 1000 nsec).

We used the 7600 CPU and married it to CMOS memory and 10K ECL ppus in
the Cyber 175 around 1974 which increased the maximum size to 262K CM;
along with the 6000 ECS max of 2M. (We were also able to decrease the
CPU clock period to Seymour's original goal of 25 ns) The Cyber 176 had
the same CPU with bipolar memory a little later. The 7600 CPU lived on
into a couple of early Cyber 180 versions, some of which are still
active at the Pave Paws sites.

There are two resources that I suggest. www.cray-cyber.org has a good
timeline of the cdc machines thanks to the preservation work of our
friends in Germany. And you can find hardware reference manuals for
many of the machines on www.bitsavers.org due to the work of people
dedicated to preserving and making available such information. I think
that Al just bought a Cyber 205 manual on ebay a couple of days ago, so
he should have that available sometime. And again, check wikipedia
writeups, they are excellent.

[Eugene Miya]

Post by GaryBrandt
There are two resources that I suggest. www.cray-cyber.org has a good

.....

Post by GaryBrandt
I think that Al just bought a Cyber 205 manual on ebay a couple of days ago,
he should have that available sometime. And again, check wikipedia
writeups, they are excellent.

I feel bad that Al had to buy that manual. Alas, I tossed all my 205
docs for the brief time I had them about our 4-pipe machine. Hugh is no
longer interested in the topic.

You need to be REALLY circumspect about Wikipedia especially on anything
having to do with high performance machines (which not many of the
public have access to). I used "Grand Challenge" as a test case.
It pointed ONLY to the DARPA car race. That is VERY bad.
So I filled out the redirection page (a minimal cut and paste thing to do),
and I am pondering what links to add.

--